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  • 1.
    Albinsson, Anton
    et al.
    Chalmers Tekniska Högskola.
    Bruzelius, Fredrik
    Swedish National Road and Transport Research Institute, Traffic and road users, Driver and vehicle. Chalmers Tekniska Högskola.
    Hjort, Mattias
    Swedish National Road and Transport Research Institute, Traffic and road users, Driver and vehicle.
    Required friction utilization for friction estimation on wet asphalt, an experimental study2018In: The Dynamics of Vehicles on Roads and Tracks, CRC Press/Balkema , 2018, p. 407-412Conference paper (Refereed)
    Abstract [en]

    Real-time information about the friction coefficient between the tyre and the road can be used to improve active safety systems and is an enabler for autonomous vehicles. Large tyre force excitation is normally required to obtain an accurate friction estimate. This paper quantifies this requirement for four different tyre models on wet salted asphalt at water freezing temperatures. Cost functions and different tyre models are evaluated and the results are compared to a previous study performed for snow conditions. The suitability of commonly used tyre models for friction estimation on snow and wet asphalt has thus been investigated.

  • 2.
    Andersson, Jan
    et al.
    Swedish National Road and Transport Research Institute, Traffic and road users, Human-vehicle-transport system interaction.
    Renner, Linda
    Swedish National Road and Transport Research Institute, Traffic and road users, Human-vehicle-transport system interaction.
    Sandin, Jesper
    Swedish National Road and Transport Research Institute, Traffic and road users, Human-vehicle-transport system interaction. Swedish National Road and Transport Research Institute, Traffic and road users, Driver and vehicle.
    Fors, Carina
    Swedish National Road and Transport Research Institute, Traffic and road users, Vehicle technology and simulation. Swedish National Road and Transport Research Institute, Traffic and road users, Human Factors in the Transport System.
    Strand, Niklas
    Swedish National Road and Transport Research Institute, Traffic and road users, Vehicle technology and simulation. Swedish National Road and Transport Research Institute, Traffic and road users, Driver and vehicle.
    Hjort, Mattias
    Swedish National Road and Transport Research Institute, Traffic and road users, Human-vehicle-transport system interaction. Swedish National Road and Transport Research Institute, Traffic and road users, Driver and vehicle.
    Andersson Hultgren, Jonas
    Swedish National Road and Transport Research Institute.
    Almqvist, Sverker
    Swedish National Road and Transport Research Institute.
    Trafiksäkerhetspåverkan vid omkörning av 30-metersfordon2011Report (Other academic)
    Abstract [en]

    The Swedish Road Administration considers permitting longer and heavier trucks on Swedish roads, provided that they do not affect traffic safety. The purpose of the study was to investigate the effect of truck length, particularly accident risk associated with overtaking. Interviewed drivers of 30 meter trucks had not experienced the problems predicted by drivers of ordinary trucks concerning narrow roundabouts and intersections, but mentioned the importance of a supportive truck company, working environment and truck equipment. A simulator study investigated car drivers overtaking trucks 30 m and 18.75 m long on a 2+1 road where two lanes merges to one. The headway time gap was 0.2 sec. (sign.) shorter after overtaking the 30 meter truck in situations where the back was in the same relative position as of the 18.75 meter truck. A field study analysed video-recorded overtakings of a 30 meter and a 24 meter timber truck on a 2+1 road and a two-lane road. No significant differences were found between headway time gaps when overtaking the two trucks, regardless of road type. The latter result should be interpreted with great caution because of unevenly distributed data collected during specific conditions. The conclusions are that longer trucks may have a small negative effect on overtaking situations, and that further field studies are required.

  • 3.
    Andersson, Jan
    et al.
    Swedish National Road and Transport Research Institute, Traffic and road users, Human-vehicle-transport system interaction.
    Sandin, Jesper
    Swedish National Road and Transport Research Institute, Traffic and road users, Human-vehicle-transport system interaction.
    Renner, Linda
    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.
    Strand, Niklas
    Swedish National Road and Transport Research Institute, Traffic and road users, Human-vehicle-transport system interaction.
    Hjort, Mattias
    Swedish National Road and Transport Research Institute, Traffic and road users, Vehicle technology and simulation.
    Hultgren, J
    Almqvist, S
    Traffic safety effects when overtaking 30 meter trucks2012In: Advances in Human Factors and Ergonomics 2012- 14 Volume Set: Proceedings of the 4th AHFE Conference 21-25 July 2012 / [ed] Gavriel Salvendy, Waldemar Karwowski, Taylor & Francis, 2012Conference paper (Refereed)
    Abstract [en]

    The purpose of this paper is to investigate if the introduction of extra-long and heavy trucks has an effect on traffic safety on Swedish roads, especially in relation to overtaking maneuvers. Traffic safety effects will be measured in terms of road user behavior concerning accelerations and time slots. First, focus group interviews with heavy truck drivers. Truck drivers that do not drive extra-long trucks believe that the introduction of extra-long trucks will create a number of traffic safety problems especially in terms of conflicts with ordinary road users. The drivers of extra-long trucks do not experience the problems that ordinary truck drivers predict. The problems they experience can be taken care of with more planning (thinking ahead). They also believe that the traffic sign on the back of the extra-long vehicle has a positive effect. The truck company, working environment and truck equipment are other important aspects mentioned by the drivers of the extra-long vehicles.

    The simulator study investigates overtaking situations on a 2+1-lane highway, with extra-long trucks (30.4 m) and ordinary trucks (18.75 m). The results reveal that the distance from the rear/front of the truck to the point where only one lane exists affects car drivers’ decision to overtake, independently of truck length. If the truck is in the relatively same position, the timeslot for a safe overtaking maneuver before next one-lane section was reduced significantly for extra-long trucks compared to ordinary trucks. The conclusion is that there exist small tendencies which point in the direction of enhanced traffic safety problems with the introduction of extra-long trucks. The results should, however, be interpreted with caution as the number of data points was few and collected in specific situations and in specific conditions. It was neither considered how the introduction of longer and heavier trucks, given a constant amount of goods, reduces the number of heavy trucks on the road network.

  • 4.
    Bolling, Anne
    et al.
    Swedish National Road and Transport Research Institute, Traffic and road users, Vehicle technology and simulation.
    Jansson, Jonas
    Swedish National Road and Transport Research Institute, Traffic and road users, Vehicle technology and simulation.
    Genell, Anders
    Swedish National Road and Transport Research Institute, Traffic and road users, Vehicle technology and simulation. Swedish National Road and Transport Research Institute, Society, environment and transport, Environment.
    Hjort, Mattias
    Swedish National Road and Transport Research Institute, Traffic and road users, Vehicle technology and simulation.
    Lidström, Mats
    Swedish National Road and Transport Research Institute, Traffic and road users, Vehicle technology and simulation.
    Nordmark, Staffan
    Swedish National Road and Transport Research Institute, Traffic and road users, Vehicle technology and simulation.
    Palmqvist, Göran
    Swedish National Road and Transport Research Institute, Traffic and road users, Vehicle technology and simulation.
    Sehammar, Håkan
    Swedish National Road and Transport Research Institute, Traffic and road users, Vehicle technology and simulation.
    Sjögren, Leif
    Swedish National Road and Transport Research Institute, Infrastructure, Infrastructure maintenance.
    Ögren, Mikael
    Swedish National Road and Transport Research Institute, Society, environment and transport, Environment.
    SHAKE - an approach for realistic simulation of rough roads in a moving base driving simulator2010In: Trends in driving simulation design and experiments: proceedings of the driving simulation conference Europe 2010, Arcueil: Institut national de recherche sur les transports et leur securite, INRETS , 2010, p. 135-143Conference paper (Refereed)
    Abstract [en]

    With today’s advanced measurement equipment for measuring roads, it is possible to measure road geometry at high precision within a large span of wavelengths. Detailed information about the roads longitudinal and lateral profile, including macro texture, would in theory be sufficient for a realistic reproduction of road induced vibration and noise in a driving simulator. Especially, it would be possible to create a direct connection between the visual information of the road condition and the ride experience, which would increase the level of realism in the simulation. VTI has during three years performed an internal project called SHAKE with the aim to develop and implement models in VTI driving simulator III that use measured road data for generating realistic vibrations and audible road noise connected to the visual impression presented on the projection screen. This has indeed resulted in an more realistic driving experience, and a validation study with test persons driving both in the simulator and in the field has been undertaken. The OpenDRIVE standard is used as a framework for describing the road properties (e.g. visual, vibrations and noise). For this purpose some augumentations to the OpenDRIVE standard had to be made. This paper describes the technical implementations in the driving simulator, along with results from test drives on the implemented road sections

  • 5.
    Bolling, Anne
    et al.
    Swedish National Road and Transport Research Institute, Traffic and road users, Vehicle technology and simulation.
    Lidström, Mats
    Swedish National Road and Transport Research Institute, Traffic and road users, Vehicle technology and simulation.
    Hjort, Mattias
    Swedish National Road and Transport Research Institute, Traffic and road users, Vehicle technology and simulation.
    Nordmark, Staffan
    Swedish National Road and Transport Research Institute, Traffic and road users, Vehicle technology and simulation.
    Sehammar, Håkan
    Swedish National Road and Transport Research Institute, Traffic and road users, Vehicle technology and simulation.
    Sjögren, Leif
    Swedish National Road and Transport Research Institute, Infrastructure, Infrastructure maintenance.
    Genell, Anders
    Swedish National Road and Transport Research Institute, Society, environment and transport, Environment.
    Sörensen, Gunilla
    Swedish National Road and Transport Research Institute, Traffic and road users, Traffic safety, society and road-user.
    Improving the realism in the VTI driving simulators: Shake final report2012Report (Other academic)
    Abstract [en]

    The Swedish Road and Transport Research Institute (VTI) has three advanced moving base driving simulators. The aim of this project was to develop and implement new models concerning vibration, noise and graphics in order to improve the realism in the simulators. Moreover, a validation study was to be conducted.

