Safety Of Lightweight Vehicles

Several of the advanced vehicles examined by OTA will be extremely light. For example, one of the 2015 advanced conventional vehicles weighs less than 2,000 pounds. An examination of the basic physics of vehicle accidents and the large U.S. database on fatal and injury-causing accidents indicates that a substantial “down weighting” of the light-duty fleet will create some significant safety concerns, especially during the transition period when new, lighter vehicles mix with older, heavier ones. Any adverse safety impacts, however, are unlikely to be nearly so severe as those that occurred as a result of changes in the size and weight composition of the new car fleet in 1970 to 1982.67 The National Highway Traffic Safety Administration concluded that those changes “resulted in (net) increases of nearly 2,000 fatalities and 20,000 serious injuries per year. ” Many of those adverse impacts occurred because vehicles changed in size as well as weight, however, yielding reduced crush space, reduced track width and wheelbase (which increased the incidence of vehicle rollovers), and so forth. Reducing weight while maintaining vehicle size and structural integrity should have lower impacts. The major areas of concern about vehicle “light weighting” are the following:

Passengers in lighter vehicles tend to fare much worse than the passengers in heavier ones in collisions between vehicles of unequal weight, because heavy vehicles transfer more momentum to lighter cars than vice-versa. During the long transition period when older, heavier vehicles would remain in the fleet, lightweight vehicles might fare poorly. Moreover, if the large numbers of light trucks in the fleet do not reduce their weight proportionately, the weight distribution of the fleet could become wider, which would cause adverse impacts on safety.

Vehicle designers must balance the need to protect passengers from deceleration forces (requiring crush zones of lower stiffness), and the need to prevent passenger compartment intrusion (requiring high strength/high stiffness structure surrounding the passengers). 68 Lighter vehicles will have lower crash energy in barrier crashes or crashes into vehicles of similar weight, so they will require a softer front structure than a heavier vehicle to obtain the same degree of crush (and same protection against deceleration forces) in otherwise similar crashes (e.g., barrier crashes at the same velocity). Designing large, lightweight vehicles with soft structures that have acceptable ride and handling characteristics (structural stiffness is desirable for obtaining good ride and handling characteristics) and are protective against passenger compartment intrusion may be a challenge to vehicle designers. Additionally, the differential needs for stiffness among lighter and heavier vehicles may cause compatibility problems in multi-vehicle crashes.

In collisions with roadside obstacles, lighter vehicles have less chance than a heavier vehicle of deforming the obstacle or even running through it, both of which would decrease deceleration forces on the occupants. Also, a substantial decrease in average vehicle weight might cause compatibility problems with current designs of safety barriers and breakaway roadside devices (e.g., light poles), which are designed for a heavier fleet.

If weight reductions are achieved by shifting to new materials, vehicle designers may need considerable time to regain the level of modelling expertise currently available in designing steel vehicles for maximum safety.

There exist several safety design improvements that could mitigate any adverse effects caused by large fleetwide weight reductions—though, of course, such measures could improve fleet safety at any weight. Examples include external air bags deployed by radar sensing of impending accidents; accident avoidance technology such as automatic braking; and improvements in vehicle restraint systems (including faster acting sensors and “smart” airbags that can adjust to accident conditions and occupant characteristics). The latter would greatly benefit from further biomechanical research to improve our understanding of accident injury mechanisms.

Large fleet weight reductions also will intensify the need for the National Highway Traffic Safety Administration to examine carefully its array of crash tests for vehicles, to ensure that these tests provide incentives to maximize vehicle-to-vehicle compatibility in crashes.

A Note About Costs And Prices

The price of advanced technologies is a controversial aspect of the continuing debate over the merits of several government actions promoting such technologies. These actions range from the alternative fuel vehicle requirements of the federal Energy Policy Act of 199269 to California’s ZEV requirements to federal funding (in concert with industry) of PNGV. OTA’s estimates of retail price differentials for advanced conventional vehicles are somewhat below industry estimates, while estimates for hybrid, fuel cell, and electric vehicles seem to be above some others prepared by advocacy groups. Part of the difference between OTA’s estimates and others undoubtedly reflects the substantial uncertainty that underlies any efforts to predict future prices of new technologies. Other differences arise from the following sources

· OTA’s relatively low incremental prices for advanced conventional vehicles rest partly on our assumption that the advanced technologies are competing with baseline technologies that are new models with newly designed assembly lines; the baseline vehicles are not simply continued production of an existing technology whose investment costs may have been fully amortized.

· OTA’s relatively high prices for hybrid, fuel cell, and electric vehicles reflect in part OTA’s assumption that these vehicles are competitive in performance with the baseline, conventional vehicles; other estimates often reflect lesser performing vehicles, which our analysis concludes would be considerably less expensive.

· Another source of price differences is OTA’s assumption that vehicle prices must costs and manufacturer/dealer profits beyond the manufacturing costs for vehicle price estimates do not reflect these additional costs.