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  • 51.
    Ahlberg, Joakim
    Swedish National Road and Transport Research Institute, Society, environment and transport, Transport economics Stockholm.
    Revenues in discrete multi-unit, common value auctions: a study of three sealed-bid mechanisms2009In: Portuguese economic journal, ISSN 1617-9838, Vol. 8, no 1, p. 21p. 3-14Article in journal (Refereed)
    Abstract [en]

    We propose in this paper a discrete bidding model, both on quantities and in pricing. It has a two-unit demand environment where subjects bid for contracts with an unknown redemption value, common to all bidders. Prior to bidding, the bidders receive private signals of information on the (common) value. Both the value and the signals are drawn from a known discrete affiliated joint distribution. The relevant task for the paper is to compare equilibrium strategies and the seller's revenue between the three auction formats. We find that, among the three auction formats below with two players, the Vickrey auction always gives the most revenue to the seller, where the discriminatory auction becomes second and the uniform auction last. We also find that, in equilibrium, bidders bid the same amount on both items in the discriminatory auction; a phenomenon we do not notice in either of the other two auction formats. There, different amount of demand reduction is encountered.

  • 52.
    Ahlberg, Joakim
    et al.
    Ramböll .
    Ericson, Johan
    WSP.
    Johansson, Oskar
    Swedish National Road and Transport Research Institute, Society, environment and transport, Transport economics.
    Ridderstedt, Ivan
    Swedish National Road and Transport Research Institute, Society, environment and transport, Transport economics.
    Marginalkostnad för luftfartens infrastruktur2017Report (Other academic)
    Abstract [en]

    The main purpose of this study is to estimate the marginal costs of aviation infrastructure. But since it not exist a uniform definition of what is the cost base of the aviation infrastructure, there is also a discussion of what costs should be included. An additional purpose of the study is to relate the estimated marginal costs to today's pricing and to investigate whether aviation pays its socio-economic costs.

    Estimates of the marginal cost of utilizing (relevant) airport infrastructure and for operating airline infrastructure is being analyzed using cost data from Stockholm Arlanda Airport and the Civil Aviation Authority. The empirical approach used to analyze cost items is a regression analysis, with adjustments for month-specific variations in travel patterns, when the airport section is investigated, and taking into account regional differences for airports when investigating air traffic control in the towers.

    There are some uncertainties in the study, but in the light of this, the results indicate that the average marginal cost of the infrastructure is around SEK 13 per passenger and SEK1,168 per aircraft started. Corresponding estimation for air traffic management is also uncertain, with results indicating a marginal cost of SEK 373 per flight. Furthermore, it appears that the revenue from marginal cost-based charges could not alone finance the state aviation infrastructure.

  • 53.
    Ahlberg, Joakim
    et al.
    Swedish National Road and Transport Research Institute, Society, environment and transport, Transport economics Stockholm.
    Johansson, Anna
    Swedish National Road and Transport Research Institute, Society, environment and transport, Transport economics Stockholm.
    Etablering av konkurrerande snabbtågstrafik på Västra stambanan: översyn ur marknadens synvinkel2014Report (Other academic)
    Abstract [en]

    As of October 2010 the railway market is liberalised. As a result, other operators than SJ could apply for track capacity also for long-distance passenger services, and the timetable for 2012 was the first timetable that was affected by the liberalisation. The Swedish railway network has, by definition, capacity restrains. The Swedish Transport Administration (Trafikverket) allocates capacity among those railway traffic operators that has applied for track capacity in the annual capacity allocation process. In the capacity allocation process for the 2014 timetable, four operators applied for capacity for long-distance high-speed train traffic between Gothenburg and Stockholm. In several cases the operators applied for the same train paths, which put Trafikverket’s applying of the process, the use of coordination and prioritization criteria, to the test for the first time since the liberalisation. VTI has interviewed the three largest of the above operators to receive information about how they experienced the capacity allocation process leading to the timetable for 2014 and to get their views on the possible obstacles that may exist for establishing a new operator on the railway market. The study was commissioned by the Swedish Transport Agency as a basis for their market surveillance in the area. The operators that are challenging SJ perceive that the capacity allocation process does not meet the requirement for competitive neutrality and non-discrimination. Both operators see the need for a more transparent process, with priority criteria that provide a more predictable outcome and which is carried out by the help of computerized tools so that the process can be implemented more efficiently and provide a more effective outcome. They argue that the construction of a timetable is so complex that it is difficult to, as now being done, manually make the most effective adjustments in the timetable necessary due to competing applications. The challenging operators therefore call for a review of the process to assess in which areas it can be improved.

  • 54.
    Ahlberg, Joakim
    et al.
    Swedish National Road and Transport Research Institute, Society, environment and transport, Transport economics, TEK.
    Nilsson, Jan-Eric
    Swedish National Road and Transport Research Institute, Society, environment and transport, Transport economics, TEK.
    Ad hoc-processen: hur används ledig kapacitet i järnvägsnätet?2016Report (Other academic)
    Abstract [en]

    After the Swedish Transport Administration’s adoption of next year's timetable in mid-fall each year, starts the so-called ad hoc process, i.e. requests for train paths that can use spare capacity in the network. VTI received in September 2015 Transport Agency's mission to deepen the understanding of the ad hoc-process, This “notat” reports that assignment. In light of the description that was made, the intention was to also find the measure of the importance of this process in relation to the process leading to adopting a final schedule. It has been found that the Transport Administration’s various information management systems are not designed to enable such a description.

    Thanks to a recent statistical tool, it is possible to observe that nearly 97 percent of the passenger trains booked into the annual timetable process, also actually run. This refers to two thirds of the timetable year 2015. The aim of the Transport Agency/Traffic analysis is to, in the near future, also report similar information about freight train. Behind this figure conceals both an outflow and an inflow of traffic that will be conducted in accordance with the timetable set out in the autumn of each year. However, there is no knowledge of when these changes are implemented, which is of great importance for assessing the degree of flexibility in the ad hoc process. This situation may change as a result of the Transport Agency as of the timetable relating to 2016 for the charges to cancel the allocated capacity. The fee will be higher the closer to the scheduled departure of the train the application is withdrawn. This can help improve the flexibility in the use of the track capacity not reserved in the annual timetabling process. Another consequence may be that the information on the process will improve.

  • 55.
    Ahlin, S
    et al.
    Swedish National Road and Transport Research Institute.
    Thoren, H
    Swedish National Road and Transport Research Institute.
    Bergtekniska egenskaper hos gnejser. ( Byggnadsindustrin 1978, nr 39)1979Report (Other academic)
  • 56.
    Ahlstrand, Ingemar
    Swedish National Road and Transport Research Institute.
    Beslutsprocessen för infrastrukturella investeringar från Scanlink till KomKom1997Report (Other (popular science, discussion, etc.))
  • 57.
    Ahlström, Christer
    et al.
    Swedish National Road and Transport Research Institute, Traffic and road users, Human-vehicle-transport system interaction.
    Andersson, Jan
    Swedish National Road and Transport Research Institute, Traffic and road users, Human-vehicle-transport system interaction.
    Anund, Anna
    Swedish National Road and Transport Research Institute, Traffic and road users, Human-vehicle-transport system interaction.
    Börjesson, Emma
    Scania.
    Johansson, Hanna
    Scania.
    Johnsson, Johanna
    Scania.
    Detecting sleepiness by Optalert: final report2010Report (Other academic)
    Abstract [en]

    Many crashes with heavy vehicle can be attributed to driver sleepiness or driving impairment due to sleepiness, and it is important to find methods to predict those situations and counteract this problem. The Optalert fatigue management system claims to be able to detect sleepiness. The aims of this study are to (a) evaluate if Optalert can detect sleepiness equally well as other sleepiness indicators and (b) if the data patterns obtained by Optalert correlates with these other sleepiness indicators. Twelve sleep deprived truck drivers drove for about 90 minutes in an advanced moving base truck simulator. The experimental setup, including the sleep deprivation, was designed so that the drivers should become increasingly sleepier during the trial and the intention was that they should fall asleep during the experiment.

    Four different indicators of sleepiness or driving impairment due to sleepiness were used to monitor the state of the drivers; the Karolinska Sleepiness Scale (KSS), the variability in lateral position (SDLP), the blink duration and the Optalert system. The results show that all four sleepiness indicators increased with time on task. An analysis of variance revealed that the changes were significant for KSS, blink duration and the Optalert system, and a correlation analysis showed that Optalert correlated significantly with blink duration and SDLP. However, even though these correlations were significant, they were all rather low with a maximum correlation coefficient of 0.24.

    In conclusion, the Optalert system is promising and the sleepiness rating provided by the system works at least equally well as the other three sleepiness indicators. There are some practical limitations to the system; there is no reliable threshold which can be used to determine when a driver is getting too sleepy to drive (this is also the case for other available sleepiness indicators), the driver needs to be attached to the vehicle via the spectacle frames and a wire, and the quality of the eye movement recordings often deteriorated when the driver started driving the truck. Moreover, during the experiment the technical reliability was sometimes low.

  • 58.
    Ahlström, Christer
    et al.
    Swedish National Road and Transport Research Institute, Traffic and road users, Human Factors in the Transport System.
    Anund, Anna
    Swedish National Road and Transport Research Institute, Traffic and road users, Human Factors in the Transport System.
    Fors, Carina
    Swedish National Road and Transport Research Institute, Traffic and road users, Human Factors in the Transport System.
    Åkerstedt, Torbjörn
    Karolinska Institutet.
    Effects of the road environment on the development of driver sleepiness in young male drivers2018In: Accident Analysis and Prevention, ISSN 0001-4575, E-ISSN 1879-2057, Vol. 112, p. 127-134Article in journal (Refereed)
    Abstract [en]

    Latent driver sleepiness may in some cases be masked by for example social interaction, stress and physical activity. This short-term modulation of sleepiness may also result from environmental factors, such as when driving in stimulating environments. The aim of this study is to compare two road environments and investigate how they affect driver sleepiness. Thirty young male drivers participated in a driving simulator experiment where they drove two scenarios: a rural environment with winding roads and low traffic density, and a suburban road with higher traffic density and a more built-up roadside environment. The driving task was essentially the same in both scenarios, i.e. to stay on the road, without much interaction with other road users. A 2 x 2 design, with the conditions rural versus suburban, and daytime (full sleep) versus night-time (sleep deprived), was used. The results show that there were only minor effects of the road environment on subjective and physiological indicators of sleepiness. In contrast, there was an increase in subjective sleepiness, longer blink durations and increased EEG alpha content, both due to time on task and to night-time driving. The two road environments differed both in terms of the demand on driver action and of visual load, and the results indicate that action demand is the more important of the two factors. The notion that driver fatigue should be countered in a more stimulating visual environment such as in the city is thus more likely due to increased task demand rather than to a richer visual scenery. This should be investigated in further studies.

