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Status Report, Vol. 35, No. 5 | May 13, 2000 Subscribe

Vehicle speed and pedestrian age determine crash outcomes

Regardless of age, pedestrians involved in crashes are more likely to be killed as vehicle speeds increase. In crashes at any speed, older pedestrians are more likely to die than younger ones. These are the two main findings of a report on pedestrian injuries recently prepared by the Preusser Research Group for the National Highway Traffic Safety Administration.

Analyzing crashes across the country, researchers found that fewer than 2 percent of struck pedestrians died in crashes that occurred where posted speed limits were slower than 25 mph. Where speed limits were 50 mph or higher, more than 22 percent of struck pedestrians died. The correlation was much the same when researchers looked at vehicle travel speeds — crash data from Florida show the proportion of serious injuries and fatalities among pedestrians went up along with vehicle speeds, as estimated by police investigating the crashes.

"Pedestrians age 65 and older are more than 5 times as likely to die in crashes than pedestrians age 14 or less, and the likelihood of death increases steadily for ages in between," the authors observe. Younger pedestrians generally have a greater chance of withstanding impacts unharmed, while elderly pedestrians are more susceptible to serious injury or death.

These findings aren't surprising given the physical disproportions between cars and pedestrians. Anyone who has walked along a street and felt the rush of cars whizzing by has a visceral sense of the danger. Car occupants have several tons of metal surrounding them, and safety belts and airbags buffer them from crash forces. In contrast, pedestrians are unprotected and weigh a small fraction of any car that strikes them, so they're extremely vulnerable.

The logical solution is to limit vehicle speeds in areas where pedestrians are present, because speed determines impact severity. With every small increase in speed, pedestrian deaths go up even faster. The authors cite research concluding that about 5 percent of pedestrians hit by a vehicle traveling 20 mph will die. The fatality rate jumps to 40 percent for cars traveling 30 mph, 80 percent for cars going 40 mph, and 100 percent for cars going 50 mph or faster.

Lowering speed limits alone can bring small improvements. In most studies, the authors report, actual travel speeds dropped by a quarter or less of the posted speed limit reductions. Effective enforcement is more critical. Institute senior vice president Allan Williams explains that "for enforcement to deter speeding, drivers must believe the enforcement efforts are being made in the specific locations where they drive and at the times when they drive there. Even the presence of enforcement isn't enough. The consequences of getting stopped for speeding have to be meaningful enough to keep drivers from knowingly taking the risk."

It's impossible to put a police officer on every street, so cameras are a practical means of increasing the perception of enforcement. Red-light cameras already have won favor in jurisdictions around the country. Speed cameras aren't as popular, but they're equally effective deterrents (see "Officials nationwide give a green light to automated enforcement," March 11, 2000).

On the other hand, the designs of roadways often encourage drivers to go faster than the posted speed limits. Travel speeds can be restricted by introducing road treatments such as humps, rumble strips, paving stones or other rough surfaces instead of asphalt, and by road narrowing (see Status Report special issue: urban crashes, May 2, 1998). With the right planning, modern roundabouts and other road treatments designed to reduce speeds can serve pedestrian safety as well as ease other traffic problems.

To make roads safer for pedestrians, engineers also should place crosswalks away from stop lines and merge areas. Traffic signal intervals should be set to allow pedestrians enough time to cross. And installing sidewalks or better lighting can prevent unnecessary collisions.

Percent of struck pedestrians with fatal injuries, by pedestrian age and vehicle speed

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