words, analysts often have a hard time determining whether it is weight or size (or even some
other measure) that is the primary determinant of safety, because large cars are usually heavy cars,
and small cars are usually light. One analysis concluded that weight was the more important factor
in vehicle safety.^83 This conclusion has been disputed by others, who claim that extremely
lightweight vehicles can be made as safe as heavier ones.
The Role of Weight in Accident Prevention and Crashworthiness
An examination of the role that vehicles play in maintaining occupant safety can be instructive
in determining the potential impact of sharp weight reductions. The vehicle must do the following:
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5.Aid the driver in keeping the vehicle on the roadway.If the vehicle leaves the roadway, avoid a rollover.In a crash, absorb crash forces in such a way that no intrusion of the passenger compartment
occurs.Also, control the deceleration of the vehicle so that it occurs in as uniform a way as possible,
over as long a crush distance^84 as possible.Finally, prevent the passenger from crashing against interior surfaces and/or minimize damage if
he does, prevent ejection of the passenger, and control the way deceleration forces affect the
passenger.Weight plays a different role in each of these vehicle tasks. In (l), weight may be protective in
keeping vehicles from being adversely affected by crosswinds, but directional stability and
handling are affected far more by wheelbase, suspension, and steering system design, tire design
and maintenance, and other nonweight-related factors.
In (2), rollover can be weight-related because in lightweight cars, the payload will have a
greater effect on the height of the center-of-gravity than it will in heavier cars. This effect maybe
positive or negative depending on vehicle design, and specifically on the location of the payload
vis-à-vis the location of the empty vehicle’s center-of-gravity. However, rollover propensity is
primarily a function of wheelbase, track width, suspension design, and overall vehicle design; a
small increase in track width can compensate for any increase in rollover propensity that might
occur from “lightweighting” a vehicle.
In (3) and (4), the role of weight is complex. The ability of the vehicle structure to control
crash forces and prevent penetration of the passenger space for a given set of forces on the
vehicle is dependent on vehicle design and the strength, rigidity, and deformation characteristics
of the structure--not specifically on weight. Thus, it would appear at first glance that substitution