bear increased attention. As a possible adjunct to such a system, automatic braking activated by
the same radar signal could reduce crash severity.
Another interesting design solution proposed by the Swiss involves building the lightweight
vehicle with an extremely stiff “impact belt” around the exterior of the vehicle.^91 The idea here is
that, in case of a collision with a heavier vehicle, the rigidity of the vehicle shell would cause the
front of the heavier vehicle to deform substantially. In essence, the lighter vehicle uses the crush
space of the heavier vehicle as its own crush space, and the heavier vehicle absorbs most of the
kinetic energy released in the crash.^92 This design also includes very strong and stiff side beams
that prevent intrusion of the car door into the passenger compartment during a side impact,
avoiding the main cause of severe injuries during this type of collision.^93
This type of design demands that restraint systems and interior padding bear much of the task
of dealing with deceleration, especially in accidents where the vehicle strikes largely immovable
objects. Although the structure does not eliminate crush space--it does deform in a crash--it
reduces crush space and will increase the deceleration forces on passengers in many crashes.^94 It
also demands that heavy cars be built with lower rigidity in their front and rear structures, so they
can absorb most of the kinetic energy of crashes with lighter vehicles.^95 Another concern of this
type of design is its potential to increase the aggressivity of light cars in collisions into the sides of
other vehicles. Of particular concern is the incidence of vehicle-to-vehicle crashes where both
vehicles are of this design. In such collisions, deceleration forces on the passengers would be
substantially higher than in collisions between vehicles of more conventional design. Thus far, the
Swiss have focused this design on very small vehicles, and this maybe where the design makes the
most sense--when there simply is no room for much crush space. In OTA’s view, this type of
design, if used in standard-size vehicles, would be likely to create more problems than it
eliminates.
Improvements in restraint systems will increase safety in all vehicles. In particular, crash
sensors with very fast response times allow more time for deploying airbags and thus allow
deployment to be less aggressive. This might mitigate some of the injuries that rapidly deploying
airbags have been known to cause. Also, so-called “smart” restraint systems potentially may
deploy the air bag differently depending on crash severity, position of the vehicle occupant, and
characteristics of the occupant (e.g., size, sex, age), yielding greater protection.Additional IssuesOTA’s workshop on the safety of lightweight vehicles identified numerous additional issues.
First, regardless of whether or not lightweight vehicles adopt any kind of “impact belt” design,(^91) R. Kaeser et al., "Collision Safety of a Hard-Shell Low-Mass Vehicle,” Accident Analysis and Prevention, vol. 26, No. 3, 1994, pp. 399-406.
(^92) Ibid.
(^93) Ibid. Although passengers are likely to strike the door whether or not the doors are pushed in or the entire vehicle is pushed sideways as a unit,
the impact forces are far lower in the latter case. 94
In a very small vehicle that would not have much crush space to begin with, this type of design has fewer tradeoffs. However, the vehicles we
are considering here are lighter but not smaller than conventional vehicles. 95
Ibid.