  • 59.
    Ahlström, Christer
    et al.
    Swedish National Road and Transport Research Institute, Traffic and road users, Human Factors in the Transport System.
    Anund, Anna
    Swedish National Road and Transport Research Institute, Traffic and road users, Human Factors in the Transport System.
    Fors, Carina
    Swedish National Road and Transport Research Institute, Traffic and road users, Human Factors in the Transport System.
    Åkerstedt, Torbjörn
    Stockholms Universitet.
    The effect of daylight versus darkness on driver sleepiness: A driving simulator study2017In: Journal of Sleep Research, ISSN 0962-1105, E-ISSN 1365-2869Article in journal (Refereed)
    Abstract [en]

    Driver sleepiness studies are often carried out with alert drivers during daytime and sleep-deprived drivers during night-time. This design results in a mixture of different factors (e.g. circadian effects, homeostatic effects, light conditions) that may confound the results. The aim of this study was to investigate the effect of light conditions on driver sleepiness. Thirty young male drivers (23.6 ± 1.7 years old) participated in a driving simulator experiment where they drove on a rural road. A 2 × 2 design was used with the conditions daylight versus darkness, and daytime (full sleep) versus night-time (sleep deprived). The results show that light condition had an independent effect on the sleepiness variables. The subjective sleepiness measured by Karolinska Sleepiness Scale was higher, lateral position more left-oriented, speed lower, electroencephalogram alpha and theta higher, and blink durations were longer during darkness. The number of line crossings did not change significantly with light condition. The day/night condition had profound effects on most sleepiness indicators while controlling for light condition. The number of line crossings was higher during night driving, Karolinska Sleepiness Scale was higher, blink durations were longer and speed was lower. There were no significant interactions, indicating that light conditions have an additive effect on sleepiness. In conclusion, Karolinska Sleepiness Scale and blink durations increase primarily with sleep deprivation, but also as an effect of darkness. Line crossings are mainly driven by the need for sleep and the reduced alertness at the circadian nadir. Lane position is, however, more determined by light conditions than by sleepiness.

  • 60.
    Ahlström, Christer
    et al.
    Swedish National Road and Transport Research Institute, Traffic and road users, Human-vehicle-transport system interaction.
    Bolling, Anne
    Swedish National Road and Transport Research Institute, Traffic and road users, Vehicle technology and simulation.
    Sörensen, Gunilla
    Swedish National Road and Transport Research Institute, Traffic and road users, Traffic safety, society and road-user.
    Eriksson, Olle
    Swedish National Road and Transport Research Institute, Infrastructure, Infrastructure maintenance.
    Andersson, Anders
    Swedish National Road and Transport Research Institute, Traffic and road users, Vehicle technology and simulation.
    Validating speed and road surface realism in VTI driving simulator III2012Report (Other academic)
    Abstract [en]

    New simulator models concerning vibration, noise and graphics have been designed and implemented in the VTI Simulator III. The objective of this study is to validate this simulator in terms of road surface realism. Twenty-four drivers participated in the study and drove the same route both in the simulator and on real roads. Three road sections ranging from very smooth to rather uneven were incorporated in the design. The comparison included the objective driving parameter speed as well as subjective parameters from questionnaires and rating scales (evenness, quietness and comfort level). A road section with five speed limit changes was of particular interest in the analyses. No statistically significant difference could be found between the simulator and the car, neither in the parameter speed (in sections with no speed limit changes) nor in the ratings evenness and quietness. Despite similar speed profiles surrounding the speed limit signs, there was a statistically significant difference between the speed in the car and in the simulator, with more rapid accelerations and decelerations in the simulator. The comfort rating was shown to be higher in the car compared to the simulator, but in both cases the general trend showed higher comfort on smoother roads. These results indicate absolute validity for the ratings evenness and quietness, and for the measure speed, and relative validity for comfort and speed surrounding speed limit signs.

  • 61.
    Ahlström, Christer
    et al.
    Swedish National Road and Transport Research Institute, Traffic and road users, Human-vehicle-transport system interaction.
    Dukic, Tania
    Swedish National Road and Transport Research Institute, Traffic and road users, Human-vehicle-transport system interaction.
    Comparison of eye tracking systems with one and three cameras2011In: ACM International Conference Proceeding Series, 2011Conference paper (Refereed)
    Abstract [en]

    When using eye movements to determine the state of a car driver it is important that the eye tracker is robust, unobtrusive, inexpensive and fully automatic. The objectives of this study are to compare the performance of a one-camera system with a three-camera system and to investigate if the accuracy and availability of the one-camera system is sufficient to monitor driver state. Data from 53 subjects were evaluated and the results indicate that there is not much difference between a single-camera system and a multi-camera system as long as the driver is looking straight ahead. However, with more peripheral gaze directions, the larger coverage that is provided by the additional cameras works in favour of the multi-camera system. © ACM 2010.

  • 62.
    Ahlström, Christer
    et al.
    Swedish National Road and Transport Research Institute, Traffic and road users, Human-vehicle-transport system interaction.
    Dukic, Tania
    Swedish National Road and Transport Research Institute, Traffic and road users, Human-vehicle-transport system interaction.
    Ivarsson, Erik
    SmartEye.
    Kircher, Albert
    Swedish National Road and Transport Research Institute.
    Rydbeck, Bosse
    SmartEye.
    Viström, Matias
    Saab Automobile.
    Performance of a one-camera and a three-camera system2010Report (Other academic)
    Abstract [en]

    Driving and operating a vehicle is to a great extent a visual task. In driver behaviour studies it is therefore important to be able to measure where the driver is looking. Today this can be done unobtrusively and remotely in real-time with camera based eye tracking. The most common remote eye tracking systems use multiple cameras in order to give satisfactory results. However, promising results using only one camera has recently emerged on the market. The main objective of this study is to compare eye tracking systems with one and three cameras, respectively, during various measurement conditions.

    A total of 53 participants were enrolled in the study. Data from the two eye trackers were acquired and analysed in terms of availability, accuracy and precision. The results indicate that both availability and accuracy are affected by many different factors. The most important factors are the number of cameras that is used and the angular distance from straight ahead. In the central region (straight ahead) both one-camera and three-camera systems have a high degree of accuracy and availability, but with increasing distance from the central region, the results deteriorate. This effect falls harder upon the one-camera system. Interestingly, there were no significant effects when wearing glasses in either availability or accuracy. There was however an interaction effect between distance and glasses.

    Advantages with a one-camera system are that it is cheaper, easier to operate and easier to install in a vehicle. A multi-camera system will, on the other hand, provide higher availability and accuracy for areas that are far from the road centre. A one-camera system is thus mostly suitable for in-vehicle applications such as systems that warn drivers for sleepiness or distraction while multi-camera solutions are preferable for research purposes.

  • 63.
    Ahlström, Christer
    et al.
    Swedish National Road and Transport Research Institute, Traffic and road users, Human-vehicle-transport system interaction.
    Fors, Carina
    Swedish National Road and Transport Research Institute, Traffic and road users, Human-vehicle-transport system interaction.
    Anund, Anna
    Swedish National Road and Transport Research Institute, Traffic and road users, Human-vehicle-transport system interaction.
    Hallvig, David
    Stockholms Universitet.
    Video-based observer rated sleepiness versus self-reported subjective sleepiness in real road driving2015In: European Transport Research Review, ISSN 1867-0717, E-ISSN 1866-8887, Vol. 7, no 4, article id 38Article in journal (Refereed)
    Abstract [en]

    Observer-rated sleepiness (ORS) based on video recordings of the driver’s face is often used when analysing naturalistic driving data. The aim of this study is to investigate if ORS ratings agree with subjective self-reported sleepiness (SRS).

    Forty raters assessed 54 video-clips showing drivers with varying levels of sleepiness. The video-clips were recorded during a field experiment focusing on driver sleepiness using the same cameras that are typically used in large-scale field studies. The weak results prompted a second test. Ten human factors researchers made pairwise comparisons of videos showing the same four participants in an alert versus a very sleepy condition. The task was simply to select the video-clip where the driver was sleepy.

    The overall average percentage of video segments where ORS and SRS matched was 41 % in Test 1. ORS 0 (alert) and ORS 2 (very sleepy) were easier to score than ORS 1 and it was slightly harder to rate night-time drives. Inter-rater agreement was low, with average Pearson’s r correlations of 0.19 and Krippendorff’s alpha of 0.15. In Test 2, the average Pearson’s r correlations was 0.35 and Krippendorff’s alpha was 0.62. The correspondence between ORS and SRS showed an agreement of 35 %.

    The results indicate that ORS ratings based on real road video recordings correspond poorly with SRS and have low inter-rater agreement. Further research is necessary in order to further evaluate the usefulness of ORS as a measure of sleepiness.

  • 64.
    Ahlström, Christer
    et al.
    Swedish National Road and Transport Research Institute, Traffic and road users, Human-vehicle-transport system interaction.
    Fors, Carina
    Swedish National Road and Transport Research Institute, Traffic and road users, Human-vehicle-transport system interaction.
    Forward, Sonja
    Swedish National Road and Transport Research Institute, Society, environment and transport, Mobility, actors and planning processes.
    Gregersen, Nils Petter
    Swedish National Road and Transport Research Institute, Society, environment and transport, Mobility, actors and planning processes.
    Hjälmdahl, Magnus
    Swedish National Road and Transport Research Institute, Traffic and road users, Human-vehicle-transport system interaction.
    Jansson, Jonas
    Swedish National Road and Transport Research Institute, Traffic and road users.
    Kircher, Katja
    Swedish National Road and Transport Research Institute, Traffic and road users, Human-vehicle-transport system interaction.
    Lindberg, Gunnar
    Swedish National Road and Transport Research Institute, Society, environment and transport, Transport economics Stockholm.
    Nilsson, Lena
    Swedish National Road and Transport Research Institute, Traffic and road users.
    Patten, Christopher
    Swedish National Road and Transport Research Institute, Traffic and road users, Human-vehicle-transport system interaction.
    Dangerous use of mobile phones and other communication devices while driving: A toolbox of counter-measures2013In: Proceedings of the 16th International Conference Road Safety on Four Continents: Beijing, China. 15-17 May 2013, Linköping: Statens väg- och transportforskningsinstitut, 2013Conference paper (Other academic)
    Abstract [en]

    The use of mobile phone and similar devices while driving has been a topic of discussion and research for several years. It is now an established fact that driving performance is deteriorated due to distraction but no clear conclusions can yet be drawn concerning influence on crash rates. Better studies on this relationship is needed. Most countries in Europe and many countries elsewhere have introduced different types of bans for handheld devices. Sweden has, however, no such bans. VTI was commissioned by the Swedish Government to outline possible means to reduce the dangerous usage of mobile phones and other communication devices while driving as alternatives to banning. This task was a result of a previous VTI-state-of-the-art review of research on mobile phone and other communication device usage while driving. One of the findings in the review was that bans on handheld phones did not appear to reduce the number of crashes.