    Within the frame of the project the following were achieved:

    • improvement of the tyre/road vibration models,
    • •improvement of the motion system by changing the rotation centre,
    • •improvement of the noise module facilitating reproduction of noise from tyre/road,
    • •synchronization of the impressions from graphics, noise and vibrations caused by the road surface.

    The validity of the models was tested in the VTI Simulator III. Statistical testing of differences between the car and the simulator indicated absolute validity for the subjective ratings of evenness and noise level and the objective measure speed, with the exception of areas surrounding speed limit signs where only relative validity was found. Relative validity was also indicated for the variable overall comfort. The results from the different validations show that the improvements have been successful and the driver in the simulator can now see, hear and feel the sensation of any road surface irregularities exactly when the wheels hit that part of the road. However, several improvements in the simulator models can still be desired.

  • 6.
    Bruzelius, Fredrik
    et al.
    Swedish National Road and Transport Research Institute, Traffic and road users, Vehicle technology and simulation.
    Hjort, Mattias
    Swedish National Road and Transport Research Institute, Traffic and road users, Vehicle technology and simulation.
    Andersson, Håkan
    Swedish National Road and Transport Research Institute, Infrastructure, Crash safety.
    Towards an Indoor Winter Tire Classification Test2012In: Proceedings of VSDIA 2012, 2012Conference paper (Refereed)
    Abstract [en]

    From a traffic safety perspective it is highly motivated to define winter tires interms of their performance in icy road conditions. The present definition of winter(snow) tires, introduced in the EU in 2012, is based on packed snow performance.The present paper investigates the feasibility of an indoor winter tire classificationtest on ice. Results presented here indicates that a test procedure in an indoorhockey rink is possible, with relatively high repeatability. However, further fieldtest is required to fully establish feasibility of the procedure.

  • 7.
    Bruzelius, Fredrik
    et al.
    Swedish National Road and Transport Research Institute, Traffic and road users, Vehicle technology and simulation.
    Hjort, Mattias
    Swedish National Road and Transport Research Institute, Traffic and road users, Vehicle technology and simulation.
    Svendenius, Jacob
    BorgWarner TTS.
    Validation of a basic combined slip tyre model for use in friction estimation applications2014In: Proceedings of the Institution of mechanical engineers. Part D, journal of automobile engineering, ISSN 0954-4070, E-ISSN 2041-2991, Vol. 228, no 13, p. 1622-1629Article in journal (Refereed)
    Abstract [en]

    Tyre modelling is an important part of understanding and estimating the tyre-road friction. In this paper a basic steady-state tyre model for the combined-slip case is derived. The model is intended to be used in friction estimations applications, where the model complexity is of high priority. The model, described using only two parameters, is validated with measured data from various conditions and tyre types using mobile measurement equipment. The performance from the measurements suggests that only two parameters are sufficient for the combined-slip case.

  • 8.
    Eriksson, Louise
    et al.
    Swedish National Road and Transport Research Institute, Society, environment and transport, Mobility, actors and planning processes.
    Nerhagen, Lena
    Swedish National Road and Transport Research Institute, Society, environment and transport, Transport economics Borlänge.
    Bolling, Anne
    Swedish National Road and Transport Research Institute, Traffic and road users, Vehicle technology and simulation.
    Jansson, Jonas
    Swedish National Road and Transport Research Institute, Traffic and road users.
    Hjort, Mattias
    Swedish National Road and Transport Research Institute, Traffic and road users, Vehicle technology and simulation.
    Nilsson, Lena
    Swedish National Road and Transport Research Institute, Traffic and road users.
    Gustafsson, Mats
    Swedish National Road and Transport Research Institute, Society, environment and transport, Environment.
    Blomqvist, Göran
    Swedish National Road and Transport Research Institute, Society, environment and transport, Environment.
    Karlsson, Bo O
    Swedish National Road and Transport Research Institute, Society, environment and transport, Enviroment and traffic analysis.
    Tema miljörisker: miljörisker och trafikanters beteenden2011Report (Other academic)
    Abstract [en]

    This report compiles the results from the project Theme Environmental risks. More specifically, the project concerned how different transport related environmental risks influence different road users and how their behaviour influence the environment. The project aimed at preparing for interdisciplinary research about environmental risks at VTI. The project was divided into three parts. The first subproject aimed at compiling literature about transport related environmental risks from psychological and economic perspectives, and in the second subproject a willingness to pay study was outlined where both economic and psychological principles were considered. In the third subproject, a simulator study was outlined. The focus was to study environmental effects of driving under controlled circumstances in the driving simulator. The report is divided into two parts. In part 1, the results from the literature review and the proposal for a willingness to pay study are described (subproject 1 and 2). This part is written in English. Part 2 contains a project outline for a simulator study in the form of an research project application (project 3). This part is written in Swedish.

  • 9.
    Gustafsson, Mats
    et al.
    Swedish National Road and Transport Research Institute.
    Berglund, Carl Magnus
    Swedish National Road and Transport Research Institute.
    Forsberg, Bertil
    Swedish National Road and Transport Research Institute.
    Forsberg, Inger
    Swedish National Road and Transport Research Institute.
    Forward, Sonja
    Swedish National Road and Transport Research Institute.
    Grudemo, Stefan
    Swedish National Road and Transport Research Institute.
    Hammarström, Ulf
    Swedish National Road and Transport Research Institute.
    Hjort, Mattias
    Swedish National Road and Transport Research Institute.
    Jacobson, Torbjörn
    Swedish National Road and Transport Research Institute.
    Johansson, Christer
    Ljungman, Anders
    Nordström, Olle
    Swedish National Road and Transport Research Institute.
    Sandberg, Ulf
    Swedish National Road and Transport Research Institute.
    Wiklund, Mats
    Swedish National Road and Transport Research Institute.
    Öberg, Gudrun
    Swedish National Road and Transport Research Institute.
    Effekter av vinterdäck: en kunskapsöversikt2006Report (Other academic)
    Abstract [en]

    Choice of winter tyres has, from mainly being a matter of safety and economic costs for wearing of road pavements, during later years also become a matter of inhalable particles formed during pavement wear from studded tyres and their negative effects on public health. Further, the tyres' effects on environment and noise have been illustrated in several studies. The issue is also complicated by the fact that tyre choice effects on traffic safety have several components, including such diverging parameters as friction and behaviour. Finally all aspects have to be evaluated from a socioeconomic point of view for society to be able to decide which kind of distribution of tyre types that is the most profitable. This report is a summary of current knowledge in this complex research field.

  • 10.
    Gustafsson, Mats
    et al.
    Swedish National Road and Transport Research Institute.
    Blomqvist, Göran
    Swedish National Road and Transport Research Institute.
    Brorström-Lunden, Eva
    Dahl, Andreas
    Gudmundsson, Anders
    Hjort, Mattias
    Swedish National Road and Transport Research Institute.
    Johansson, Christer
    Jonsson, Per
    Swedish National Road and Transport Research Institute.
    Swietlicki, Erik
    NanoWear: nanopartiklar från slitage av däck och vägbana2009Report (Other academic)
    Abstract [en]

    Particles from road and tire wear have in recent years come to the fore as an important and relatively unexplored contribution to air particulate pollution. Mechanically generated wear particles are relatively coarse (>0.5 microns), but in controlled trials in VTI's road simulator it has been found that an ultra-fine fraction (< 100 nm) of particles is formed from tyre and pavement wear. This project was initiated to identify the source of these nanoparticles. The results show that the nanoparticles of the size 30-50 nm occur only from tests with studded tyres. One of the two tested Nordic unstudded winter tyres produced an even finer particle fraction (<10 nm), while the other unstudded winter tyre type did not give rise to nanoparticles. Tests with summer tyres did not result in the formation of nanoparticles. It is clear that the fine particle fraction contains higher relative concentrations of sulphur, which is present at relatively high levels in both bitumen and tyres. It is unclear whether the ultrafine particles formed from studded tyre wear of road pavement in the road simulator also occur in real traffic. If so, this may affect the assessment of health effects from different traffic related particle sources.

  • 11.
    Hjort, Mattias
    Swedish National Road and Transport Research Institute, Traffic and road users, Vehicle technology and simulation.
    Measuring tyre performance in ESC intervention situations2013In: Proceedings of the international conference Science meets Tires: Perspectives for Tire Technology. Aachen, 11-12 September 2013., 2013Conference paper (Other academic)
    Abstract [en]

    Fatal accidents during winter time in Sweden are to a large extent due to vehicle spinning. Therefore, it is crucial to analyse and compare vehicle/tyre performance on slippery roads with respect to oversteering. We have performed experimental tests to compare the stability performance of various winter tyres on ice, with and without an electronic stability system (ESC). Two different test methods are presented, one closed loop and one open loop test. Results from both studies are discussed, and it is clear that different tyres may have a large impact on vehicle stability even with ESC activated

  • 12.
    Hjort, Mattias
    Swedish National Road and Transport Research Institute, Traffic and road users, Driver and vehicle.
    Mönsterdjupets inverkan på väggrepp på is för släpvagnsdäck till tunga fordon: jämförande tester2019Report (Other academic)
    Abstract [en]

    In Sweden the current regulation for minimum tread depth for heavy vehicles in the winter period is different for trailer axles compared to drive or steer axles. While the requirement for the latter axles are 5 mm tread depth, on trailer axles 1,6 mm is required.

