Dissertation Title： "The Environmental and Safety Risks of Sport-Utility Vehicles, Vans, and Pickup Trucks"The composition of the passenger vehicle fleet in the US has been undergoing a major change. Sport-utility vehicles, vans, and pickup trucks, collectively known as light-duty trucks (LDTs), have become very popular. Whereas LDT sales comprised one-fifth of the market in 1975, they now account for about half. Concern has grown that this trend may have adverse impacts on public health. This thesis presents three studies that examine the environmental and safety implications of cars and LDTs.

The first study compares the environmental damages from passenger vehicles. It analyzes air pollutant emissions from model year 2001 cars, small/medium-sized LDTs, and large LDTs. Emissions from gasoline production and vehicle use are estimated. The damages considered include health effects associated with particulate matter and ozone and the impacts of greenhouse gas emissions. These damages are valued in economic terms. Cars are associated with damages totaling $2,600; small/medium LDTs and large LDTs cause about one-third and three-quarters more damage, respectively.

The second study examines the traffic safety risks in two-vehicle crashes involving cars and/or LDTs. Logistic regression methods and real-world crash data from the Crashworthiness Data System are used to compare the crashworthiness (self-protection) and aggressivity (risk to others) of cars, SUVs, vans, and pickups. A unique feature of the study is that it controls for the joint effects of vehicle mass and crash severity. Compared to cars, pickups provide greater crashworthiness but are more aggressive; effects associated with SUVs and vans were less pronounced. Vehicle characteristics besides mass have an important influence on safety risks.

The third study characterizes trends in the distribution of vehicle mass among the on-road fleet of cars and LDTs. Large disparities in vehicle mass appear to increase net safety risks in two-vehicle crashes. Publicly available data are used to develop a simple model of the passenger vehicle fleet from 1975 to 2001. The variance in mass declined substantially from 1975 to 1996, possibly due to the effects of fuel economy standards. Since 1996, however, variance has increased and is likely to continue an upward trend; this is likely due to the growth in popularity of LDTs.