    Eighteen different countermeasures in three main areas were suggested. (1) Technical solutions such as countermeasures directed towards the infrastructure, the vehicle and the communication device. (2) Education and information, describing different ways to increase knowledge and understanding among stakeholders and different driver categories. (3) Different possibilities for how society, industry and organisations can influence the behaviour of individuals, via policies, rules, recommendations and incentives. Our conclusion is that a combination of different countermeasures is needed – where education and information to the drivers are combined with support and incentives for a safe usage of different communication devices.

  • 65.
    Ahlström, Christer
    et al.
    Swedish National Road and Transport Research Institute, Traffic and road users, Human Factors in the Transport System.
    Gink Lövgren, Maria
    Volvo Bus Corporation.
    Nilsson, Mats
    Volvo Bus Corporation.
    Dukic Willstrand, Tania
    Swedish National Road and Transport Research Institute, Traffic and road users, Human Factors in the Transport System.
    Anund, Anna
    Swedish National Road and Transport Research Institute, Traffic and road users, Human Factors in the Transport System.
    The effect of an active steering system on city bus drivers’ muscle activity2018In: International Journal of Occupational Safety and Ergonomics, ISSN 1080-3548, E-ISSN 2376-9130, p. 1-9Article in journal (Refereed)
    Abstract [en]

    City bus drivers spend hours driving under time pressure, in congested traffic and in a monotonous sitting position. This leads to unhealthy working conditions, especially in terms of physical and psychological stress. The aim of this study is to investigate whether an active steering system can alleviate the musculoskeletal stress involved in manoeuvring a bus. Twenty bus drivers drove a city bus equipped with the Volvo dynamic steering (VDS) support system in real traffic. Steering effort was evaluated with electromyography and with a questionnaire. Compared to baseline, VDS significantly reduced the required muscle activity by on average 15–25% while turning, and up to 68% in the part of the manoeuvre requiring maximum effort. The bus drivers believed that VDS will help reduce neck and shoulder problems, and they expressed a desire to have VDS installed in their own bus.

  • 66.
    Ahlström, Christer
    et al.
    Swedish National Road and Transport Research Institute, Traffic and road users, Trafikanttillstånd, TIL.
    Ihlström, Jonas
    Swedish National Road and Transport Research Institute, Traffic and road users, Trafikanttillstånd, TIL.
    Kircher, Katja
    Swedish National Road and Transport Research Institute, Traffic and road users, Trafikanttillstånd, TIL.
    Förares användning av kommunikationsutrustning under färd: Del 1: Enkätstudie. Del 2: Användning enligt objektiv mätning2017Report (Other academic)
    Abstract [sv]

    Av resultaten från denna enkät är något av det mest tydliga att saker som funnits i en bil en längre tid, exempelvis att ställa in radio, använda navigationsutrustning och prata i telefon, görs i betydligt högre utsträckning än nyare saker som att skicka meddelanden, surfa på internet eller spela spel. Överlag tycks det vara låg acceptans för de nyare företeelserna och en stor andel av urvalet tycker att det är felaktigt eller olämpligt att hålla på med dessa aktiviteter. Att prata i telefon med handsfree tycks uppfattas av många som säkrare och mer lämpligt än att inte använda det. Detta avspeglas även i inställning till införandet av förbud, där en relativt stor andel accepterar att det ska vara lagligt att använda handsfreefunktioner men att annan användning av kommunikationsutrustning borde förbjudas.

    I den andra delen genomfördes en mätning av mobilanvändning under färd genom installerande tav en mobilapp. Den genomförda undersökningen är den första av sitt slag åtminstone i Sverige, så att den, trots vissa brister och begränsningar, kan leverera information som hittills har varit okänt. I detta del diskuteras resultaten, även i förhållande till enkätsvaren, följt av en reflektion över metoden och möjliga förbättringar, som är önskvärda inför en fortsättningsstudie.

  • 67.
    Ahlström, Christer
    et al.
    Swedish National Road and Transport Research Institute, Traffic and road users, Trafikanttillstånd, TIL.
    Jansson, Sabina
    Linköpings Universitet.
    Anund, Anna
    Swedish National Road and Transport Research Institute, Traffic and road users, Trafikanttillstånd, TIL.
    Local changes in the wake electroencephalogram precedes lane departures2017In: Journal of Sleep Research, ISSN 0962-1105, E-ISSN 1365-2869Article in journal (Refereed)
    Abstract [en]

    The objective of this exploratory study is to investigate if lane departures are associated with local sleep, measured via source-localized electroencephalography (EEG) theta power in the 5-9 Hz frequency range. Thirty participants drove in an advanced driving simulator, resulting in 135 lane departures at high levels of self-reported sleepiness. These lane departures were compared to matching non-departures at the same sleepiness level within the same individual. There was no correspondence between lane departures and global theta activity. However, at the local level an increased risk for lane departures was associated with increased theta content in brain regions related to motor function.

  • 68.
    Ahlström, Christer
    et al.
    Swedish National Road and Transport Research Institute, Traffic and road users, Human Factors in the Transport System.
    Kircher, Katja
    Swedish National Road and Transport Research Institute, Traffic and road users, Human Factors in the Transport System. Linköpings Universitet.
    A Generalized Method to Extract Visual Time-Sharing Sequences From Naturalistic Driving Data2017In: IEEE transactions on intelligent transportation systems (Print), ISSN 1524-9050, E-ISSN 1558-0016, Vol. 18, no 11, p. 2929-2938Article in journal (Refereed)
    Abstract [en]

    Indicators based on visual time-sharing have been used to investigate drivers' visual behaviour during additional task execution. However, visual time-sharing analyses have been restricted to additional tasks with well-defined temporal start and end points and a dedicated visual target area. We introduce a method to automatically extract visual time-sharing sequences directly from eye tracking data. This facilitates investigations of systems, providing continuous information without well-defined start and end points. Furthermore, it becomes possible to investigate time-sharing behavior with other types of glance targets such as the mirrors. Time-sharing sequences are here extracted based on between-glance durations. If glances to a particular target are separated by less than a time-based threshold value, we assume that they belong to the same information intake event. Our results indicate that a 4-s threshold is appropriate. Examples derived from 12 drivers (about 100 hours of eye tracking data), collected in an on-road investigation of an in-vehicle information system, are provided to illustrate sequence-based analyses. This includes the possibility to investigate human-machine interface designs based on the number of glances in the extracted sequences, and to increase the legibility of transition matrices by deriving them from time-sharing sequences instead of single glances. More object-oriented glance behavior analyses, based on additional sensor and information fusion, are identified as the next future step. This would enable automated extraction of time-sharing sequences not only for targets fixed in the vehicle's coordinate system, but also for environmental and traffic targets that move independently of the driver's vehicle.

  • 69.
    Ahlström, Christer
    et al.
    Swedish National Road and Transport Research Institute, Traffic and road users, Trafikanttillstånd, TIL.
    Kircher, Katja
    Swedish National Road and Transport Research Institute, Traffic and road users, Trafikanttillstånd, TIL. Linköping University.
    Changes in glance behaviour when using a visual eco-driving system: A field study2017In: Applied Ergonomics, ISSN 0003-6870, E-ISSN 1872-9126, Vol. 58, p. 414-423Article in journal (Refereed)
    Abstract [en]

    While in-vehicle eco-driving support systems have the potential to reduce greenhouse gas emissions and save fuel, they may also distract drivers, especially if the system makes use of a visual interface. The objective of this study is to investigate the visual behaviour of drivers interacting with such a system, implemented on a five-inch screen mounted above the middle console. Ten drivers participated in a real-world, on-road driving study where they drove a route nine times (2 pre-baseline drives, 5 treatment drives, 2 post-baseline drives). The route was 96 km long and consisted of rural roads, urban roads and a dual-lane motorway.

    The results show that drivers look at the system for 5–8% of the time, depending on road type, with a glance duration of about 0.6 s, and with 0.05% long glances (>2s) per kilometre. These figures are comparable to what was found for glances to the speedometer in this study. Glance behaviour away from the windscreen is slightly increased in treatment as compared to pre- and post-baseline, mirror glances decreased in treatment and post-baseline compared to pre-baseline, and speedometer glances increased compared to pre-baseline. The eco-driving support system provided continuous information interspersed with additional advice pop-ups (announced by a beep) and feedback pop-ups (no auditory cue). About 20% of sound initiated advice pop-ups were disregarded, and the remaining cases were usually looked at within the first two seconds. About 40% of the feedback pop-ups were disregarded. The amount of glances to the system immediately before the onset of a pop-up was clearly higher for feedback than for advice.

  • 70.
    Ahlström, Christer
    et al.
    Swedish National Road and Transport Research Institute, Traffic and road users, Human-vehicle-transport system interaction.
    Kircher, Katja
    Swedish National Road and Transport Research Institute, Traffic and road users, Human-vehicle-transport system interaction.
    Review of real-time visual driver distraction detection algorithms2011In: ACM International Conference Proceeding Series, 2011Conference paper (Refereed)
    Abstract [en]

    Many incidents and crashes can be attributed to driver distraction, and it is essential to learn how to detectdistraction in order to develop efficient countermeasures. A number of distraction detection algorithms have been developed over the years, and the objective of this paper is to summarize available approaches and to describe these algorithms in a unified framework. The review is limited to real-time algorithms that are intended to detect visual distraction.