    The purpose of this study has been to investigate whether there is reason to increase the tread depth requirement for heavy vehicle trailer tyres during the winter period in Sweden, and if so, suggest a new tread depth limit. The study was limited to ice conditions, and ice grip for a number of different trailer tyres with different tread depth was measured on smooth ice in VTI’s tyre test facility.

    Before conducting the test there was no clear hypothesis for how the ice grip would be affected by a lower tread depth. An increase of the grip, as well as a decrease, were both possible outcomes for a diminished tread depth.

    Four different tire models in a dimension common for heavy vehicle trailer tyres (385/55-R22.5) were chosen for the tests. Every model was tested in a new state, as well as with 5, 3, and 1.6 mm tread depth. It was decided to use naturally worn tyres which meant that in total 16 different tyres were used in the study. The difficult task of finding identical tyre models and dimensions with specified tread depth forced us to also include some tyres with the larger profile (285/65-R22.5). This is however not considered to affect the results of the test. All the tyres were winter tyres, and most of them were also marked with the 3PMSF symbol, which means that they have passed a standardized grip test on snow.

    Both brake and steer test were conducted. Five different grip related attributes were investigated: peak friction at braking, friction at locked wheel braking, cornering stiffness, cornering peak friction, and cornering friction with large slip angle

  • 13.
    Hjort, Mattias
    Swedish National Road and Transport Research Institute.
    SUV-däcks väggrepp på is2006Report (Other academic)
    Abstract [sv]

    En däcktyp som ökar i användning år från år är de av så kallad SUV-typ (Sport Utility Vehicles). Var 17:e nybil som såldes i Sverige under 2004 var en SUV. SUV-däck har större dimensioner och utsätts för större hjullaster jämfört med vanliga personbilsdäck. Dessutom finns det bland SUV-däcken en större variation i modellutbudet (allt från rena terrängdäck till lågprofildäck) jämfört med personbilsdäcken, vilket innebär att risken att välja ett vinterdäck med sämre köregenskaper ökar. VTI har därför undersökt isfriktionen hos 23 olika M+S-märkta däck samt ett sommardäck av den dimension som är standard på Volvo XC90. Av M+S-däcken var 7 st. dubbdäck, 10 st. odubbade vinterdäck samt 6 st. icke godkända vinterdäck av terräng- eller allseasontyp, dvs. ej särskilt framtagna för vinterkörning. Testerna utfördes i VTI:s stationära däckprovningsanläggning på is med temperaturen -3°C. Då vi enbart utfört isfriktionstester kan vi inte uttala oss om dessa däcks egenskaper på barmark. Resultaten av våra tester visar att - SUV-däck som är märkta M+S men inte godkända som vinterdäck är generellt sämre på slät is jämfört med SUV-däck som är vinterdäcksgodkända - Speciellt är broms- och styrstabiliteten dålig på is för SUV-däck som inte är godkända som vinterdäck, vilket är allvarligt, och i värsta fall kan leda till att antisladdsystemet i praktiken blir verkningslöst om man vrider för mycket på ratten i en nödsituation - Odubbade vinterdäck (friktionsdäck) för SUV:ar är generellt hårdare än friktionsdäck för personbilar, vilket normalt innebär ett sämre is- och snögrepp - Dubbade SUV-däck har betydligt bättre isgrepp än friktionsdäck, terrängdäck och allseasondäck.

  • 14.
    Hjort, Mattias
    Swedish National Road and Transport Research Institute, Traffic and road users, Vehicle technology and simulation.
    The Snow Grip of Heavy Vehicle Drive Axle Winter Tyres2012In: Proceeding at the International Symposium on Heavy Vehicle Transport Technology, 2012Conference paper (Refereed)
    Abstract [en]

    Every winter in Sweden, winter roadways pose problems for heavy vehicles. Steep gradients can be difficult to pass when it is slippery, which has implications also for other traffic when congestion occurs. To reduce the problems it has been discussed whether to impose a legal requirement for winter tyres on drive axle for trucks. This papers presents test results of the available snow grip from test track measurements comparing different drive axle tyres. A summer tyre, together with three winter tyres, of which one was retreaded, were selected for tests. The results of the traction tests show that there can be a big difference in grip between winter and summer tyres on packed snow. The difference between the tyres, however, is strongly dependent on the nature of the snow surface, so it is difficult to give general values. Theoretical calculations show that a vehicle’s rolling resistance can have a major impact on a vehicles climbing ability. With a high rolling resistance, which may be the result of loose snow on the road, the difference between good and bad grip on the drive tyres becomes even more significant.

  • 15.
    Hjort, Mattias
    Swedish National Road and Transport Research Institute, Traffic and road users, Vehicle technology and simulation.
    Vinterdäck på drivaxel till tunga fordon: en väggreppsstudie2012Report (Other academic)
    Abstract [sv]

    Det saknas vetenskapligt utförda studier angående hur stora skillnader i väggrepp som kan förväntas mellan vinter- och sommardäck på olika vinterväglag för kategorin tunga fordons drivaxeldäck. Då resurserna var begränsade fanns det endast möjlighet att testa ett fåtal däck. Ett sommardäck tillsammans med tre olika vinterdäck, varav ett regummerat, valdes ut för testerna. Vidare utfördes testerna på en testbana med en typ av vinterväg: packad snö.

    Grepptesterna på packad snö visar att det kan vara stor skillnad i grepp mellan vinter- och sommardäck. Skillnaden mellan däcken är dock starkt beroende av snöytans beskaffenhet, varför det är vanskligt att ange generella värden. Minst skillnad mellan däcken uppmättes på riktigt hård packad snö, där vinterdäcket presterade 20 % bättre grepp än sommardäcken. Då snöytan var något mjukare och med snöfall till och från presterade vinterdäcket drygt 60 % bättre grepp än sommardäcket, vilket skulle innebära att flera fordonskombinationer skulle klara dubbelt så branta backar med det specifika snöväglaget med vinterdäck på drivaxeln jämfört med sommardäck. De båda testade snöytorna var dock båda relativt hårda och erbjöd bra grepp för alla testade däck. Vi kan inte från dessa tester förutsäga hur stora skillnader mellan däcktyperna som skulle erhållits vid tester på halare snöunderlag. Teoretiska beräkningar visar att fordonets rullmotstånd kan ha stor påverkan på hur väl ett fordon kan ta sig upp för en backe. Tjock lössnö på vägen kan därför kraftigt reducera ett fordons backtagningsförmåga. Vid stort rullmotstånd blir skillnaden mellan bra och dåligt grepp på drivdäcken ännu större.

  • 16.
    Hjort, Mattias
    Swedish National Road and Transport Research Institute, Traffic and road users, Driver and vehicle.
    Vinterdäck till cykel: ett jämförande test2018Report (Other academic)
    Abstract [en]

    The purpose of this study has been to compare the winter road grip of various bicycle tyres, as well as a pair of unstudded winter tyres, through cycling tests. In addition to grip, other characteristics that could be important to a cyclist, such as rolling resistance and wear resistance, were also tested.

    The tyre’s grip on ice was tested by brake tests and manoeuvring tests indoors in an ice hockey rink. Four different test drivers were used to capture differences in driver behaviour, as well as to get a variation in the cyclist’s weight. The tyre rolling resistance was measured by indoor coast-down tests. Finally, the grip was tested on dry and wet asphalt by outdoor brake tests. Between the various tests, the studded tyres were examined with regard to the number of lost studs. In total, seven different studded tyres, two unstudded winter tyres and a summer tyre were tested.

    The brake tests on dry and wet asphalt could not show any difference in performance between the different tyres. The winter tyres, studded as well as unstudded, had as good grip on asphalt as the tested summer tyre. In the case of ice grip, the two tyres with the highest number of studs, 240, were clearly superior to the others.

    The rolling resistance tests showed differences between the different tyres and it is not the number of studs but rather the rubber properties and the puncture protection that has the greatest impact on the rolling resistance. The wear tests indicated that some of the tested models may be particularly prone to losing studs, but as the tests included only two samples of each tyre model, it is not possible to draw certain conclusions regarding wear resistance.

  • 17.
    Hjort, Mattias
    et al.
    Swedish National Road and Transport Research Institute, Traffic and road users, Vehicle technology and simulation.
    Andersson, Håkan
    Swedish National Road and Transport Research Institute, Infrastructure, Crash safety.
    Säkerhetsrisker kopplat till däck, fälg och hjul: en litteraturstudie2012Report (Other academic)
    Abstract [en]

    A literature review about the road safety effects associated with tires, rims and wheels was carried out, where the literature search was done in consultation with the VTI Library and information centre. The outcome resulted in approximately 90 different references, most of which refer to research articles in peer reviewed journals, but also some independent reports and books. A clear distinction was made with slip-related accidents related to winter conditions and different types of snow tires/tire characteristics not included in the study. Furthermore, only the type of accidents that occurs during vehicle operation was treated, which means that work accidents occurring during a service are not included in the study.

    There is not much research published on the rim effect on road safety, and a U.S. accident investigator believes that the wheels generally are extremely reliable. Of the anomalies that can occur for the wheel as a whole, loosening of the wheel is the most serious. The studies that we found dealing with wheel imbalance only apply to comfort problems and increased road wear. Different wheel alignment will affect a vehicle's handling, but we have not found any study that has related this to road safety. For tires, we found no research on how different tire sizes and brands mounted on a vehicle affect its safety. Several studies show that there is a risk involved with mounting new tires on the front axle and worn tires on the rear axle. There is a consensus that during the replacement of two tires, the new tires should always be positioned on the rear axle, regardless if the vehicle is front or rear wheel driven. A number of studies show how the tread depth affects the wet grip during braking, and how the tires with less than 3 mm tread depth lose about half of the available friction compared to new tires.

