Interactions between environmental and safety performance in vehicle design

One potential interaction between environmental and safety goals in transport is found within the vehicle fleet where fuel economy and safety impose conflicting requirements on vehicle design. Larger and heavier vehicles have a better secondary safety performance during a crash. On the other hand, they are associated with higher levels of fuel consumption and emissions. This issue has generated debate amongst researchers and policy makers when formulating policies to improve the environmental performance of the road transport system. An extensive review of literature reveals that arguments has often been based on either little research evidence, or research that has inadequacies in the applied methodologies. This research investigates the safety consequences of changes in vehicles mass within the vehicle fleet aimed at increasing fleet fuel economy. The partial effects of mass on fuel consumption rate and secondary safety performance were estimated using a cross-sectional analysis of mass within the British passenger car fleet. Estimation results confirmed that fuel consumption increases as mass increases and were different for different fuel and transmission types. It was shown that vehicle mass has both protective and aggressive safety effects where vehicle size only tends to have protective effects; these were estimated using a novel methodology based on a detailed analysis of two-car crashes. The estimated relationships were used to investigate partial safety and environmental effects of changes in mass distribution within the fleet using an introduced incremental approach. Results generally showed that the relationship between fuel economy and safety performance in vehicle design depends on the characteristics of the vehicle fleet, and in particular, mass distribution. It was shown that an informed change in the mass distribution not only imposes no trade-off between the fuel economy and safety goals, but also could lead to a desirable outcome in both aspects.