  • 71.
    Ahlström, Christer
    et al.
    Swedish National Road and Transport Research Institute, Traffic and road users, Human-vehicle-transport system interaction.
    Kircher, Katja
    Swedish National Road and Transport Research Institute, Traffic and road users, Human-vehicle-transport system interaction.
    Fors, Carina
    Swedish National Road and Transport Research Institute, Traffic and road users, Human-vehicle-transport system interaction.
    Dukic, Tania
    Swedish National Road and Transport Research Institute, Traffic and road users, Human-vehicle-transport system interaction.
    Patten, Christopher
    Swedish National Road and Transport Research Institute, Traffic and road users, Human-vehicle-transport system interaction.
    Anund, Anna
    Swedish National Road and Transport Research Institute, Traffic and road users, Human-vehicle-transport system interaction.
    Measuring driver impairments: Sleepiness, distraction, and workload2012In: IEEE Pulse, ISSN 2154-2287, Vol. 3, no 2, p. 22-30Article in journal (Refereed)
    Abstract [en]

    Snow was falling heavily when Sarah was driving on a slippery road to her cousin’s country cottage. It was dark outside, and the visibility was poor. She had planned to arrive before sunset, but the rental service had made a mistake, and it took hours before she got her rental car at the airport. It was past midnight now, and after a long day of traveling, Sarah was starting to get sleepy.

    Fortunately, there were only 15 km to go, but her eyelids were starting to feel heavy. To stay awake, she put her favorite CD on, turned up the volume, and started to sing along. This seemed to help a little -good- only 10 km to go. This was when Sarah’s phone started ringing, and she awkwardly tried to find the mute button for the car stereo while answering the phone. As she looked up again, she barely caught a glimpse of the red brake lights of the car in front of her as she smashed into it.

  • 72.
    Ahlström, Christer
    et al.
    Swedish National Road and Transport Research Institute, Traffic and road users, Human-vehicle-transport system interaction.
    Kircher, Katja
    Swedish National Road and Transport Research Institute, Traffic and road users, Human-vehicle-transport system interaction.
    Kircher, Albert
    Linköpings Universitet.
    A gaze-based driver distraction warning system and its effect on visual behaviour2013In: IEEE transactions on intelligent transportation systems (Print), ISSN 1524-9050, E-ISSN 1558-0016, Vol. 14, no 2, p. 965-973Article in journal (Refereed)
    Abstract [en]

    Driver distraction is a contributing factor to many crashes; therefore, a real-time distraction warning system should have the potential to mitigate or circumvent many of these crashes. The objective of this paper is to investigate the usefulness of a real-time distraction detection algorithm called AttenD. The evaluation is based on data from an extended field study comprising seven drivers who drove on an average of 4351 ± 2181 km in a naturalistic setting.

    Visual behavior was investigated both on a global scale and on a local scale in the surroundings of each warning. An increase in the percentage of glances at the rear-view mirror and a decrease in the amount of glances at the center console were found. The results also show that visual time sharing decreased in duration from 9.94 to 9.20 s due to the warnings, that the time from fully attentive to warning decreased from 3.20 to 3.03 s, and that the time from warning to full attentiveness decreased from 6.02 to 5.46 s. The limited number of participants does not allow any generalizable conclusions, but a trend toward improved visual behavior could be observed. This is a promising start for further improvements of the algorithm and the warning strategy.

  • 73.
    Ahlström, Christer
    et al.
    Swedish National Road and Transport Research Institute, Traffic and road users, Human-vehicle-transport system interaction.
    Kircher, Katja
    Swedish National Road and Transport Research Institute, Traffic and road users, Human-vehicle-transport system interaction.
    Kircher, Albert
    Swedish National Road and Transport Research Institute, Traffic and road users, Vehicle technology and simulation.
    Considerations when calculating percent road centre from eye movement data in driver distraction monitoring2009In: Proceedings of the Fifth International Driving Symposium on Human Factors in Driver Assessment, Training and Vehicle Design, 2009, p. 132-139Conference paper (Refereed)
    Abstract [en]

    Percent road center (PRC) is a performance indicator which is sensitive to driver distraction. The original definition of PRC is based on fixation data extracted from eye movement recordings, but it has also been suggested that PRC can be determined directly from the gaze data without segmenting it into saccades and fixations. The primary aim of this paper is to investigate if this is the case.

    Naturalistic driving data from a small scale field operational test comprising seven vehicles was used in the evaluation. It was found that PRC time traces based on gaze data and fixation data, respectively, were highly similar (correlation coefficient=0.95, average wavelet semblance=0.84) except for an absolute amplitude difference of about 8%. This indicates that the two approaches can be used interchangeably and that the processing step of segmenting gaze data into saccades and fixations can be left out.

    In addition to this finding, design issues related to the calculation of PRC are investigated. Especially, the impact of gaze cases pointing towards the intersection of the road centre area and the centre rear mirror were investigated. Results lead to conclude that gazes and fixations on the centre rear mirror should be removed from the PRC calculations, as they may negatively influence the correctness of the performance indicator.

  • 74.
    Ahlström, Christer
    et al.
    Swedish National Road and Transport Research Institute, Traffic and road users, Human-vehicle-transport system interaction.
    Kircher, Katja
    Swedish National Road and Transport Research Institute, Traffic and road users, Human-vehicle-transport system interaction.
    Rydström, Annie
    Volvo Car Corperation.
    Nåbo, Arne
    SAAB Automobile.
    Almgren, Susanne
    SAAB Automobile.
    Ricknäs, Daniel
    Scania.
    Effects of visual, cognitive and haptic tasks on driving performance indicators2012In: Advances in Human Aspects of Road and Rail Transportation / [ed] Neville A . Stanton, San Francisco, USA: CRC Press , 2012, p. 673-682Conference paper (Refereed)
    Abstract [en]

    A driving simulator study was conducted by using the same setup in two driving simulators, one with a moving base and one with a fixed base. The aim of the study was to investigate a selection of commonly used performance indicators (PIs) for their sensitivity to secondary tasks loading on different modalities and levels of difficulty, and to evaluate their robustness across simulator platforms. The results showed that, across platforms, the longitudinal PIs behaved similarly whereas the lateral control and eye movement based performance indicators differed. For modality, there were considerable effects on lateral, longitudinal as well as eye movement PIs. However, there were only limited differences between the baseline and the cognitive and haptic tasks. For difficulty, clear effects on PIs related to lateral control and eye movements were shown. Additionally, it should be noted that there were large individual differences for several of the PIs. In conclusion, many of the most commonly used PIs are susceptible to individual differences, and, especially the PIs for lateral control, to the platform and environment where they are acquired, which is why generalizations should be made with caution.

  • 75.
    Ahlström, Christer
    et al.
    Swedish National Road and Transport Research Institute, Traffic and road users, Human-vehicle-transport system interaction.
    Kircher, Katja
    Swedish National Road and Transport Research Institute, Traffic and road users, Human-vehicle-transport system interaction.
    Thorslund, Birgitta
    Swedish National Road and Transport Research Institute, Traffic and road users, Human-vehicle-transport system interaction.
    Adell, Emeli
    Trivector Traffic.
    Bicyclists’ visual strategies when conducting self-paced vs. system-paced smartphone tasks in traffic2015In: Transportation Research Part F: Traffic Psychology and Behaviour, ISSN 1369-8478, E-ISSN 1873-5517, Vol. 41, p. 204-216Article in journal (Refereed)
    Abstract [en]

    Visual distraction among cyclists interacting with their mobile phones is a growing concern. Yet, very little research has actually investigated how cyclists apply visual strategies and adapt task execution depending on the traffic situation. The aim of this study is to investigate visual behaviour of cyclists when conducting self-paced (initiated by the cyclist) vs. system-paced (initiated by somebody else) smartphone tasks in traffic. Twenty-two cyclists completed a track in real traffic while listening to music, receiving and making calls, receiving and sending text messages, and searching for information on the internet. The route and the types of tasks were controlled, but the cyclists could choose rather freely when and where along the route to carry out the tasks, thus providing semi-naturalistic data on compensatory behaviour. The results show that the baseline and music conditions were similar in terms of visual behaviour. When interacting with the phone, it was found that glances towards the phone mostly came at the expense of glances towards traffic irrelevant gaze targets and also led to shortened glance durations to traffic relevant gaze targets, while maintaining the number of glances. This indicates that visual “spare capacity” is used for the execution of the telephone tasks. The task type influenced the overall task duration and the overall glance intensity towards the phone, but not the mean nor maximum duration of individual glances. Task pacing was the factor that influenced visual behaviour the most, with longer mean and maximum glance durations for self-paced tasks. In conclusion, the cyclists used visual strategies to integrate the handling of mobile phones into their cycling behaviour. Glances directed towards the phone did not lead to traffic relevant gaze targets being missed. In system-paced scenarios, the cyclists checked the traffic more frequently and intensively than in self-paced tasks. This leads to the assumption that cyclists prepare for self-initiated tasks by for example choosing a suitable location. Future research should investigate whether these strategies also exists amongst drivers and other road user groups.

  • 76.
    Ahlström, Christer
    et al.
    Swedish National Road and Transport Research Institute, Traffic and road users, Human-vehicle-transport system interaction.
    Nyström, Marcus
    Lunds Universitet.
    Holmqvist, Kenneth
    Lunds Universitet.
    Fors, Carina
    Swedish National Road and Transport Research Institute, Traffic and road users, Human-vehicle-transport system interaction.
    Sandberg, David
    Swedish National Road and Transport Research Institute, Traffic and road users, Human-vehicle-transport system interaction.
    Anund, Anna
    Swedish National Road and Transport Research Institute, Traffic and road users, Human-vehicle-transport system interaction.
    Kecklund, Göran
    Stockholms Universitet.
    Ņkerstedt, Torbjörn
    Stockholms Universitet.
    Fit-for-duty test for estimation of drivers’ sleepiness level: Eye movements improve the sleep/wake predictor2013In: Transportation Research Part C: Emerging Technologies, ISSN 0968-090X, E-ISSN 1879-2359, Vol. 26, p. 20-32Article in journal (Refereed)
    Abstract [en]

    Driver sleepiness contributes to a considerable proportion of road accidents, and a fit-for-duty test able to measure a driver’s sleepiness level might improve traffic safety. The aim of this study was to develop a fit-for-duty test based on eye movement measurements and on the sleep/wake predictor model (SWP, which predicts the sleepiness level) and evaluate the ability to predict severe sleepiness during real road driving. Twenty-four drivers participated in an experimental study which took place partly in the laboratory, where the fit-for-duty data were acquired, and partly on the road, where the drivers sleepiness was assessed. A series of four measurements were conducted over a 24-h period during different stages of sleepiness. Two separate analyses were performed; a variance analysis and a feature selection followed by classification analysis. In the first analysis it was found that the SWP and several eye movement features involving anti-saccades, pro-saccades, smooth pursuit, pupillometry and fixation stability varied significantly with different stages of sleep deprivation. In the second analysis, a feature set was determined based on floating forward selection. The correlation coefficient between a linear combination of the acquired features and subjective sleepiness (Karolinska sleepiness scale, KSS) was found to be R=. 0.73 and the correct classification rate of drivers who reached high levels of sleepiness (KSS ≥ 8) in the subsequent driving session was 82.4% (sensitivity = 80.0%, specificity = 84.2% and AUC = 0.86). Future improvements of a fit-for-duty test should focus on how to account for individual differences and situational/contextual factors in the test, and whether it is possible to maintain high sensitive/specificity with a shorter test that can be used in a real-life environment, e.g. on professional drivers. © 2012 Elsevier Ltd.