  • 18.
    Hjort, Mattias
    et al.
    Swedish National Road and Transport Research Institute, Traffic and road users, Vehicle technology and simulation.
    Andersson, Håkan
    Swedish National Road and Transport Research Institute.
    Jansson, Jonas
    Swedish National Road and Transport Research Institute, Traffic and road users.
    Mårdh, Selina
    Swedish National Road and Transport Research Institute, Traffic and road users, Human-vehicle-transport system interaction.
    Sundström, Jerker
    Swedish National Road and Transport Research Institute.
    A test method for evaluating safety aspects of ESC equipped passenger cars: a prototype proposal2009Report (Other academic)
    Abstract [en]

    Active safety systems are becoming increasingly common in today's vehicles. Electronic Stability Control (ESC) systems were introduced during the end of the 1990s, and accident statistics show that they have had a huge impact on traffic safety. In the USA, a new legislation has recently been adopted which demands on every new light vehicle that is sold to be equipped with ESC, beginning 2011. New systems require new testing methods, and there is a need expressed by the New Car Assessment Program (NCAP), which at present time only evaluates the passive safety of cars, also to include tests for active safety systems. In a previous VTI work, a literature review regarding methods for the evaluation of traffic safety effects of Antilock Braking Systems (ABS) and ESC was performed. Based on the findings of that review, we have proceeded with defining a test method for evaluating safety aspects of ESC equipped passenger cars. The objective has been to suggest a (prototype) test method that can be used for a more holistic evaluation of the safety effect of ESC in cars, including the driver behaviour perspective. From discussions with leading experts on traffic safety and ESC, possible benefits of ESC systems on traffic safety were identified. In addition to increasing the yaw stability of the vehicle, the following ESC benefit effects were identified: - A warning system for slippery roads. ESC activation indication may act as a warning system to the driver about slippery road conditions. - Reduced collision speed. In a critical situation, ESC activation may reduce the collision speed, which will mitigate the outcome of the collision. - Improved vehicle roll stability. The ESC system may also stabilise the vehicle with respect to untripped rollovers. Most rollovers are however tripped rollovers, which can occur when a vehicle, with some lateral slip, strikes an object or slides off the road. These rollovers also benefit from the ESC system as it aids in keeping the vehicle on the road.

  • 19.
    Hjort, Mattias
    et al.
    Swedish National Road and Transport Research Institute, Traffic and road users, Vehicle technology and simulation.
    Bruzelius, Fredrik
    Swedish National Road and Transport Research Institute, Traffic and road users, Vehicle technology and simulation.
    Andersson, Håkan
    Swedish National Road and Transport Research Institute, Infrastructure, Crash safety.
    The importance of tyre grip for the ESC function on icy roads2011Conference paper (Refereed)
    Abstract [en]

    In this study we have investigated how tyres with different road grip affect the stability of passenger cars equipped with Electronic Stability Control (ESC) systems during winter road conditions. A field test with a double lane change manoeuvre on ice was performed using 6 test drivers, 4 different passenger cars and 4 different studless winter tyres. The specific tyres were chosen to represent a large difference of road grip on ice and snow. The results show that there was a large performance difference between the best and worst tyres with ESC off, and that activating ESC only resulted in a minor increase of performance.

  • 20.
    Hjort, Mattias
    et al.
    Swedish National Road and Transport Research Institute, Traffic and road users, Vehicle technology and simulation.
    Bruzelius, Fredrik
    Swedish National Road and Transport Research Institute, Traffic and road users, Vehicle technology and simulation.
    Andersson, Håkan
    Swedish National Road and Transport Research Institute, Infrastructure, Crash safety.
    Överstyrning på is och snö med olika vinterdäck: metodutveckling och fältstudie2011Report (Other academic)
    Abstract [en]

    Traffic accidents during winter time are to a larger extent categorized by loss of vehicle control resulting in a skidding accident, compared to accidents occurring summer time. In a study by the Swedish Transport Administration, it was shown that for fatal accidents happening winter time, skidding had occurred in 64 per cent of the accidents on winter road conditions. Out of these, 82 per cent were so called over steering accidents, i.e. events where the vehicle starts to spin.

    The purpose of this study was to develop av method for testing a vehicle's stability during oversteering on slippery roadways, and to use this method to test how large the difference is between different kinds of winter tyres on ice and snow.

    A test method based on NTHSA's sine-with-dwell manoueuvre was developed. The manouevre uses a steering robot and induces heavy oversteering on slippery surfaces, such as ice and snow.

    The manouevre was then used with an ESC equipped rear-wheel driven passenger car, fitted with both new and worn winter tyres of the three different kinds that are available in Sweden, to compare the level of oversteering that is possible to obtain with a steering manouevre on different ice and snow surfaces. The results show that studded tyres are more stable than unstudded on smooth ice. Even the worn studded tyre, with only a fraction of the studs remaining, is performing well compared to the unstudded tyres, and is comparable to a new unstudded winter tyre of Nordic type and much better than the tyres of Central European type. The winter tyres of Central European type stand out as those generating most oversteering on this surface. On surfaces with higher friction level, the tyres with least grip are also those that generate least oversteering, which makes it difficult to discuss these results in terms of traffic safety.

  • 21.
    Hjort, Mattias
    et al.
    Swedish National Road and Transport Research Institute, Traffic and road users, Vehicle technology and simulation.
    Bruzelius, Fredrik
    Swedish National Road and Transport Research Institute, Traffic and road users, Vehicle technology and simulation.
    Andersson, Håkan
    Swedish National Road and Transport Research Institute, Infrastructure, Crash safety.
    Kharrazi, Sogol
    Swedish National Road and Transport Research Institute, Traffic and road users, Vehicle technology and simulation.
    Towards a method for determining maximum oversteer in slippery conditions2013In: Proceedings of 23rd International Symposium on Dynamics of Vehicles on Roads and Tracks (IAVSD'13). Qingdao, China, 19-23 August, 2013., 2013Conference paper (Refereed)
    Abstract [en]

    Fatal accidents during winter time in Sweden are to a large extent due to vehicle spinning. Therefore, it is crucial to analyse and compare vehicle/tyre performance on slippery roads with respect to oversteering. In this study, a new test method for evaluation of vehicle's stability during oversteering on icy roadways is developed and evaluated using a series of tests with a rear wheel driven car, equipped with ESC, and six different tyres on ice test tracks in northern Sweden. The test method consists of an asymmetric sine-with-dwell manoeuvre and a measure forquantifying the level of oversteering based on the relation between yaw rate and lateral acceleration. The test results show good robustness of the method, and that it can successfully rate the various tyres performance on polished ice. However, to have a fair comparison, the proposed method should be modified to take into account the steering ability of the tyres and the consequent difference in the manoeuvre severity when tested with tyres with different side grip.

  • 22.
    Hjort, Mattias
    et al.
    Swedish National Road and Transport Research Institute, Traffic and road users, Vehicle technology and simulation.
    Bruzelius, Fredrik
    Swedish National Road and Transport Research Institute, Traffic and road users, Vehicle technology and simulation.
    Andersson, Håkan
    Swedish National Road and Transport Research Institute, Infrastructure, Crash safety.
    Krafft, Maria
    Folksam.
    Ydenius, Anders
    Folksam.
    Rizzi, Matteo
    Vectura.
    Jämförelse av vinter och sommardäck på barmark sommartid: tester, riskanalys och djupstudier2015Report (Other academic)
    Abstract [en]

    In Sweden non-studded winter tyres has become increasingly popular during the winter season. Since it is allowed to use non-studded winter tyres also during summer time, a large number of drivers choose to do that. The purpose of this study has been to investigate the difference in road grip between winter- and summer tyres summer time, and to assess possible effects on traffic safety. A field test was carried out where road grip was measured on dry and wet asphalt pavement with different types of tyres. The results showed that the winter tyres (non-studded of Nordic type) led to 15–20 per cent longer braking distances compared to summer tyres. Accident risk analyses were performed for three types of accidents: rear end collision, frontal collision and collision with pedestrian. The study indicated that using winter tyres leads to an increase in accident risk for all three accident types. At low collision speeds the absolute increase in risk is small, maybe just a few percent, but the relative increase may be large, sometimes up to 100 per cent. In-depth studies of fatal accidents indicated a 3 per cent increase of risk from using winter tyres summertime, compared to summer tyres. However, this result was not statistically significant.

  • 23.
    Hjort, Mattias
    et al.
    Swedish National Road and Transport Research Institute, Traffic and road users, Vehicle technology and simulation.
    Eriksson, Olle
    Swedish National Road and Transport Research Institute, Infrastructure, Infrastructure maintenance.
    Test av is- och snögrepp för slitna vinterdäck: jämförelse av olika kategorier av vinterdäck2015Report (Other academic)
    Abstract [en]

    This study has measured ice and snow grip for used and new winter tyres, with the purpose to investigate how the road grip on ice and snow for different types of winter tyres degrade by age and degree of wear. In total, 77 tyres have been tested, of which 27 were completely new while 50 were used. The tyres have been tested on smooth ice and packed snow. The results show that with respect to ice grip, the studded tyres have a larger performance decrease when worn, than the unstudded winter tyres. However, the ice grip of worn studded tyres were still clearly superior to that of worn unstudded tyres. The used unstudded tyres of European type have in general a very poor ice grip, on level with two summer tyres that were also tested. On snow, the unstudded winter tyres of Nordic type in general have a slightly better grip than the studded tyres, while the unstudded tyres of European type performs worse. The snow grip for the used tyres is significantly worse than used tyres of the other two types. The study also shows that the premium tyres in general have better ice and snow performance compared to the budget tyres, for both new and used tyres.

