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Analysis of the Relationship Between Vehicle Weight/Size and Safety, and Implications for Federal Fuel Economy Regulation

Description: This report analyzes the relationship between vehicle weight, size (wheelbase, track width, and their product, footprint), and safety, for individual vehicle makes and models. Vehicle weight and footprint are correlated with a correlation coefficient (R{sup 2}) of about 0.62. The relationship is stronger for cars (0.69) than for light trucks (0.42); light trucks include minivans, fullsize vans, truck-based SUVs, crossover SUVs, and pickup trucks. The correlation between wheelbase and track width, the components of footprint, is about 0.61 for all light vehicles, 0.62 for cars and 0.48 for light trucks. However, the footprint data used in this analysis does not vary for different versions of the same vehicle model, as curb weight does; the analysis could be improved with more precise data on footprint for different versions of the same vehicle model. Although US fatality risk to drivers (driver fatalities per million registered vehicles) decreases as vehicle footprint increases, there is very little correlation either for all light vehicles (0.01), or cars (0.07) or trucks (0.11). The correlation between footprint and fatality risks cars impose on drivers of other vehicles is also very low (0.01); for trucks the correlation is higher (0.30), with risk to others increasing as truck footprint increases. Fatality risks reported here do not account for differences in annual miles driven, driver age or gender, or crash location by vehicle type or model. It is difficult to account for these factors using data on national fatal crashes because the number of vehicles registered to, for instance, young males in urban areas is not readily available by vehicle type or model. State data on all police-reported crashes can be used to estimate casualty risks that account for miles driven, driver age and gender, and crash location. The number of vehicles involved in a crash can act as a ...
Date: March 2, 2010
Creator: Wenzel, Thomas P.
Partner: UNT Libraries Government Documents Department

Comments on the Joint Proposed Rulemaking to Establish Light-Duty Vehicle Greenhouse Gas Emission Standards and Corporate Average Fuel Economy Standards

Description: I appreciate the opportunity to provide comments on the joint rulemaking to establish greenhouse gas emission and fuel economy standards for light-duty vehicles. My comments are directed at the choice of vehicle footprint as the attribute by which to vary fuel economy and greenhouse gas emission standards, in the interest of protecting vehicle occupants from death or serious injury. I have made several of these points before when commenting on previous NHTSA rulemakings regarding CAFE standards and safety. The comments today are mine alone, and do not necessarily represent the views of the US Department of Energy, Lawrence Berkeley National Laboratory, or the University of California. My comments can be summarized as follows: (1) My updated analysis of casualty risk finds that, after accounting for drivers and crash location, there is a wide range in casualty risk for vehicles with the same weight or footprint. This suggests that reducing vehicle weight or footprint will not necessarily result in increased fatalities or serious injuries. (2) Indeed, the recent safety record of crossover SUVs indicates that weight reduction in this class of vehicles resulted in a reduction in fatality risks. (3) Computer crash simulations can pinpoint the effect of specific design changes on vehicle safety; these analyses are preferable to regression analyses, which rely on historical vehicle designs, and cannot fully isolate the effect of specific design changes, such as weight reduction, on crash outcomes. (4) There is evidence that automakers planned to build more large light trucks in response to the footprint-based light truck CAFE standards. Such an increase in the number of large light trucks on the road may decrease, rather than increase, overall safety.
Date: October 27, 2009
Creator: Wenzel, Thomas P
Partner: UNT Libraries Government Documents Department

Safer Vehicles for People and the Planet

Description: Motor vehicles contribute to climate change and petroleum dependence. Improving their fuel economy by making them lighter need not compromise safety. The cars and trucks plying America's roads and highways generate roughly 20 percent of the nation's total emissions of carbon dioxide, a pollutant that is, of course, of increasing concern because of its influence on climate. Motor vehicles also account for most of our country's dependence on imported petroleum, the price of which has recently skyrocketed to near-record levels. So policymakers would welcome the many benefits that would accrue from lessening the amount of fuel consumed in this way. Yet lawmakers have not significantly tightened new vehicle fuel-economy standards since they were first enacted three decades ago. Since then, manufacturers have, for the most part, used advances in automotive technology, ones that could have diminished fuel consumption, to boost performance and increase vehicle weight. In addition, the growth in popularity of pickups, sport utility vehicles (SUVs) and minivans--and the large amounts of gas they typically guzzle--has resulted in the average vehicle using the same amount of fuel per mile as it did 20 years ago. One of the historical impediments to imposing tougher fuel-economy standards has been the long-standing worry that reducing the mass of a car or truck to help meet these requirements would make it more dangerous to its occupants in a crash. People often justify this concern in terms of 'simple physics', noting, for example, that, all else being equal, in a head-on collision, the lighter vehicle is the more strongly decelerated, an argument that continues to sway regulators, legislators and many in the general public. We have spent the past several years examining the research underlying this position--and some recent work challenging it. We have also conducted our own analyses and come to the conclusion ...
Date: March 1, 2008
Creator: Wenzel, Thomas P; Wenzel, Thomas P & Ross, Marc
Partner: UNT Libraries Government Documents Department

Safer Vehicles for People and the Planet: Letter to the Editor

Description: Letter to the Editors from Leonard Evans, Bloomfield Hills, MI: Single-vehicle crashes, which account for half of occupant fatalities, are not mentioned in 'Safer Vehicles for People and the Planet', by Thomas P. Wenzel and Marc Ross (March-April). Simple physics shows that in such crashes risk declines as vehicle mass increases. The authors write 'driving imported luxury cars carries extremely low risk, for reasons that are not obvious'. The reasons are obvious--the cars are purchased by low-risk drivers. If they swapped vehicles with drivers of sports cars (which have high risk), the risks would stick with the drivers, not the vehicles. The article reflects the American belief that death on our roads can be substantially reduced by making vehicles in which it is safer to crash. From 1979 through 2002, Great Britain, Canada and Australia reduced fatalities by an average of 49 percent, compared with 16 percent in the U.S. Accumulating the differences over this time shows that by merely matching the safety performance of these other countries, about 200,000 fewer Americans would have died. These trends continue. In 2006 the U.S. recorded 42,642 traffic deaths, a modest 22 percent decline from our all-time high. Sweden recorded 445, a reduction of 66 percent from their all-time high. The obsessive focus on vehicles rather than on countermeasures that scientific research shows substantially reduce risk is at the core of our dramatic safety failure. The only way to substantially reduce deaths is to reduce the risk of crashing, not to make it safer to crash. The response from Drs. Wenzel and Ross: Of course Dr. Evans is correct in stating that driver behavior influences crash risk. In our article we made clear that our estimates of risk include how well a vehicle/driver combination avoids a crash, as well as how crash-worthy a ...
Date: May 1, 2008
Creator: Wenzel, Thomas P; Wenzel, Thomas P & Ross, Marc
Partner: UNT Libraries Government Documents Department