  • 77.
    Ahlström, Christer
    et al.
    Swedish National Road and Transport Research Institute, Traffic and road users, Human-vehicle-transport system interaction.
    Victor, Trent
    Chalmers University of Technology.
    Wege, Claudia
    Steinmetz, Erik
    SP Technical Research Institute Sweden.
    Processing of eye/head-tracking data in large-scale naturalistic driving data sets2012In: IEEE transactions on intelligent transportation systems (Print), ISSN 1524-9050, E-ISSN 1558-0016, Vol. 13, no 2, p. 553-564Article in journal (Refereed)
    Abstract [en]

    Driver distraction and driver inattention are frequently recognized as leading causes of crashes and incidents. Despite this fact, there are few methods available for the automatic detection of driver distraction. Eye tracking has come forward as the most promising detection technology, but the technique suffers from quality issues when used in the field over an extended period of time. Eye-tracking data acquired in the field clearly differs from what is acquired in a laboratory setting or a driving simulator, and algorithms that have been developed in these settings are often unable to operate on noisy field data. The aim of this paper is to develop algorithms for quality handling and signal enhancement of naturalistic eye- and head-tracking data within the setting of visual driver distraction. In particular, practical issues are highlighted. Developed algorithms are evaluated on large-scale field operational test data acquired in the Sweden-Michigan Field Operational Test (SeMiFOT) project, including data from 44 unique drivers and more than 10000 trips from 13 eye-tracker-equipped vehicles. Results indicate that, by applying advanced data-processing methods, sensitivity and specificity of eyes-off-road glance detection can be increased by about 10%. In conclusion, postenhancement and quality handling is critical when analyzing large databases with naturalistic eye-tracking data. The presented algorithms provide the first holistic approach to accomplish this task. © 2011 IEEE.

  • 78.
    Ahlström, Christer
    et al.
    Swedish National Road and Transport Research Institute, Traffic and road users, Human Factors in the Transport System.
    Wachtmeister, Jesper
    Mobile Behaviour.
    Nyman, Mattias
    Designingenjörerna Sverige AB.
    Nordenström, Axel
    Designingenjörerna Sverige AB.
    Kircher, Katja
    Swedish National Road and Transport Research Institute, Traffic and road users, Human Factors in the Transport System.
    Using smartphone logging to gain insight about phone use in traffic2019In: Cognition, Technology & Work, ISSN 1435-5558, E-ISSN 1435-5566Article in journal (Refereed)
    Abstract [en]

    The prevalence of mobile phone usage in traffic has been studied by road-side counting, naturalistic driving data, surveillance cameras, smartphone logging, and subjective estimates via surveys. Here, we describe a custom-made smartphone logging application along with suggestions on how future such applications should be designed. The developed application logs’ start and end times of all phone interactions (mobile phone applications, incoming/outgoing phone calls and text messages, audio output, and screen activations). In addition, all movements are automatically classified into transport, cycling, walking, running, or stationary. The capabilities of the approach are demonstrated in a pilot study with 143 participants. Examples of results that can be gained from smartphone logging include prevalence in different transportation modes (here found to be 12% while driving, 4% while cycling, and 7% while walking), which apps are being used (here found to be 19% navigation, 12% talking, 12% social media, and 10% games) and on which road types (rural, urban, highway etc.). Smartphone logging was found to be an insightful complement to the other methods for assessing phone use in traffic, especially since it allows the analyses of which apps are used and where they are used, split into transportation mode and road type, all at a relatively low cost.

  • 79.
    Ahmad, Numan
    et al.
    National University of Sciences and Technology, Pakistan.
    Ahmed, Anwaar
    National University of Sciences and Technology, Pakistan.
    Shah, Akhtar Ali
    University of Peshawar.
    Effectiveness of enforcement of seatbelt law: an exploratory empirical analysis using aggregate data2018Conference paper (Refereed)
    Abstract [en]

    Increasing motorization has enhanced the risk of road traffic crashes worldwide. Enforcing legislation on key risk factors such as seatbelt use by vehicle occupants is critical in reduction of road crash fatalities and injuries. This study estimated an ordered probit model to explore the relationship between effectiveness of enforcement of seatbelt law and different exploratory variables using data from World Health Organization. This study categorizes the enforcement of seatbelt law into four different levels including very low, low, medium and high. Through this study an attempt has been made to establish the relationship between effectiveness of enforcement of seat belt laws and socio-economic conditions, road crash fatalities, road safety legislation and public policies. Model results revealed that effectiveness of enforcement of seat belt law is significantly associated with road crash fatalities per thousand registered vehicles, legislation on cell phone use while driving, availability of training in emergency medicine for doctors, existence of national or sub-national policy for promoting walking and cycling, the existence of funded lead agency and maximum speed limit on rural road of a country. This research aims to provide a preliminary insight to planners and enforcement agencies to identify significance of seatbelt enforcement and suggest measures compatible to the typical socio-cultural and institutional set up for making the roads safer.

  • 80.
    Ahmed, Abubeker
    et al.
    Swedish National Road and Transport Research Institute, Infrastructure, Pavement Technology.
    Carlsson, Håkan
    Swedish National Road and Transport Research Institute, Infrastructure, Measurement technology and engineering workshop.
    Lundberg, Thomas
    Swedish National Road and Transport Research Institute, Infrastructure, Infrastructure maintenance.
    Utvärdering av gummiasfalt: provväg E22 Mönsterås : etapp 12019Report (Other academic)
    Abstract [en]

    Laboratory and filed investigations have been carried out to evaluate the performance of rubber modified asphalt test road on E22 Mönsterås.

    The laboratory investigations indicated that there are no significant differences in stiffness and shear modulus between the reference and rubber modified mixtures. The rubber modified mixture however showed slightly lower phase angle compared to the reference mixture which indicate that the rubber modified mixture is more elastic. The rubber modified mixtures also showed lower modulus at lower temperatures and slightly higher modulus at higher temperature which are desired properties for resistance against low temperature cracking and permanent deformation respectively. The fatigue tests indicated that the rubber modified asphalt mixture has slightly better fatigue cracking performance. But the difference is not significant.

    The road surface profile measurements indicated no significant differences between the reference and asphalt rubber sections. It is however early to draw conclusions after one year of traffic therefore additional follow-up of the test sections is needed to draw a conclusion.

  • 81.
    Ahmed, Abubeker
    et al.
    Swedish National Road and Transport Research Institute, Infrastructure, Pavement Technology.
    Hellman, Fredrik
    Swedish National Road and Transport Research Institute, Infrastructure, Pavement Technology.
    Erlingsson, Sigurdur
    Swedish National Road and Transport Research Institute, Infrastructure, Pavement Technology.
    Full scale accelerated pavement tests to evaluate the performance of permeable and skeletal soil block pavement systems2016In: The Roles of Accelerated Pavement Testing in Pavement Sustainability: Engineering, Environment, and Economics, Springer International Publishing , 2016, p. 131-144Chapter in book (Other academic)
    Abstract [en]

    The increasing proportion of paved surface due to urbanization means that the conditions for urban trees and vegetation to survive have deteriorated. Factors such as air pollution, poor drainage, and the lack of usable soil for root growth contribute to the short life expectancy of urban trees. To meet this challenge, several permeable and "structural" or "skeletal soils" have been developed as alternatives to the typical compacted soil required to bear the weight of vehicular traffic in urban areas. The main objective of this study is to evaluate the resistance to permanent deformation of permeable and skeletal soil pavement structures based on full scale accelerated pavement tests (APT) using a heavy vehicle simulator (HVS). Interlocking paving stones of various types were used as permeable surface layer for the test structures. The results demonstrated that the permeable test structures exhibited higher permanent deformation than the corresponding impervious structures. The skeletal soil with bituminous base layer, however, produced performance comparable to the impervious reference test structures.

  • 82.
    Ahmed, Abubeker W.
    Swedish National Road and Transport Research Institute, Infrastructure, Pavement Technology. KTH.
    Mechanistic-Empirical Modelling of Flexible Pavement Performance: Verifications Using APT Measurements2014Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Mechanistic-Empirical  (M-E)  pavement  design  procedures  are  composed  of  a  reliable  response model to estimate the state of stress in the pavement and distress models in order to predict the different types of pavement distresses due to the prevailing traffic and environmental conditions. One of the main objectives of this study was to develop a response model based on multilayer elastic  theory   (MLET)  with  improved  computational  performance  by   optimizing  the   time consuming parts of the MLET processes. A comprehensive comparison of the developed program with  two  widely  used  programs  demonstrated  excellent  agreement  and  improved  computational performance.  Moreover,  the  program  was  extended  to  incorporate  the  viscoelastic  behaviour  of bituminous materials through elastic-viscoelastic correspondence principle. A procedure based on collocation of linear viscoelastic (LVE) solutions at selected key time durations was also proposed that improved the computational performance for LVE analysis of stationary and moving loads. A comparison  of  the  LVE  responses  with  measurements  from  accelerated  pavement  testing  (APT) revealed a good agreement. Furthermore the developed response model was employed to evaluate permanent deformation models  for  bound  and  unbound  granular  materials  (UGMs)  using  full  scale  APTs.  The  M-E Pavement  Design  Guide  (MEPDG)  model  for  UGMs  and  two  relatively  new  models  were evaluated  to  model  the  permanent  deformation  in  UGMs.  Moreover,  for  bound  materials,  the simplified  form  of  the  MEPDG  model  for  bituminous  bound  layers  was  also  evaluated.  The measured  and  predicted  permanent  deformations  were  in  general  in  good  agreement,  with  only small discrepancies between the models. Finally, as heavy traffic loading is one of the main factors affecting the performance of flexible pavement, three types of characterizations for heavy traffic axle load spectrum for M-E analysis and design of pavement structures were evaluated. The study recommended an improved approach that enhanced the accuracy and computational performance.