  • 24.
    Hjort, Mattias
    et al.
    Swedish National Road and Transport Research Institute, Traffic and road users, Driving Simulation and Visualization.
    Eriksson, Olle
    Swedish National Road and Transport Research Institute, Infrastructure, Infrastructure maintenance.
    Väggrepp på våt asfalt för slitna och nya vinterdäck: jämförelse av olika kategorier av vinterdäck2016Report (Other academic)
    Abstract [sv]

    Denna studie har mätt väggrepp på våt, saltad asfaltväg vid temperaturer kring noll grader för slitna och nya vinterdäck i syfte att undersöka hur väggreppet för de tre olika förekommande typerna av vinterdäck i Sverige försämras med ålder och slitage. Även sommardäck har ingått i studien. Totalt har 84 däck testats, varav 31 helt nya däck och 53 begagnade. Resultaten visar att dubbdäck och nordiska odubbade vinterdäck presterar likvärdigt på detta underlag. Skillnaden mellan nya och slitna däck av dessa två typer är för de flesta undersökta prestandamått i praktiken obefintlig. De nya europeiska däcken presterar cirka 10–13 procent bättre än nya dubbdäck och nordiska odubbade vinterdäck på den våta asfalten vid det aktuella väderförhållandet. För de slitna däcken är prestandaövertaget för de europeiska däcken mindre, cirka 5–7 procent bättre än de andra två typerna av vinterdäck. Sommardäcken presterar i princip likvärdigt eller bättre än de europeiska vinterdäcken, både som nya och slitna.

  • 25.
    Hjort, Mattias
    et al.
    Swedish National Road and Transport Research Institute, Traffic and road users, Driver and vehicle.
    Eriksson, Olle
    Swedish National Road and Transport Research Institute, Infrastructure, Infrastructure maintenance.
    Bruzelius, Fredrik
    Swedish National Road and Transport Research Institute, Traffic and road users, Driving Simulation and Visualization.
    Comprehensive study of the performance of winter tires on ice, snow, and asphalt roads: The influence of tire type and wear2017In: Tire Science and Technology, ISSN 0090-8657, Vol. 45, no 3, p. 175-199Article in journal (Refereed)
    Abstract [en]

    This work presents a comprehensive study of the performance of winter tires on snow, ice, and asphalt. A set of 77 different winter tires were carefully selected for the study. Of these, 27 were new and 50 were worn from real traffic use. All three tire types for winter conditions (Nordic, European, and studded) were represented. All tires have been tested using a mobile tire-testing device for snow and asphalt and using a stationary tire-testing facility for ice. Both devices recorded the tire forces and motions, enabling a close to complete stationary characterization of the tires. In addition, 42 of the tires were tested on a passenger car, where brake performance was evaluated for the three different road conditions. This enables a comparative study of performance between tire types and wear for various winter road conditions. The results suggest that the recorded data represent real vehicle performance. Some conclusions from the measurements are that the effect of wear is consistent between the tire groups and that the performance degradation is most noticeable on studded tires on ice and on European tires on snow.

  • 26.
    Hjort, Mattias
    et al.
    Swedish National Road and Transport Research Institute, Traffic and road users, Driver and vehicle.
    Gustafsson, Susanne
    Swedish National Road and Transport Research Institute, Traffic and road users, Traffic Safety and Traffic System.
    Henriksson, Per
    Swedish National Road and Transport Research Institute, Society, environment and transport, Mobility, actors and planning processes.
    Forsman, Åsa
    Swedish National Road and Transport Research Institute, Traffic and road users, Traffic safety, society and road-user.
    Tunga lastbilars däckanvändning och olycksrisk vintertid2017Report (Other academic)
    Abstract [en]

    In Sweden, it is today regulated that winter tyres must be used on the drive axle of heavy vehicles (total weight in excess of 3,500 kg) during the winter season period, December 1 to March 31, in case of winter conditions. This requirement is based entirely on accessibility, and it is considered that winter tyres on the drive axle provides better conditions for heavy vehicles to go forward in icy and snowy conditions. Previous accident risk studies have not been able to demonstrate that the use of winter tyres instead of summer tyres for heavy vehicles in winter could lead to reduced risk of accidents. In Norway and Finland, the regulations on tyre use for heavy vehicles in winter time has recently been revised. Prior to a discussion of possible regulations in Sweden on winter tyres also on other axles, there is reason to update the previous accident risk studies. The purpose of this study has been to calculate the risk of accidents on ice/snow conditions for comparison between summer and winter tires for heavy trucks. The study was performed according to the method previously used in the VTI studies conducted in 2000 and 2008. This meant that two questionnaires were sent out by the end of the winter 2015/2016. One survey to analyse the vehicle mileage on ice/snow conditions with different combinations of tires, and one questionnaire directed solely to the vehicle owners whose vehicles according Strada during the winter season have been involved in an injury accident. Accident risk calculations were limited to vehicles with a total weight of 16 tons.

  • 27.
    Hjort, Mattias
    et al.
    Swedish National Road and Transport Research Institute, Traffic and road users, Vehicle technology and simulation.
    Jansson, Jonas
    Swedish National Road and Transport Research Institute, Traffic and road users, Vehicle technology and simulation.
    Handling of buses on slippery roads during the influence of side wind: A study of the effects of different tyres2010In: Accident Analysis and Prevention, ISSN 0001-4575, E-ISSN 1879-2057, Vol. 42, no 3, p. 972-977Article in journal (Refereed)
    Abstract [en]

    Accident statistics assembled by the Swedish National Road and Transport Research Institute (VTI) have shown that buses are overrepresented when it comes to accidents on icy and snowy roads. For a better understanding of the problem, the performance of modern summer and winter tyres on winter road conditions had to be assessed. The objective of this work has been to go beyond standard road grip studies, and instead investigate how the driver's possibility to deal with one challenging situation depends on the tyres and tyre configuration. This paper describes a novel methodology where measurements with different tyres on ice in VTI's tyre test facility, enabled a simulator study for evaluating the impact of different tyre characteristics when driving in conditions with strong side wind on a slippery road.

    The main results of the study are: to deal with strong side wind, good front wheel grip is most important, and while non-studded winter tyres provided little or no improvement over summer tyres, studded winter tyres significantly reduced the risk to run off the road. Furthermore, it is very difficult for the drivers to judge, beforehand, whether a vehicle with a particular tyre configuration will perform good or bad.

  • 28.
    Hjort, Mattias
    et al.
    Swedish National Road and Transport Research Institute, Traffic and road users, Vehicle technology and simulation.
    Kharrazi, Sogol
    Swedish National Road and Transport Research Institute, Traffic and road users, Vehicle technology and simulation.
    Eriksson, Olle
    Swedish National Road and Transport Research Institute, Infrastructure, Infrastructure maintenance.
    Hjälmdahl, Magnus
    Swedish National Road and Transport Research Institute, Traffic and road users, Human-vehicle-transport system interaction.
    Limit handling in a driving simulator2015Report (Other academic)
    Abstract [en]

    The purpose of this work has been to investigate how the driving simulator performs at the handling limit of a vehicle and improve its function so that the simulator feels and behaves more like a real vehicle when driving on the limit. Tests were performed with a Volvo S40, the same vehicle model for which the driving simulator vehicle dynamics model is based upon. Based on these test results the vehicle model that is currently used in VTI’s driving simulator III was modified in order to better simulate vehicle characteristics when driving on the handling limit. A method for validation of handling characteristics was developed. The method is based on the double lane change manoeuvre, and comprise a subjective and an objective part. The method was regarded to work well, and the validation tests showed that the modified vehicle model closer captures the understeer and time lag properties of a real Volvo S40 compared to the original model. Still, additional improvements need to be made before the model can be regarded as fully useful for on-the-limit driving situations.

  • 29.
    Hjort, Mattias
    et al.
    Swedish National Road and Transport Research Institute, Traffic and road users, Vehicle technology and simulation.
    Kharrazi, Sogol
    Swedish National Road and Transport Research Institute, Traffic and road users, Vehicle technology and simulation.
    Eriksson, Olle
    Swedish National Road and Transport Research Institute, Infrastructure, Infrastructure maintenance.
    Hjälmdahl, Magnus
    Swedish National Road and Transport Research Institute, Traffic and road users, Human-vehicle-transport system interaction.
    Andersson Hultgren, Jonas
    Swedish National Road and Transport Research Institute, Traffic and road users, Vehicle technology and simulation.
    Validating on-the-limit properties of a driving simulator2014In: New development in driving simulation design and experiments: Driving simulation conference Europe 2014 proceedings, 2014Conference paper (Refereed)
    Abstract [en]

    The paper describes a validation model for both subjective and objective comparison of on-the-limit properties of a driving simulator. VTI moving base driving simulator, SIM III, has been used with three different versions of VTI’s vehicle model, for validation toward field tests involving double lane change manoeuvres. Methods for handling evaluation suggested in the literature were adapted to our circumstances. The results are encouraging, although we found some limitations with respect to the objective evaluations that need to be addressed in future studies.

