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Driving Faster or Slower?: Speed Changes and Judged Effects on Fuel Consumption
Swedish National Road and Transport Research Institute, Traffic and road users, Human-vehicle-transport system interaction. Stockholms universitet.
Stockholms universitet.
(English)Article in journal (Refereed) Submitted
Abstract [en]

Greenhouse gas emissions from the transport sector continue to increase. Lower speeds on roads would reduce fuel consumption and thereby emissions. Drivers choose the speed of their vehicles, but do they realize the full benefit of a reduced speed on fuel consumption? In a set of questionnaires, professional truck drivers and student groups were asked to judge fuel consumption at decreasing and increasing speeds. The truck drivers underestimated the amount of fuel saved by decreasing speed, but made more accurate judgments of fuel lost at increasing speeds. Student groups made better judgments of fuel saved at decreasing speeds than the truck drivers. It is important that drivers understand the full benefit of a reduced speed on fuel consumption. This may affect both preferred driving speed and attitudes towards lower speed limits. Some policy suggestions on how to promote environmentally efficient driving were discussed.

Keyword [en]
Fuel consumption, Speed, Choice, Decrease, Judgement (road user)
National Category
Psychology
Research subject
80 Road: Traffic safety and accidents, 841 Road: Road user behaviour
Identifiers
URN: urn:nbn:se:vti:diva-6834OAI: oai:DiVA.org:vti-6834DiVA: diva2:707792
Available from: 2015-11-25 Created: 2014-03-25 Last updated: 2016-01-22Bibliographically approved
In thesis
1. On Physical Relations in Driving: Judgements, Cognition and Perception
Open this publication in new window or tab >>On Physical Relations in Driving: Judgements, Cognition and Perception
2014 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Drivers need to make judgements of physical relationships related to driving speed, such as mean speed, risks, travel time and fuel consumption, in order to make optimal choices of vehicle speed. This is also the case for the general public, politicians and other stakeholders who are engaged in traffic issues. This thesis investigates how drivers’ judgements of travel time (Study I and II), fuel consumption (Study III) and mean speed (Study IV) relate to actual physical measures.

A cognitive time-saving bias has been found in judgements of travel time. The time saving bias implies that people overestimate the time saved when increasing speed from a high speed and underestimate the time saved when increasing speed from a low speed. Previous studies have mainly investigated the bias from a cognitive perspective in questionnaires. In Study I the bias was shown to be present when participants were engaged in a driving simulator task where participants primarily rely on perceptual cues. Study II showed that intuitive time saving judgements can be debiased by presenting drivers with an alternative speedometer that indicate the inverted speed in minutes per kilometre.

In Study III, judgements of fuel consumption at increasing and decreasing speeds were examined, and the results showed systematic deviations from correct measures. In particular, professional truck drivers underestimated the fuel saving effect of a decrease in speed. Study IV showed that subjective mean speed judgements differed from objective mean speeds and could predict route choice better than objective mean speeds. The results indicate that biases in these judgements are robust and that they predict behaviour.

The thesis concludes that judgements of mean speeds, time savings and fuel consumption systematically deviate from physical measures. The results have implications for predicting travel behaviour and the design of driver feedback systems.

Abstract [sv]

Förare bör göra bedömningar som relaterar till hastighet, såsom bedömningar av medelhastighet, risk, restid och bränsleåtgång. Dessa bedömningar är nödvändiga för att föraren ska kunna välja en optimal hastighet, men också för att allmänheten, politiker och andra intressenter som är involverade i trafikfrågor ska kunna fatta välgrundade beslut. Denna avhandling består av fyra delstudier där förares bedömningar av restid (Studie I och II), bränsleåtgång (Studie III) och medelhastighet (Studie IV) studeras i relation till faktiska fysikaliska mått.

Tidigare enkätstudier har påvisat ett kognitivt bias i tidsvinstbedömningar vid höga och låga hastigheter som påverkar mänskligt beteende. Studie I visade att detta bias också förekommer i en primärt perceptuell motorisk uppgift där förarna i studien kör i en körsimulator. Studie II visade att dessa intuitiva tidsbedömningar kan förbättras genom att köra med en alternativ hastighetsmätare i bilen som indikerar den inverterade hastigheten i minuter per kilometer istället för hastigheten i kilometer per timme.

I Studie III undersöktes bedömningar av bränsleåtgång vid hastighetsökningar och hastighetssänkningar, och resultaten visar att bedömningarna systematiskt avviker från faktisk bränsleåtgång. Ett intressant resultat var att lastbilsförare i allmänhet underskattade bränslebesparingen som kan göras till följd av en hastighetssänkning. Studie IV visade att subjektiva bedömningar av medelhastighet som avviker från objektiva medelhastigheter kan predicera vägval, vilket tyder på att systematiska fel i dessa bedömningar är robusta och kan predicera vägval.

Sammanfattningsvis visar avhandlingen hur bedömningar av medelhastighet, tidsvinst och bränsleåtgång systematiskt avviker från fysikaliska mått. Resultaten har betydelse för modellering av resebeteende och design av förarstödssystem.

Place, publisher, year, edition, pages
Stockholm: Department of Psychology, Stockholm University, 2014
Keyword
Driver, Driving (veh), Cognition, Behaviour, Choice, Speed, Fuel consumption, Route (itinerary), Thesis
National Category
Psychology
Research subject
Road: Traffic safety and accidents, Road: Road user behaviour
Identifiers
urn:nbn:se:vti:diva-6836 (URN)978-91-7447-855-6 (ISBN)
Public defence
2014-03-14, David Magnussonsalen (U31), Frescati Hagväg 8, Stockholm, 10:00 (English)
Opponent
Supervisors
Note

At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 2: Submitted. Paper 3: Submitted.

Available from: 2014-03-26 Created: 2014-03-25 Last updated: 2014-05-14Bibliographically approved

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