    List of papers
    1. Evaluation of permanent deformation models for unbound granular materials using accelerated pavement tests
    Open this publication in new window or tab >>Evaluation of permanent deformation models for unbound granular materials using accelerated pavement tests
    2013 (English)In: International Journal on Road Materials and Pavement Design, ISSN 1468-0629, E-ISSN 2164-7402, Vol. 14, no 1, p. 178-195Article in journal (Refereed) Published
    Abstract [en]

    Mechanistic-empirical (M-E) pavement design methods have become the focus of modern pavement design procedure. One of the main distresses that M-E design methods attempt to control is permanent deformation (rutting). The objective of this paper is to evaluate three M-E permanent deformation models for unbound granular materials, one from the US M-E pavement design guide and two other relatively new models. Two series of heavy vehicle simulator (HVS) tests with three different types of base material were used for this purpose. The permanent deformation, wheel loading, pavement temperature, and other material properties were continuously controlled during the HVS tests. Asphalt concrete layers were considered as linear elastic where stress-dependent behaviour of unbound materials was considered when computing responses for the M-E permanent deformation models with a nonlinear elastic response model. Traffic wandering was also accounted for in modelling the traffic by assuming it was normally distributed and a time-hardening approach was applied to add together the permanent deformation contributions from different stress levels. The measured and predicted permanent deformations are in general in good agreement with only small discrepancies between the models. Model parameters were also estimated for three different types of material.

    Place, publisher, year, edition, pages
    Taylor & Francis Group, 2013
    Keywords
    Rutting (wheel), Unbound base, Granular, Stress (in material)
    National Category
    Infrastructure Engineering
    Research subject
    Road: Highway design, Road: Pavement design; Road: Materials, Road: Aggregate and stone materials
    Identifiers
    urn:nbn:se:vti:diva-6941 (URN)10.1080/14680629.2012.755936 (DOI)
    Available from: 2014-07-17 Created: 2014-07-17 Last updated: 2017-12-05Bibliographically approved
    2. Modeling of flexible pavement structure behavior: Comparisons with Heavy Vehicle Simulator measurements
    Open this publication in new window or tab >>Modeling of flexible pavement structure behavior: Comparisons with Heavy Vehicle Simulator measurements
    2012 (English)In: Advances in Pavement Design Through Full-Scale Accelerated Pavement Testing / [ed] Jones, Harvey, Mateos & Al-Qadi, London: Taylor & Francis Group, 2012, p. 493-503Conference paper, Published paper (Refereed)
    Abstract [en]

     A response model to be employed in a mechanistic-empirical pavement performance predictionmodel based on multilayer elastic theory has been developed. An iterative approach using a method of successiveover-relaxation of a stress dependency model is used to account for the nonlinear behavior of unbound materials. Asphalt and subgrade materials are assumed to be linear elastic. The response model was verified against two series of Heavy Vehicle Simulator (HVS) response measurements made under a variety of wheel loadconfigurations and at different pavement temperatures. A comparison with Falling Weight Deflectometer (FWD)data was also carried out. The model was subsequently used to predict permanent deformation from the HVS testing using simple work hardening models. A time hardening approach has been adopted to combine permanentdeformation contributions from stress levels of different magnitude.The response model outputs and the predictedpermanent deformations were generally in good agreement with the measurements.

    Place, publisher, year, edition, pages
    London: Taylor & Francis Group, 2012
    Keywords
    Pavement, Simulation, Deflectograph, Model
    National Category
    Civil Engineering
    Research subject
    Road: Highway design, Road: Pavement design
    Identifiers
    urn:nbn:se:vti:diva-6942 (URN)10.1201/b13000-61 (DOI)ISBN 978-0-415-62138-0 (ISBN)
    Conference
    The 4th International Conference on Accelerated Pavement Testing
    Available from: 2014-07-17 Created: 2014-07-17 Last updated: 2014-08-22Bibliographically approved
    3. Fast layered elastic response program for the analysis of flexible pavement structures
    Open this publication in new window or tab >>Fast layered elastic response program for the analysis of flexible pavement structures
    2013 (English)In: International Journal on Road Materials and Pavement Design, ISSN 1468-0629, E-ISSN 2164-7402, Vol. 14, no 1, p. 196-210Article in journal (Refereed) Published
    Abstract [en]

    One of the key components in analysing pavement structural behaviour is the response model which is used to estimate the stresses, strains and displacements of the pavement structure subjected to the existing traffic, taking into account the material properties and prevailing environmental conditions. Multilayer elastic theory (MLET) is often preferred over other methods such as the finite element method, due to its computational performance for repeated applications. A new elastic response analysis program has been developed based on the Burmister MLET theory to calculate the response of flexible pavement structures. In the development of the program, the time-consuming part of MLET processes was optimised. To improve the convergence and accuracy of responses in the vicinity of the surface of the top layer, an approach based on Richardson's extrapolation was employed. Moreover, an iterative approach to model stress dependency of unbound granular materials was incorporated. A comprehensive comparison of the program with two frequently used programs demonstrated an excellent agreement and improved performance.

    Place, publisher, year, edition, pages
    Taylor & Francis Group, 2013
    Keywords
    Elasticity, Flexible pavement, Model (not math)
    National Category
    Civil Engineering
    Research subject
    Road: Highway design, Road: Surfacing
    Identifiers
    urn:nbn:se:vti:diva-6944 (URN)10.1080/14680629.2012.757558 (DOI)
    Available from: 2014-07-17 Created: 2014-07-17 Last updated: 2017-12-05Bibliographically approved
    4. Characterization of heavy traffic axle load spectra for mechanistic-empirical pavement design applications
    Open this publication in new window or tab >>Characterization of heavy traffic axle load spectra for mechanistic-empirical pavement design applications
    2015 (English)In: The international journal of pavement engineering, ISSN 1029-8436, E-ISSN 1477-268X, Vol. 16, no 6, p. 488-501Article in journal (Refereed) Published
    Abstract [en]

     Heavy traffic axle load spectrum (ALS) is  one of the key inputs for mechanistic-empirical analysis and design of pavement structures. Frequently, the entire ALS is aggregated into Equivalent Number of Single Axle Loads (ESAL) or assumed to have Constant Contact  Area  (CCA)  or  Constant  Contact  Pressure  (CCP).  These characterizations affect the accuracy and computational performance of the pavement analysis. The objective of this study was to evaluate these  characterizations  based  on  predicted  performances  to  rutting and fatigue cracking of several pavement structures subjected to ALS data collected from 12 Bridge-Weigh-In-Motion stations. The results indicated  that  for  layers  below  the  top  25  cm,  all  characterizations produced similar values of predicted rutting. However, for the top 25 cm, the methods differed in the predicted performances to rutting and fatigue cracking. Furthermore an improvement to the CCA approach was proposed that enhanced the accuracy while maintaining the same level of computational performance.

    Place, publisher, year, edition, pages
    Taylor & Francis Group, 2015
    Keywords
    Axle load, Heavy vehicle, Pavement design, Rutting, Cracking, Prediction, Accuracy
    National Category
    Infrastructure Engineering
    Research subject
    30 Road: Highway design, 32 Road: Pavement design
    Identifiers
    urn:nbn:se:vti:diva-6945 (URN)10.1080/10298436.2014.943131 (DOI)000354458200003 ()2-s2.0-84929283717 (Scopus ID)
    Available from: 2014-07-17 Created: 2014-07-17 Last updated: 2017-12-05Bibliographically approved
    5. Viscoelastic modelling of pavement structure behaviour in a full scale accelerated pavement test
    Open this publication in new window or tab >>Viscoelastic modelling of pavement structure behaviour in a full scale accelerated pavement test
    (English)Manuscript (preprint) (Other academic)
    Keywords
    Viscoelasticity, Full scale, Flexible pavement, Test, Performance, Deformation, Model (not math), Rutting (wheel)
    National Category
    Civil Engineering
    Research subject
    30 Road: Highway design, 32 Road: Pavement design
    Identifiers
    urn:nbn:se:vti:diva-6947 (URN)
    Available from: 2014-07-17 Created: 2014-07-17 Last updated: 2016-01-11Bibliographically approved
    6. Evaluation of permanent deformation model for asphalt concrete mixtures by means of extra-large wheel tracking and full scale accelerated pavement tests
    Open this publication in new window or tab >>Evaluation of permanent deformation model for asphalt concrete mixtures by means of extra-large wheel tracking and full scale accelerated pavement tests
    (English)Manuscript (preprint) (Other academic)
    Keywords
    Rutting, Deformation, Bituminous mixture, Flexible pavement, Mathematical model, Full scale, Test
    National Category
    Civil Engineering
    Research subject
    30 Road: Highway design, 32 Road: Pavement design
    Identifiers
    urn:nbn:se:vti:diva-6949 (URN)
    Available from: 2014-07-17 Created: 2014-07-17 Last updated: 2016-01-25Bibliographically approved
  • 83.
    Ahmed, Abubeker W.
    et al.
    Swedish National Road and Transport Research Institute, Infrastructure, Pavement Technology.
    Biligiri, Krishna Prapoorna
    Department of Civil Engineering Indian Institute of Technology Kharagpur .
    Hakim, Hassan
    Swedish National Road and Transport Research Institute, Infrastructure, Pavement Technology.
    An Algorithm to Estimate Rational Values of Phase Angles and Moduli of Asphalt Mixtures2013In: International Journal of Pavement Research and Technology (IJPRT), ISSN ISSN 1997-1400, Vol. 6, no 6, p. 745-754Article in journal (Refereed)
    Abstract [en]

    The objective of this study was to develop and evaluate an algorithm based on Fast Fourier Transform (FFT) that can calculate rational values of phase angle (f) and moduli of the variants of asphalt mixtures for the data obtained from the different frequency sweep tests. f and moduli for ten different asphalt mixtures resulting in over 690 data points collected from both USA and Sweden were computed using FFT. Theoretical observations revealed that there were significant differences for f between FFT and other methods to the order of 10-50%; however, there was no difference in moduli estimates for any mix and was independent of the test. Precisely, the FFT method produced rational f for mixtures that deviate from conventional mixture properties. Furthermore, statistical comparisons corroborated the predicted f estimates indicative of significant differences between the analysis techniques; but, the moduli were unaffected by the analysis methods. The study successfully illustrated the FFT technique, a user-friendly analytical procedure that can obviate the errors in the rational estimation of the acutely sensitive viscoelastic parameters.