  • 30.
    Hjort, Mattias
    et al.
    Swedish National Road and Transport Research Institute, Traffic and road users, Vehicle technology and simulation.
    Niska, Anna
    Swedish National Road and Transport Research Institute, Infrastructure, Infrastructure maintenance.
    Kan dubbdäck på cykeln minska singelolyckorna?: friktionstester av cykeldäck i VTI:s stationära däckprovningsanläggning2015Report (Other academic)
    Abstract [en]

    The purpose of this project was to define a useful methodology for comparing the ice grip of different bicycle tyres and to perform initial measurements. The long term objective is to set up recommendations to winter cyclists regarding bicycle tyres based on measurements performed according to the defined methodology. Measurements were done on smooth slippery ice using two regular (non-studded) bicycle tyres and four studded tyres of different brands and models. The tests were carried out in the VTI tyre test facility (TTF). The TTF is a unique indoor flat track machine for tyre tests on ice or asphalt pavement. This construction enables measurement of frictional forces under controlled conditions both when braking and steering. The TTF has been used for several years when testing tyres for both passenger cars and heavy vehicles, but to be able to test bicycle tyres some modifications of the equipment were necessary. The defined test method proved to be suitable for comparing studies. The measurements showed that studded tyres improve the grip on ice compared to regular bicycle tyres, but there can be differences in performance between different types of studded tyres. A larger number of studs is not necessarily related to a better grip on ice. When braking with locked wheel the frictional forces measured, were up to 2.5 times higher with a studded tyre compared to a non-studded tyre. In addition, studded tyres generally generate greater frictional forces when steering on ice compared to non-studded tyres. In general, a lower tyre pressure slightly increases braking and steering forces, but an optimal tyre pressure might be necessary in order to achieve the best possible performance from a studded bicycle tyre. Based on the results so far, cyclists should be recommended to use studded tyres when cycling during winter conditions. With an improved grip on ice and a better braking stability, there are safety benefits to be made.

  • 31.
    Hjort, Mattias
    et al.
    Swedish National Road and Transport Research Institute, Traffic and road users, Driver and vehicle.
    Niska, Anna
    Swedish National Road and Transport Research Institute, Infrastructure, Infrastructure maintenance.
    Mätning av cykeldäcks friktionsegenskaper som underlag för simuleringsstudier2018Report (Other academic)
    Abstract [en]

    In this project measurements of a bicycle tyre on an asphalt surface have been carried out in the VTI stationary tyre testing facility, in order to provide slip curves describing friction properties of the tyre. The measurement results have then been used to obtain tyre parameters for simulation purposes. The following tyre parameters have been measured: cornering stiffness, camber stiffness, brake slip stiffness and lateral relaxation length.

    The tested tyre generated a maximum friction level of approximately 1.0 on the asphalt. Typical values of the tyre parameters were: normalized cornering stiffness 0.3; standardized camber stiffness 0.01; standard brake slip stiffness 250. Compared to the few previously published measurements on bicycle tyres, cornering stiffness was generally about 50 percent higher than previously reported. The values for camber stiffness correspond well to the values shown by a racing tyre study but are 25–50 percent lower than the values measured on more normal tyres in another study. For brake slip stiffness there are no previous measurements to compare with. Measurement of the lateral relaxation length was unfortunately affected by problems with the measuring equipment and we could not determine the relaxation length with the desired accuracy. From the measurements, we estimate the relaxation length to 200–300 mm for the tested tire, which is a factor 2–3 to greater than reported in the only earlier study that measured relaxation length for bicycle tyres.

  • 32.
    Hjort, Mattias
    et al.
    Swedish National Road and Transport Research Institute, Traffic and road users, Vehicle technology and simulation.
    Sandin, Jesper
    Swedish National Road and Transport Research Institute, Traffic and road users, Human-vehicle-transport system interaction.
    Trafiksäkerhetseffekter vid införande av längre och tyngre fordon: en kunskapsöversikt2012Report (Other academic)
    Abstract [en]

    This review concerns potential traffic safety effects from the introduction of longer and heavier trucks than those currently allowed in Sweden. For this purpose, a summary of results from accident studies, literature summaries and in-depth studies of fatal accidents involving heavy trucks done in the past few years was made. In addition, a focus group study with truck drivers was conducted and results from a parallel VTI study concerning overtaking of longer trucks have also been included in order to give an overall picture of the possible traffic safety effects associated with the introduction of longer and heavier trucks in Sweden.

    Following are some of the recommendations, based on the aspects that have been addressed in this report:

    • Longer and heavier vehicles should mainly operate on main roads where it is possible to overtake heavy vehicles without fear of oncoming traffic. Longer and heavier vehicles should operate as little as possible in urban areas.
    • •Longer and heavier vehicles shall be constructed for good stability, and be equipped with Electronic Brake System (EBS).
    • •Longer and heavier vehicles puts greater demand on tires, brakes and especially maintenance and inspection.
    • •Driver fatigue is a cause of an essential part of single-vehicle accidents with heavy vehicles. Drive and rest times may be harder to keep with the extra-long vehicles if rest areas, which are already today overcrowded along certain roads, are not extended.
    • •The signs of the transition distance on 2+1 roads should be reviewed to possibly reduce the risk of dangerous situations and emergencies caused by overtaking of heavy vehicles.
    • •Additional field studies on two-lane roads are necessary to determine whether there is a higher risk to overtake a 30 m long vehicle compared to overtaking a conventional heavy truck.
  • 33.
    Hjort, Mattias
    et al.
    Swedish National Road and Transport Research Institute, Traffic and road users, Vehicle technology and simulation.
    Wiklund, Mats
    Swedish National Road and Transport Research Institute, Infrastructure, Infrastructure maintenance.
    Öberg, Gudrun
    Swedish National Road and Transport Research Institute, Infrastructure, Infrastructure maintenance.
    Bus accidents in wintertime2010In: PIARC 2010 XIII International Winter Road Congress, February 8-11, 2010, Quebec, Canada: proceedings, 2010Conference paper (Refereed)
    Abstract [en]

    Buses in Sweden have a low accident risk. However, statistics from 1996 - 2002 indicate that the number of bus accidents in Sweden with personal injuries have been increasing by 4% yearly. Buses also have a higher percentage of accidents that occur on ice/snow covered roads than other vehicles. In Sweden passenger cars must be equipped with winter tyres during the winter period. There is no such regulation for heavy vehicles, and many buses are using summer tyres all around the year. The present project had the purpose of looking at the bus-winter problem in more detail, with the main focus on tyres. Four different studies were carried out: tyre tests, focus group discussions, driving simulator tests and an accident study. Here is given a short summary concerning methods and conclusions of each sub project.

    Tyre tests on smooth ice did not show any significant difference between summer tyres and non-studded winter tyres, while studded tyres exhibits a better ice grip than non-studded tyres. Nor did driving simulator tests with driving on ice covered road under the influence of heavy wind from the side show a difference between summer tyres and non-studded winter tyres. Also in these tests studded tyres were superior to non-studded. Accident statistics indicate that buses with summer tyres on the steering axle and winter tyres on the drive axle have the lowest estimated accident risk, which is in accordance with the results in a previous study. The results are however not statistically significant due the low number of accidents. Three focus groups were carried out and the importance of the tyres for traffic safety during winter was discussed. It is however hard from the gathered discussion material to estimate just how important the tyres really are. The results do not warrant a winter tyre regulation for heavy vehicles, and a restriction of the use of studded tyres for buses would probably have negative consequences on traffic safety.

  • 34.
    Jacobson, Jan
    et al.
    SP.
    Eriksson, Henrik
    SP.
    Hérard, Jacques
    SP.
    Leandersson-Olsson, Susanna
    VTEC.
    Nordström, Lars
    VTEC.
    Basso, Rafael
    VTEC.
    Fredriksson, Krister
    VTEC.
    Dalmau, Josep Maria
    IDIADA.
    Aparicio, Andres
    IDIADA.
    Baures, Sebastien
    IDIADA.
    Munoz, Oscar
    Swedish National Road and Transport Research Institute.
    Lesemann, Micha
    ika.
    Zlocki, Adrian
    ika.
    Lützow, Jörn
    ika.
    Fahrenkrog, Felix
    ika.
    Bruzelius, Fredrik
    Swedish National Road and Transport Research Institute, Traffic and road users, Vehicle technology and simulation.
    Andersson, Håkan
    Swedish National Road and Transport Research Institute.
    Hjort, Mattias
    Swedish National Road and Transport Research Institute, Traffic and road users, Vehicle technology and simulation.
    Westhoff, Daniel
    SICK.
    Vesco, Mauro
    CRF.
    Camuffo, Isabella
    CRF.
    Marenco, Silvano
    CRF.
    Murdocco, Vincenzo
    CRF.
    Sanchez, Javier
    RBTK.
    Isasi, Lucia
    RBTK.
    Final testing protocols2011Report (Other academic)
    Abstract [en]

    This report is the final document summarizing the inspection and testing protocols of the eVALUE project. It describes principles, inspection protocols and testing protocols for performance testing of ICT-based safety systems. The inspection protocols (published earlier in D2.2) and the testing protocols introduced in D3.1 are replaced by the ones in D3.2. The older versions are obsolete and should be disregarded. The inspection protocols cover the definition of the test vehicle, HMI aspects, environmental conditions, and functional safety. The inspection protocols are used to prepare for the physical tests as well as evaluating the performance of the vehicle. The testing protocols address longitudinal, lateral, and stability-oriented traffic scenarios. The longitudinal scenarios include a pedestrian crossing the road in front of the vehicle, or the situation where a driver approaches a stationary queue of cars. Involuntarily lane departures and cars in the blind spot during a lane change are situations covered by the lateral scenarios. Exiting a highway, avoiding an obstacle, and braking on a partially ice-covered road surface are examples of traffic scenarios related to stability.

