The Effect of Heavy Vehicles on Traffic Safety

Summary of working paper 9302
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The current system does not penalize drivers of heavy vehicles at all for causing disproportionate deaths and damage.

In recent years Americans have been buying increasingly heavy vehicles, creating what NBER Research Associate Michelle J. White calls an "arms race" on America's roads. Between 1980 and 1998, sales of heavier vehicles, primarily light trucks, SUVs, and vans, more than tripled, from approximately 2 million to 7 million per year. As a proportion of all registered vehicles, their numbers increased from 21 percent to 37percent.

In The "Arms Race" on American Roads: The Effect of Heavy Vehicles on Traffic Safety and the Failure of Liability Rules (NBER Working Paper No. 9302), White divides the cost of accidents into internal benefits versus external costs. She finds that while drivers view large vehicles as a way to better protect their occupants (internal benefits), in the event of an accident those same larger vehicles pose a greater danger to occupants of smaller vehicles and to pedestrians and bicyclists (external costs). When drivers replace cars with light trucks, 3700 additional crashes per year involving fatalities of smaller vehicle occupants, pedestrians, and bicyclists occur, while only 1400 crashes involving fatalities of light truck occupants are avoided. This produces a ratio of negative external effects to positive internal effects of 2.5 to 1.

White argues that none of the existing traffic laws or highway safety institutions force drivers of heavy vehicles to be held responsible for the negative external effects of their ownership. Tort liability, for example, instead might fall more heavily on owners of heavy than light vehicles. That would both cause drivers of heavy vehicles to use additional care to avoid accidents and discourage them from driving heavy vehicles in the first place. However, liability for automobile damage is generally based only on negligence, irrespective of vehicle weight class. In addition, many states use no-fault systems rather than negligence rules to determine liability. The current system does not penalize drivers of heavy vehicles at all for causing disproportionate deaths and damage.

The flaw in the tort liability system is paralleled in liability insurance premiums. Drivers of heavier vehicles do not necessarily pay higher rates than drivers of light vehicles. A similar flaw is found in state traffic rules, which apply the same standard of driving behavior and apply the same penalties on all drivers, regardless of the potential of drivers of heavier vehicles to cause more serious damage and injury.

White describes reforms that would mitigate the negative effects of driving heavier vehicles, including lower speed limits and more stringent driving rules for heavier vehicles, requiring that all vehicle owners in all states buy liability insurance, raising the minimum required levels of liability insurance coverage, and replacing no-fault liability systems for motor vehicle accidents with fault-based systems.

-- Les Picker