  • 84.
    Ahmed, Abubeker W.
    et al.
    Swedish National Road and Transport Research Institute, Infrastructure, Pavement Technology.
    Erlingsson, Sigurdur
    Swedish National Road and Transport Research Institute, Infrastructure, Pavement Technology.
    Characterization of heavy traffic axle load spectra for mechanistic-empirical pavement design applications2015In: The international journal of pavement engineering, ISSN 1029-8436, E-ISSN 1477-268X, Vol. 16, no 6, p. 488-501Article in journal (Refereed)
    Abstract [en]

     Heavy traffic axle load spectrum (ALS) is  one of the key inputs for mechanistic-empirical analysis and design of pavement structures. Frequently, the entire ALS is aggregated into Equivalent Number of Single Axle Loads (ESAL) or assumed to have Constant Contact  Area  (CCA)  or  Constant  Contact  Pressure  (CCP).  These characterizations affect the accuracy and computational performance of the pavement analysis. The objective of this study was to evaluate these  characterizations  based  on  predicted  performances  to  rutting and fatigue cracking of several pavement structures subjected to ALS data collected from 12 Bridge-Weigh-In-Motion stations. The results indicated  that  for  layers  below  the  top  25  cm,  all  characterizations produced similar values of predicted rutting. However, for the top 25 cm, the methods differed in the predicted performances to rutting and fatigue cracking. Furthermore an improvement to the CCA approach was proposed that enhanced the accuracy while maintaining the same level of computational performance.

  • 85.
    Ahmed, Abubeker W.
    et al.
    Swedish National Road and Transport Research Institute, Infrastructure, Pavement Technology.
    Erlingsson, Sigurdur
    Swedish National Road and Transport Research Institute, Infrastructure, Pavement Technology.
    Evaluation of a permanent deformation model for asphalt concrete mixtures using extra-large wheel-tracking and heavy vehicle simulator tests2015In: International Journal on Road Materials and Pavement Design, ISSN 1468-0629, E-ISSN 2164-7402, Vol. 16, no 1, p. 154-171Article in journal (Refereed)
    Abstract [en]

    This paper evaluates a mechanistic–empirical permanent strain model for asphalt concrete mixtures. The evaluation was carried out based on two different types of tests: an extra-large wheel-tracking (ELWT) test and a full-scale accelerated pavement test using a heavy vehicle simulator (HVS). Asphalt slabs from three different types of asphalt mixtures were prepared for the ELWT test and tested at several pavement temperatures and tyre inflation pressures. Lateral wandering was also incorporated.

    The measured permanent deformations in the asphalt slabs were thereafter modelled using the permanent strain model from the US Mechanistic-Empirical Pavement Design Guide and model parameters were estimated for the three types of mixes. For validation, data from an HVS tested pavement structure consisting of the same asphalt mixtures as those tested using the ELWT were used. A set of calibration factors for the three mixtures were therefore obtained between the two tests. In all cases, the calibration factors were within ±20% from unity. Differences in geometry, scale, wheel loading configuration as well as the speed of loading between the two test devices could be the possible reasons for the differences in observed calibration factors.

  • 86.
    Ahmed, Abubeker W.
    et al.
    Swedish National Road and Transport Research Institute, Infrastructure, Pavement Technology.
    Erlingsson, Sigurdur
    Swedish National Road and Transport Research Institute, Infrastructure, Pavement Technology.
    Evaluation of permanent deformation model for asphalt concrete mixtures by means of extra-large wheel tracking and full scale accelerated pavement testsManuscript (preprint) (Other academic)
  • 87.
    Ahmed, Abubeker W.
    et al.
    Swedish National Road and Transport Research Institute, Infrastructure, Pavement Technology.
    Erlingsson, Sigurdur
    Swedish National Road and Transport Research Institute, Infrastructure, Pavement Technology.
    Evaluation of permanent deformation models for unbound granular materials using accelerated pavement tests2013In: International Journal on Road Materials and Pavement Design, ISSN 1468-0629, E-ISSN 2164-7402, Vol. 14, no 1, p. 178-195Article in journal (Refereed)
    Abstract [en]

    Mechanistic-empirical (M-E) pavement design methods have become the focus of modern pavement design procedure. One of the main distresses that M-E design methods attempt to control is permanent deformation (rutting). The objective of this paper is to evaluate three M-E permanent deformation models for unbound granular materials, one from the US M-E pavement design guide and two other relatively new models. Two series of heavy vehicle simulator (HVS) tests with three different types of base material were used for this purpose. The permanent deformation, wheel loading, pavement temperature, and other material properties were continuously controlled during the HVS tests. Asphalt concrete layers were considered as linear elastic where stress-dependent behaviour of unbound materials was considered when computing responses for the M-E permanent deformation models with a nonlinear elastic response model. Traffic wandering was also accounted for in modelling the traffic by assuming it was normally distributed and a time-hardening approach was applied to add together the permanent deformation contributions from different stress levels. The measured and predicted permanent deformations are in general in good agreement with only small discrepancies between the models. Model parameters were also estimated for three different types of material.

  • 88.
    Ahmed, Abubeker W
    et al.
    Swedish National Road and Transport Research Institute, Infrastructure, Pavement Technology.
    Erlingsson, Sigurdur
    Swedish National Road and Transport Research Institute, Infrastructure, Pavement Technology.
    Mechanistic modelling of HVS flexible pavement structure2012In: EPAM 2012: Malmö, Sweden, 5–7 September: 4th European pavement and asset management conference, Linköping: Statens väg- och transportforskningsinstitut, 2012, , p. 13Conference paper (Other (popular science, discussion, etc.))
    Abstract [en]

    A response model to be employed in a mechanistic-empirical pavement performance prediction model based on multilayer elastic theory has been developed. An iterative approach using a method of successive over-relaxation of stress dependency model is used to account for the nonlinear behaviour of unbound materials. Asphalt and subgrade materials are assumed as linear elastic. The response model is verified using heavy vehicle simulator (HVS) response measurements made under variety of wheel load configurations and at different pavement temperatures. The permanent deformation behaviours of the HVS structure is also modelled using mechanistic empirical approach and by employing permanent deformation prediction models. A time hardening approach has been applied to combine permanent deformation contributions from stress levels of different magnitude. The response model outputs and the predicted permanent deformations are in general in good agreement with the measurements.

  • 89.
    Ahmed, Abubeker W.
    et al.
    Swedish National Road and Transport Research Institute, Infrastructure, Pavement Technology.
    Erlingsson, Sigurdur
    Swedish National Road and Transport Research Institute, Infrastructure, Pavement Technology.
    Modeling of flexible pavement structure behavior: Comparisons with Heavy Vehicle Simulator measurements2012In: Advances in Pavement Design Through Full-Scale Accelerated Pavement Testing / [ed] Jones, Harvey, Mateos & Al-Qadi, London: Taylor & Francis Group, 2012, p. 493-503Conference paper (Refereed)
    Abstract [en]

     A response model to be employed in a mechanistic-empirical pavement performance predictionmodel based on multilayer elastic theory has been developed. An iterative approach using a method of successiveover-relaxation of a stress dependency model is used to account for the nonlinear behavior of unbound materials. Asphalt and subgrade materials are assumed to be linear elastic. The response model was verified against two series of Heavy Vehicle Simulator (HVS) response measurements made under a variety of wheel loadconfigurations and at different pavement temperatures. A comparison with Falling Weight Deflectometer (FWD)data was also carried out. The model was subsequently used to predict permanent deformation from the HVS testing using simple work hardening models. A time hardening approach has been adopted to combine permanentdeformation contributions from stress levels of different magnitude.The response model outputs and the predictedpermanent deformations were generally in good agreement with the measurements.

  • 90.
    Ahmed, Abubeker W.
    et al.
    Swedish National Road and Transport Research Institute, Infrastructure, Pavement Technology.
    Erlingsson, Sigurdur
    Swedish National Road and Transport Research Institute, Infrastructure, Pavement Technology.
    Numerical validation of viscoelastic responses of a pavement structure in a full-scale accelerated pavement test2015In: The international journal of pavement engineering, ISSN 1029-8436, E-ISSN 1477-268XArticle in journal (Refereed)
    Abstract [en]

    This paper demonstrates the application of a generalised layered linear viscoelastic (LVE) analysis for estimating the structural response of flexible pavements. A comparison of the direct layered viscoelastic responses with approximate solutions based on the linear elastic (LE) and LVE collocation methods was also carried out. The different approaches were implemented by extending a layered elastic program with an improved computational performance. The LE and LVE collocation methods were further extended for analysis of pavements under moving loads.

    The methods were illustrated by analysing a pavement structure subjected to moving wheel loads of 30, 50, 60 and 80 kN using a Heavy Vehicle Simulator (HVS). The various responses (stresses and strains) in the pavement, at pavement temperatures of 0, 10 and 20°C, were measured using various types of sensors installed in the structure. It was shown that the approximated LVE solution based on the LE collocation method agreed very well with the measurements and is computationally the least expensive.

  • 91.
    Ahmed, Abubeker W.
    et al.
    Swedish National Road and Transport Research Institute, Infrastructure, Pavement Technology. Kungliga Tekniska Högskolan.
    Erlingsson, Sigurdur
    Swedish National Road and Transport Research Institute, Infrastructure, Pavement Technology. Kungliga Tekniska Högskolan.
    Viscoelastic modelling of pavement structure behaviour in a full scale accelerated pavement testManuscript (preprint) (Other academic)
  • 92.
    Ahmed, Abubeker W
    et al.
    Swedish National Road and Transport Research Institute, Infrastructure, Pavement Technology.
    Erlingsson, Sigurdur
    Swedish National Road and Transport Research Institute, Infrastructure, Pavement Technology. University of Iceland.
    Viscoelastic Response Modelling of a Pavement under Moving Load2016In: Transportation Research Procedia, 2016, Vol. 14, p. 748-757Conference paper (Refereed)
    Abstract [en]

    This paper demonstrates the application of a generalized layered linear viscoelastic (LVE) analysis for estimating flexible pavements' structural response. The procedure is based on the Multi-Layered Elastic Theory (MLET) and the elastic-viscoelastic correspondence principle using a numerical inverse Laplace transform. A comparison of the direct layered viscoelastic responses with approximate solutions based on the elastic collocation method was also carried out. Furthermore, it is proposed to use the collocation method using LVE solutions at selected time durations in order to improve the accuracy of the elastic collocation method. The LVE collocation method was further extended for analysis of moving loads. The method was illustrated by analysing a pavement structure subjected to moving wheel loads of 30, 50, 60 and 80 kN using a Heavy Vehicle Simulator (HVS). The various responses (stresses and strains) in the pavement, at different pavement temperatures, were measured using various types of sensors installed in the structure. The LVE calculations agreed very well with the measurements.