  • 35.
    Jacobson, Torbjörn
    et al.
    Swedish National Road and Transport Research Institute.
    Hjort, Mattias
    Swedish National Road and Transport Research Institute.
    Polering av asfaltbeläggning2008Report (Other academic)
    Abstract [en]

    In many countries, where studded tyres are prohibited, the traffic polishing of the coarse aggregate in the wearing courses is a problem to a rather great extent. In those countries there are often regulations on the aggregate polishing value. In Sweden, where the use of studded tyres is extensive, the micro texture of the aggregate in the surface of the wearing courses increases during the winter season. Therefore, there have been few problems with low wet friction levels in Sweden. However, the increased use of wear resistant aggregates and stone mastic asphalt together with lightweight studs has led to a reduced amount of wear. During later years, a problem with low friction levels has been noticed in wear resistant surface courses during late summer and fall, especially at high trafficked roads with a complicated geometry. Measurements have shown that the friction level can be reduced rather quickly on surfaces with aggregates that are disposed for polishing and low wet friction related accidents have been reported. This report is a knowledge survey covering polishing, friction and to some extent surface texture and wear caused by studded tyres. Experiences from friction measurements mainly in Stockholm and Gothenburg have been compiled in this report. A review of testing methods and existing requirements is also presented in the report. Friction measurements have been carried out with two friction measurement equipments, SAAB Friction Tester and BV12, where the measuring speed, time of the year, the amount of water film thickness, the type of tyre and tyre pressure have been varied.

  • 36.
    Jansson, Andreas
    et al.
    Swedish National Road and Transport Research Institute, Traffic and road users, Vehicle technology and simulation.
    Olsson, Erik
    Swedish National Road and Transport Research Institute, Traffic and road users, Vehicle technology and simulation.
    Linder, Jonas
    Linköpings Universitet.
    Hjort, Mattias
    Swedish National Road and Transport Research Institute, Traffic and road users, Vehicle technology and simulation.
    Developing of a Driver Model for Vehicle Testing2014In: Proceedings of the 14th International Symposium on Advanced Vehicle Control (AVEC), Tokyo, September 2014., 2014Conference paper (Refereed)
    Abstract [en]

    There is today no established automated method for testing vehicles or tyres, and the most common option is using professional drivers for this purpose. The tests are supposed to be fair and repeatable, which means using human drivers for these kinds of vehicle testing is not an option. Using a steering robot modelled to drive as a human is therefore preferable. The approach described in this paper shows how a driver model can be created by using a control algorithm based on gathered data from human drivers performing double lane change (DLC) manoeuvres in a simulator. The implemented controller shows how human drivers’ behaviors can be captured using control theory.

  • 37.
    Kharrazi, Sogol
    et al.
    Swedish National Road and Transport Research Institute, Traffic and road users, Vehicle technology and simulation.
    Hjort, Mattias
    Swedish National Road and Transport Research Institute, Traffic and road users, Vehicle technology and simulation.
    Bruzelius, Fredrik
    Swedish National Road and Transport Research Institute, Traffic and road users, Vehicle technology and simulation.
    Andersson, Håkan
    Testing Vehicle Performance on Snow Using Sine with Dwell2014In: Proceedings of the 14th International Symposium on Advanced Vehicle Control (AVEC), Tokyo, September 2014., 2014Conference paper (Refereed)
    Abstract [en]

    Measuring and evaluating vehicle and tire performance in winter conditions are highly motivated by accident statistics. The present paper investigates use of the sine with dwell maneuver in this context. Various aspects of winter testing is discussed and illustrated with test track measurements, such as test repeatability and trade-off between stability and maneuverability. An evaluation procedure is presented and demonstrated with the classical issue of which axle to choose for the worst set of tires.

  • 38. Kusachov, Artem
    et al.
    Bruzelius, Fredrik
    Swedish National Road and Transport Research Institute, Traffic and road users, Driver and vehicle.
    Hjort, Mattias
    Swedish National Road and Transport Research Institute, Traffic and road users, Driver and vehicle.
    Jacobson, Bengt J. H.
    Chalmers Tekniska Högskola.
    A Double Interaction Brush Model for Snow Conditions2019In: TIRE SCIENCE AND TECHNOLOGY, ISSN 0090-8657, Vol. 47, no 2, p. 118-140Article in journal (Refereed)
    Abstract [en]

    Commonly used tire models for vehicle-handling simulations are derived from the assumption of a flat and solid surface. Snow surfaces are nonsolid and may move under the tire. This results in inaccurate tire models and simulation results that are too far from the true phenomena. This article describes a physically motivated tire model that takes the effect of snow shearing into account. The brush tire model approach is used to describe an additional interaction between the packed snow in tire tread pattern voids with the snow road surface. Fewer parameters and low complexity make it suitable for real-time applications. The presented model is compared with test track tire measurements from a large set of different tires. Results suggest higher accuracy compared with conventional tire models. Moreover, the model is also proven to be capable of correctly predicting the self-aligning torque given the force characteristics.

  • 39.
    Linder, Astrid
    et al.
    Swedish National Road and Transport Research Institute, Traffic and road users, Traffic safety, society and road-user.
    Dukic, Tania
    Swedish National Road and Transport Research Institute, Traffic and road users, Human-vehicle-transport system interaction.
    Hjort, Mattias
    Swedish National Road and Transport Research Institute, Traffic and road users, Vehicle technology and simulation.
    Matstoms, Ylva
    Swedish National Road and Transport Research Institute.
    Mårdh, Selina
    Swedish National Road and Transport Research Institute, Traffic and road users, Human-vehicle-transport system interaction.
    Sundström, Jerker
    Swedish National Road and Transport Research Institute, Traffic and road users, Human-vehicle-transport system interaction.
    Vadeby, Anna
    Swedish National Road and Transport Research Institute, Traffic and road users, Traffic safety, society and road-user.
    Wiklund, Mats
    Swedish National Road and Transport Research Institute, Infrastructure, Infrastructure maintenance.
    Östlund, Joakim
    Swedish National Road and Transport Research Institute.
    Methods for the evaluation of traffic safety effects of Antilock Braking System (ABS) and Electronic Stability Control (ESC): a literature review2007Report (Other academic)
    Abstract [sv]

    In today's vehicles, active safety systems are introduced addressing a large variety of safety issues such as providing optimal stability control, braking effect, preventing spin and rollover, as well as collision avoidance, to mention just a few. In this study a literature review was performed in order to establish how the traffic safety performances of active safety systems with focus on Antilock Braking System (ABS) and Electronic Stability Control (ESC) are assessed. The areas covered were statistical evaluation, testing and driver behaviour. The literature review showed that in particular statistical methods, based on odds ratios, had been used in order to evaluate the traffic safety effect. In order to evaluate the effect of ESC in physical testing there are several test methods described in this report. Estimations of driver behaviour effects have been carried out by surveys among vehicle owners. Experiments performed in field or in simulator have also been found in the literature. From EU projects a variety of measures and test methods are available for assessment of driver behavioural effects.

  • 40.
    Linder, Astrid
    et al.
    Swedish National Road and Transport Research Institute.
    Dukic, Tania
    Swedish National Road and Transport Research Institute.
    Hjort, Mattias
    Swedish National Road and Transport Research Institute.
    Mårdh, Selina
    Swedish National Road and Transport Research Institute.
    Sundström, Jerker
    Swedish National Road and Transport Research Institute.
    Vadeby, Anna
    Swedish National Road and Transport Research Institute.
    Methods for evaluation of Electronic Stability Control (ESC): a literature review2007Conference paper (Refereed)
  • 41.
    Ljung Aust, Mikael
    et al.
    Volvo cars.
    Engström, Johan
    Volvo technology.
    Viström, Matias
    Saab automobile.
    Nåbo, Arne
    Saab automobile.
    Bolling, Anne
    Swedish National Road and Transport Research Institute, Traffic and road users, Vehicle technology and simulation.
    Hjort, Mattias
    Swedish National Road and Transport Research Institute, Traffic and road users, Vehicle technology and simulation.
    Källgren, Laban
    Swedish National Road and Transport Research Institute, Traffic and road users, Vehicle technology and simulation.
    Effects of forward collision warning, initial time headway and repeated scenario exposure on driver response in emergency lead vehicle braking scenarios2011Report (Other academic)
    Abstract [en]

    To address the research questions, acritical lead vehicle braking scenario and anFCW system was developed and pilot tested in Saab’s fixed based driving simulator in Trollhättan. After piloting, the scenario was implemented in VTI’s moving base simulatorin Linköping, and the effects,of FCW presence, two different initial time headways at visual distraction task onset and repeated scenario exposure, on driver response timeswere examined.The study showed significant effects of FCW and repeated scenario exposure on response times. Moreover, these effects were not additivei.e. a significant interaction between the two was found. There was also a significant effect on responsetimes ofinitial time headway at onset of the visual distraction task. In addition, an interaction between initial time headway and repeated scenario exposure was found for drivers with FCW, but not for drivers without FCW. A second objective of the project was to compare the extent to which the VTI moving base simulator with motion cues generates similar driver responses(quantitatively and qualitatively)as the static simulator set-up at Saab. In general, theresults from this project have important implications for the interpretation of driver performance in experimental settings, particularlywhen aiming toevaluate safety-related in-vehicle information and warning technologies. For onething,they pose a general question markaround the generalizabilityof results to real world events. Second, a future prerequisite for FCW studies should probably be that test drivers have a previous level of system exposure level which matchesthat of real world drivers encountering typical critical events. Also, tuning the initialtime headwayat distraction task onsetin the experimentalsetting to real world conditions is of critical importance.

