Relationship between fuel economy and safety outcomes

Monash University Accident Research Centre - Report #188 - 2002

Full report in .pdf format [470KB]

Authors:  N. Haworth and M. Symmons

Abstract:

This report examines the possible safety benefits from driving in a manner that results in lower fuel consumption and emissions. It attempts to assess the potential of promoting additional motivations to drive safely - better fuel economy and other environmental outcomes, and reduced running costs.

Reducing speeding, lower speed limits and modifying driving style were found to improve fuel economy and other environmental outcomes in addition to improving safety. Community attitude surveys suggest that there will be greater support for measures that aim to improve fuel economy than for those measures that attempt to reduce vehicle travel. In addition, reducing fuel consumption rate without requiring a change in vehicle choice may be more acceptable and more easily implemented in the short-term. Programs such as these that result in reduced fuel consumption in addition to safety are more likely to be implemented because the benefits (in terms of fuel cost savings) flow directly to the vehicle owner.

The case study found that the fuel consumption rate of crash-involved vehicles was higher than that of vehicles not involved in crashes and demonstrated the feasibility of this method. Comparisons before and after training in driving to reduce fuel consumption and analytical studies based on fleet data are recommended as measures of the safety effects of fuel-efficient driving. Studies of the effects of instructions in driving style have the potential to provide useful information about the best ways in which to bring about fuel-efficient driving.

Executive Summary

Both road safety and the environment are critically affected by the extent of the use of motor vehicles and the specific ways in which they are driven. This report examines the possible safety benefits from driving in a manner that results in lower fuel consumption and emissions. It attempts to assess the potential of promoting additional motivations to drive safely - better fuel economy and other environmental outcomes, and reduced running costs.

From an environmental perspective, fuel consumption results in the production of vehicle emissions which can be classified into air pollutants (which affect health) and greenhouse gases (which affect the environment). Fuel consumption also depletes stocks of non-renewable fossil fuels. Total fuel consumption can be decreased by reducing vehicle travel or by reducing fuel consumption rate (improving fuel economy). This report focuses on the safety effects of measures that improve fuel economy, rather than the effects of reduced vehicle travel. The scope of the report is confined to passenger cars and light trucks.

The safety benefits of driving in a manner that reduces fuel consumption

Driver behaviours that affect fuel consumption rate and safety include: choice of travel speed, smoothness of driving, choice of travel route, use of air conditioning and use of cruise control. Smoothness of driving and choice of travel route both affect fuel consumption rate by modifying the speed profile.

Reductions in travel speeds will result in crash savings in all scenarios. The reductions may be greatest in urban areas because of the significant representation of unprotected road users and because vehicles are better at protecting their occupants at urban speed levels. In urban areas, some fuel consumption and emissions reductions will follow from lower travel speeds but the bulk of the benefit will be to road safety. For open road travel, the crash savings associated with lower speeds are likely to be significant. The fuel consumption savings are likely to be greater than at urban speed levels.

Smoother driving has greater potential for reducing fuel consumption and emissions in urban areas than in open road travel. At the level of the individual vehicle, smoother driving can lead to greater reductions in fuel consumption than lower travel speeds in urban areas. The resulting reduction in emissions of air pollutants is expected to be greater than the reduction in greenhouse gas emissions. The environmental benefits of smoother driving may be greater than the road safety benefits but this is yet to be established.

More information is needed about the road safety effects of smoother driving. The possible effect on following distance of drivers attempting to maintain a steady speed (or avoid braking) has not been investigated. The nature of instructions to be given to drivers, particularly of automatic vehicles, needs further study. Further work on the interaction between driving style, speed limit and street length should be undertaken to establish whether different instructions should be given according to these variables.

Likely community acceptance

Given that reducing speeding, lower speed limits and modifying driving style can improve fuel economy and other environmental outcomes in addition to improving safety, there is a need to assess another aspect of implementation: the extent to which drivers are motivated by fuel costs and environmental effects.

Community attitude surveys suggest that there will be greater support for measures that aim to improve fuel economy than for those measures that attempt to reduce vehicle travel. In addition, reducing fuel consumption rate without requiring a change in vehicle choice may be more acceptable and more easily implemented in the short-term. Programs such as these that result in reductions in fuel consumption in addition to safety are more likely to be implemented because the benefits (in terms of fuel cost savings) flow directly to the vehicle owner.

Measuring the safety benefits

The case study found that the fuel consumption rate of crash-involved vehicles was higher than that of vehicles not involved in crashes and demonstrated the feasibility of this method. It also showed that while fuel consumption may be easier to measure than safety levels (crash costs), data manipulation and quality control may be time-consuming. The analytical approach is likely to be simpler and more likely to show reliable results if the fleet chosen has well-maintained fuel and crash databases. To show significant effects, the fleet needs to be reasonably large (about 500 vehicles). Analyses with smaller fleets could be undertaken over a longer period but if the period becomes too long, then vehicle and employee turnover may complicate the analyses.

Comparisons before and after training in driving to reduce fuel consumption and analytical studies based on fleet data are recommended as measures of the safety effects of fuel-efficient driving. Studies of the effects of instructions in driving style have the potential to provide useful information about the best ways in which to bring about fuel-efficient driving.

Sponsoring organisation:  Australian Transport Safety Bureau