  • 93.
    Ahmed, Abubeker W
    et al.
    Swedish National Road and Transport Research Institute, Infrastructure, Pavement Technology.
    Rahman, Mohammad Shafiqur
    Swedish National Road and Transport Research Institute, Infrastructure, Pavement Technology.
    Erlingsson, Sigurdur
    Swedish National Road and Transport Research Institute, Infrastructure, Pavement Technology.
    Impact of longer and heavier vehicles on the performance of asphalt pavements: A laboratory study2018In: Bearing Capacity of Roads, Railways and Airfields - Proceedings of the 10th International Conference on the Bearing Capacity of Roads, Railways and Airfields, BCRRA 2017, CRC Press/Balkema , 2018, p. 483-490Conference paper (Refereed)
    Abstract [en]

    Historically, Longer and Heavier Vehicles (LHVs) have been permitted to operate in Sweden. Since 1996 and as of the beginning of 2015, the maximum gross vehicle weight of 60 tons and a length of up to 25.25 m have been permitted. The Swedish Transport Administration has decided to further increase the maximum gross vehicle weight to 74 tons and studies are undergoing to evaluate the impact of the proposed LHVs on existing transport infrastructure. To this end, repeated load triaxial tests and indirect tensile fatigue tests were conducted on selected conventional asphalt mixtures to investigate and quantify the impact of single, tandem and tridem axle configurations on permanent deformation and fatigue performances of conventional asphalt pavements. In addition, fatigue tests for selected LHV scenarios were conducted. This paper presents the results of the laboratory tests and simulations conducted. The test results have clearly demonstrated the impact of the different axle configurations on the rutting and fatigue performances of the mixture. Furthermore, such results can explain the significance of axle configuration on modelling the rutting and fatigue performances of asphalt pavements.

  • 94.
    Ahmed, Abubeker W
    et al.
    Swedish National Road and Transport Research Institute, Infrastructure, Pavement Technology.
    Rahman, Mohammad Shafiqur
    Swedish National Road and Transport Research Institute, Infrastructure, Pavement Technology.
    Erlingsson, Sigurdur
    Swedish National Road and Transport Research Institute, Infrastructure, Pavement Technology.
    Impact of tire types and configurations on responses of a thin pavement structure2018In: Advances in Materials and Pavement Performance Prediction: Proceedings of the International AM3P Conference, 2018, London: CRC Press , 2018, p. 271-274Conference paper (Refereed)
    Abstract [en]

    The objective of this study was to assess the impact of tire and tire configurations on the responses of a thin asphalt pavement structure by means of full-scale tests using a Heavy Vehicle Simulator (HVS). A total of six different types of tires, four single and two dual tire configurations, were investigated. The structure was instrumented to measure tensile strains at the bottom of the asphalt layer and vertical stresses and strains in the unbound base, subbase and subgrade layers. The results indicated that, in general, single tire configurations produced higher tensile strain at the bottom of the asphalt layer and higher vertical stresses and strains in unbound base, subbase and subgrade layers.

  • 95.
    Ahmed, Abubeker W
    et al.
    Swedish National Road and Transport Research Institute, Infrastructure, Pavement Technology.
    Said, Safwat F.
    Swedish National Road and Transport Research Institute, Infrastructure, Pavement Technology.
    Lu, Xiaohu
    Nynäs AB.
    Carlsson, Håkan
    Swedish National Road and Transport Research Institute, Infrastructure, Measurement technology and engineering workshop.
    Pavement performance follow-up and evaluation of polymer-modified test sections2018In: The international journal of pavement engineering, ISSN 1029-8436, E-ISSN 1477-268X, p. 1-14Article in journal (Refereed)
    Abstract [en]

    Between 2003 and 2006, a test road consisting of several conventional and polymer-modified structures was built on a motorway. Different combinations of styrene–butadiene–styrene (SBS) and ethyl vinyl acetate (EVA) polymer-modified binders were used. The test structures have been in service since then and have been monitored for over 9 years. The resistance of the different types of asphalt concrete mixes to rutting and cracking was measured and predicted. The impact of ageing on the mixes was also evaluated. Although all the sections are in good condition after 9 years of traffic, the predicted differences between the test sections based on the PEDRO (Permanent Deformation of asphalt concrete layers for Roads) approach and laboratory evaluations are noticeable. Lateral wander and transverse profile measurements indicated that studded winter tyre wear contributed to most of the rutting compared to permanent deformation due to heavy traffic. The unmodified mixes exhibited considerable ageing and the SBS-modified mixes were least affected by ageing. Furthermore, the SBS-modified base mix produced significantly better fatigue resistance than the conventional base mix. However, further investigations of the relationships between bitumen and mix properties and further follow-ups of the test sections are recommended to validate the findings.

  • 96.
    Ahmed, Ishtiaque
    et al.
    Faculty of Civil Engineering, University Technology Malaysia (UTM), Malaysia.
    Ahmed, Bayes
    IMC Worldwide Limited, Baridhara, Dhaka, Bangladesh.
    Urban Road Accidents in Dhaka, Bangladesh2013In: Proceedings of the 16th International Conference Road Safety on Four Continents: Beijing, China. 15-17 May 2013, Linköping: Statens väg- och transportforskningsinstitut, 2013Conference paper (Other academic)
    Abstract [en]

    Dhaka, the capital city of Bangladesh, is the most vulnerable city both in terms of total number of accidents and accident rates. A total number of 2,720 accidents occurred during 2007-2011. This has caused a total of 1,481 numbers of pedestrian fatal accidents with 1,562 pedestrian fatal casualties. The primary objective of the paper is to study the characteristics of the road traffic accidents in Dhaka. The study area for this study is Dhaka Metropolitan Area. The paper focused on a few selected parameters a) Trend in overall accident rates b) Monthly variation of accident rates c) Accidents by severity levels d) Collision types e) Accidents in different lighting conditions. The raw data in the form of Accident Report Forms (ARFs) were collected from Dhaka Metropolitan Police (DMP). A GIS database was prepared for accidents showing locations and details for the period of 2007-2011. The analysis showed that on an average, the total number of traffic accidents is reduced by 11% each year. No profound effect of weather/season on road accidents is found. Fatal accidents and motor collisions are decreasing while injury accidents are increasing. Most traffic accidents: cause fatality (69%) and hit a pedestrian (60%). Fifty four percept of the accidents occurred during daytime. The paper recommends improvement measures for the road accident data collection and management system in Dhaka, Bangladesh. That includes the training need for the police staff, need for a geo-referenced database for data storage and management and involvement of multiple agencies in the process. This paper also recommends further studies on the extent and characteristics of underreporting of accidents.

  • 97. Ahrens, G-A
    et al.
    Becker, Klaus
    Traffic and the environment: Measures to reduce pollution caused by traffic1990Report (Other (popular science, discussion, etc.))
  • 98. Aigner-Breuss, Eva
    et al.
    Pilgerstorfer, Monika
    Anund, Anna
    Swedish National Road and Transport Research Institute, Traffic and road users, Human-vehicle-transport system interaction.
    Dukic, Tania
    Swedish National Road and Transport Research Institute, Traffic and road users, Human-vehicle-transport system interaction.
    Chalkia, Eleni
    Ferrarini, Chiara
    Montanari, Roberto
    Wacowska, Justyna
    Jankowska, Dagmara
    Diederichs, Frederik
    Pauzie, Annie
    Comparison and analysis of user and stakeholder needs across different countries2010Report (Other academic)
    Abstract [en]

    The current deliverable aims at presenting the results of the analysis of stakeholder needs, in order to have support for selecting the most relevant use cases. For the identification of user requirements of all stakeholders relevant to school transportation different methods were used:

    - Focus groups with representatives of one user or stakeholder group

    - Workshops with different stakeholders

    - 2 questionnaire surveys (Questionaire A: Road Experts, Questionaire B: children, parents and bus drivers)

    Problems and needs in the following areas were subject of discussions, interviews and questionnaires:

    - Behaviour of road users counteracting with school buses

    - Behaviour of pupils on the school bus and while entering and exiting the same

    - Design of bus stops

    - Protection of pupils on the school bus

    - Condition of school buses

    - Education of school bus drivers

    - Education of pupils concerning school transportation

    - Information flow

    - Route to/from school

    - Special needs of children with disabilities

    Results show that the organisation of school transport varies between countries and even within a country. Stakeholders underline the importance of consistent regulations and clear responsibilities as a basis for a safe way to school by bus.

  • 99.
    Ait Ali, Abderrahman
    et al.
    Swedish National Road and Transport Research Institute, Society, environment and transport, Transport economics.
    Eliasson, Jonas
    Linköpings universitet.
    Railway capacity allocation: a survey of market organizations, allocation processes and track access charges2019Report (Other academic)
    Abstract [en]

    In the last few decades, many railway markets (especially in Europe) have been restructured to allow competition between different operators. This survey studies how competition has been introduced and regulated in a number of different countries around the world. In particular, we focus on a central part of market regulation specific to railway markets, namely the capacity allocation process. Conflicting capacity requests from different train operators need to be regulated and resolved, and the efficiency and transparency of this process is crucial. Related to this issue is how access charges are constructed and applied. Several European countries have vertically separated their railway markets, separating infrastructure management from train services provisions, thus allowing several train operators to compete with different passengers and freight services. However, few countries have so far managed to create efficient and transparent processes for allocating capacity between competing train operators, and incumbent operators still have larger market-share in many markets.

  • 100.
    Ait Ali, Abderrahman
    et al.
    Swedish National Road and Transport Research Institute, Society, environment and transport, Transport economics.
    Warg, Jennifer
    KTH.
    Eliasson, Jonas
    Linköpings universitet.
    Pricing commercial train path requests based on societal costs2019Report (Other academic)
    Abstract [en]

    On deregulated railway markets, efficient capacity allocation is important. We study the case where commercial trains and publicly controlled traffic (“commuter trains”) use the same railway infrastructure and hence compete for capacity. We develop a method that can be used by an infrastructure manager trying to allocate capacity in a socially efficient way. The method calculates the loss of social benefits incurred by changing the commuter train timetable to accommodate a commercial train path request and based on this calculates a reservation price for the train path request. If the commercial operator’s willingness-to-pay for the train path exceeds the loss of social benefits, its request is approved. The calculation of social benefits takes into account changes in commuter train passengers’ travel times, waiting times, transfers and crowding, and changes in operating costs for the commuter train operator(s). The method is implemented in a microscopic simulation program, which makes it possible to test the robustness and feasibility of timetable alternatives. We show that the method is possible to apply in practice by demonstrating it in a case study from Stockholm, illustrating the magnitudes of the resulting commercial train path prices. We conclude that marginal societal costs of railway capacity in Stockholm are considerably higher than the current track access charges.

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