  • 42.
    Niska, Anna
    et al.
    Swedish National Road and Transport Research Institute, Infrastructure, Infrastructure maintenance.
    Blomqvist, Göran
    Swedish National Road and Transport Research Institute, Society, environment and transport, Environment.
    Hjort, Mattias
    Swedish National Road and Transport Research Institute, Traffic and road users, Driver and vehicle.
    Cykelvägars friktion: mätningar i fält i jämförelse med cykeldäcks friktion på olika underlag i VTI:s däckprovningsanläggning2018Report (Other academic)
    Abstract [en]

    Skidding is a common cause for cyclists getting seriously injured in traffic. Neither requirements nor prescribed friction measurement methods for cycleways have been based on the performance of bicycles. There is therefore a need for increased knowledge regarding the friction characteristics of bicycle tyres and the traction between a bicycle tyre and the road surface under different conditions. In this project we have compiled measurements with VTI's portable friction tester, PFT, on cycleways with a variety of road conditions. To relate the PFT friction values to the friction of bicycle tyres, we have also made comparative measurements with bicycle tyres in VTI's stationary tyre testing facility. These show a very good match between the PFT friction values and the maximum lateral friction available for a bicycle tyre. This means that the PFT friction values recorded on cycleways can also be said to represent the friction that a bicycle tyre would perform on the same surface. Our friction measurements on cycleways show that the skid resistance is affected by the road condition, the road surface material, as well as road markings and manhole-covers. Ice and snow cause a significantly lower friction level than at bare conditions. Differences in road conditions mean that different types of cycling infrastructure and different winter maintenance methods result in different friction levels. This means that there may be large variations in friction along one and the same cycle route. The surprise effect and thus the accident risk can then be great. Not only snow, ice and grit, but also leaves, clay and other dirt on the surface might lead to a reduced skid resistance. For the safety of cyclists, it is important to inform about where a slippery condition can occur and to adjust anti-icing actions, road design and construction according to that knowledge.

  • 43.
    Nåbo, Arne
    et al.
    Swedish National Road and Transport Research Institute, Traffic and road users, Driving Simulation and Visualization.
    Andhill, Carl Johan
    Dynagraph.
    Blissing, Björn
    Swedish National Road and Transport Research Institute, Traffic and road users, Driving Simulation and Visualization.
    Hjort, Mattias
    Swedish National Road and Transport Research Institute, Traffic and road users, Driver and vehicle.
    Källgren, Laban
    Swedish National Road and Transport Research Institute, Traffic and road users, Driving Simulation and Visualization.
    Known Roads: real roads in simulated environments for the virtual testing of new vehicle systems2016Report (Other academic)
    Abstract [en]

    This publication presents a project aiming to develop virtual representations of real roads for use in driving simulators. The development was done in order to enable assessments of new systems on existing and well known roads in a driving simulator, and will increase the external validity of virtual testing. Furthermore, the usage of the virtual model of such roads makes the simulator results better comparable to earlier performed or later following road tests. The roads connecting Göteborg-Borås-Alingsås-Göteborg were selected. The purpose for this is due to their proximity to the vehicle industry in west Sweden and to the test tracks “Hällered” and “AstaZero”. However, the tools and methods developed can be used to build a virtual representation of any other road through a surrounding landscape and/or more urban environment. The project was carried out in steps, starting with data collection (investigation and assessment of available data from different sources as well as measurement of road properties) followed by data treatment (remove irrelevant data and errors, filtering, etc.), modelling (mathematical description of road properties) and simulation (selection of data formats for real time simulation).

  • 44.
    Said, Safwat F.
    et al.
    Swedish National Road and Transport Research Institute, Infrastructure, Pavement Technology.
    Hakim, Hassan
    Swedish National Road and Transport Research Institute, Infrastructure, Pavement Technology.
    Oscarsson, Erik
    Lunds Universitet.
    Hjort, Mattias
    Swedish National Road and Transport Research Institute, Traffic and road users, Vehicle technology and simulation.
    Prediction of flow rutting in asphalt concrete layers2011In: The international journal of pavement engineering, ISSN 1029-8436, E-ISSN 1477-268X, Vol. 12, no 6, p. 519-532Article in journal (Refereed)
    Abstract [en]

    This paper evaluates an approach for predicting rut formation in asphalt concrete (AC) layers. The approach is based on a linear viscoelastic model for predicting permanent vertical strain in AC layers subjected to a moving load. The input data are tyre pressure, loading speed, lateral wandering of loading wheel, shear modulus and phase angle of AC layer. The analytical approach takes into consideration the change in material characteristics in respect of temperature and changes in the air void content of AC layers due to repeated loading. The approach is verified by a full-scale accelerated loading test at different temperatures. The approach has shown good agreement as regards the prediction of flow rutting in AC layers. In addition, the approach is capable of calculating rutting profiles including the upheaval, which is important for estimating rut depth.

  • 45.
    Sandberg, Ulf
    et al.
    Swedish National Road and Transport Research Institute, Society, environment and transport, Environment.
    Hjort, Mattias
    Swedish National Road and Transport Research Institute, Traffic and road users, Vehicle technology and simulation.
    Relation between tyre/road noise and ice snow friction of winter tyres2013Conference paper (Refereed)
    Abstract [en]

    It is often assumed that low noise emission from car tyres implies a sacrifice of frictional properties. This study explores the relation between tyre/road noise with friction coefficients on ice and snow surfaces for a number of winter tyres, designed either for central European or for Nordic winter roads.

    Measurements of noise were made by the coast-by method in accordance with the EU regulation on a test track having an ISO surface. Measurements of ice friction were made on a long straight climate controlled indoor test track in Sweden which was covered by ice. Snow friction tests were made with a car braking on an outdoor test track in northern Finland. Ten different tyres were tested for all the conditions.

    The results show that the correlation between noise levels and ice friction coefficients is consistently negative, which means that tyres having lower noise have higher friction. The tested tyres ranked with respect to noise in this order (from high to low noise level): summer tyres, tyres designed for central Europe winter roads, and tyres designed for Nordic winter roads. The relation between noise level and friction on snow was less clear, but it was obvious that the summer tyres were much worse than the winter tyres.

    It is concluded that the design principles for winter tyres at large are favourable also for achieving low noise emission.

  • 46.
    Thomson, Robert William
    et al.
    Swedish National Road and Transport Research Institute, Traffic and road users, Traffic safety, society and road-user.
    Sandin, Jesper
    Swedish National Road and Transport Research Institute, Traffic and road users, Human-vehicle-transport system interaction.
    Bagdadi, Omar
    Swedish National Road and Transport Research Institute, Traffic and road users, Human-vehicle-transport system interaction.
    Hjort, Mattias
    Swedish National Road and Transport Research Institute, Traffic and road users, Vehicle technology and simulation.
    Augusto, Bruno
    Swedish National Road and Transport Research Institute, Traffic and road users, Vehicle technology and simulation.
    Andersson, Håkan
    Swedish National Road and Transport Research Institute, Infrastructure, Crash safety.
    EDR Pre-Crash Data: Potential For Applications In Active Safety Testing2013In: Proceedings of the 23rd International Technical Conference on the Enhanced Safety of Vehicles, May 2013, Seoul, 2013, article id 13-0414Conference paper (Refereed)
    Abstract [en]

    Passive safety testing has been based on accident research where objective physical evidence can be compiled and analysed when establishing technical test requirements. Active safety tests pose new challenges because objective data is more difficult to obtain. Until pre-crash variables became available in Event Data Recorders (EDR), the only sources of pre-crash vehicle motions were tire marks or witness statements. Both data sources have limitations since they may not always be available and require interpretation by the analyst. The pre-crash EDR data variables provide an objective source of data to active safety test development. However, the suitability of the data has not been thoroughly investigated in the published literature.

    The review of existing data shows that the variables identified in the new EDR requirement in FMVSS 563 are useful but incomplete for a comprehensive analysis of vehicle dynamics manoeuvres prior to a crash. In particular, the absence of vehicle yaw rate reduces the positioning accuracy of the vehicle in reconstructions. The objective data in the limited cases were used to compile the frequency of pre-crash braking and steering, and when possible, the magnitude of these driver inputs. Active Safety test development will benefit with more EDR analysis but the older data that does not conform to Part 563 has limited application.

  • 47.
    Wiklund, Mats
    et al.
    Swedish National Road and Transport Research Institute.
    Hjort, Mattias
    Swedish National Road and Transport Research Institute.
    Kartläggning av bussolyckor vintertid2006Report (Other academic)
    Abstract [sv]

    In an earlier VTI study from 1997 in which the tyre usage for heavy vehicles was surveyed, statistics suggested that buses may have a larger problem with slippery roads compared to other vehicle types, like personal cars and heavy trucks. The statistical data was however not large enough to conclude that this is the case. Therefore, the present study was conducted with the aid of accident data for various vehicle types collected from VITS, the information system for traffic safety of the Swedish Road Administration. The information concerns accidents that occurred during seven winters 1995/1996-2001/2002. Corresponding information has also been collected from Finnish accident data. All of the statistical analyses in this study indicate problems with traffic safety for buses on icy or snowy roads. However, none of these results are statistically significant. The statistical uncertainty in these results stems from a low number of accidents, but also from a lack of information regarding the actual travelled distance on different road conditions for the vehicles. It is probably necessary to know the travelled distance on different road conditions for buses to make a conclusion about accident probability for buses on winter roads. We will therefore make inquiries to bus companies in Sweden during the winters 2005/2006 and 2006/2007 concerning the travelled distances on different road conditions to complete the present study.

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