sitemap Effects of Speed on Pedestrian Fatality Rates

Effects of Vehicle Speed on Pedestrian Fatalities

Newton's laws dictate that a doubling in vehicle speed results in a stopping distance four times as long and four times as much kinetic energy absorbed during an impact. Driver response times further increase stopping distances. As a result, a small increase in roadway traffic speeds results in a disproportionately large increase in pedestrian fatalities. This relatonship is illustrated in the references listed below.

From Embarcadero Road Traffic Calming Project, Preliminary Report, Patrick Siegman Siegman & Associates, Town & Transportation Planning 260 Palo Alto AvenuePalo Alto CA 94301, siegman@sirius.com, as posted on Pednet:

For both stopping distances and the severity of crashes, speed matters. Travelling at 40 mph, the average driver who sights a pedestrian in the road 100 feet ahead will still be travelling 38 mph on impact: driving at 25 mph, the driver will have stopped before the pedestrian is struck.

Source: McLean AJ, Anderson RWG, Farmer MJB, Lee BH, Brooks CG. Vehicle Speeds and the Incidence of Fatal Pedestrian Collisions - Volume 1. Federal Office of Road Safety, Australia. See also Traditional Neighborhood Development Street Design Guidelines. Transportation Planning Council Committee 5P-8, Institute of Transportation Engineers. Washington D.C., 1997, p. 15-16.

 

The following table shows how, when a pedestrian is struck, the likelihood of death increases faster than the percentage increase in vehicle speed, in a nonlinear fashion:

Relationship of Vehicle Speed to Odds of Pedestrian Death in Collision

Vehicle Speed

Odds of Pedestrian Death, Source 1

Odds of Pedestrian Death, Source 2

20 mph

5%

5%

30 mph

45%

37%

40 mph

85%

83%

[Source 1: Killing Speed and Saving Lives, UK Dept. of Transportation, London, England. See also Limpert, Rudolph. Motor Vehicle Accident Reconstruction and Cause Analysis. Fourth Edition. Charlottesville, VA. The Michie Company, 1994, p. 663.]

[Source 2: Vehicle Speeds and the Incidence of Fatal Pedestrian Collisions prepared by the Austrailian Federal Office of Road Safety, Report CR 146, October 1994, by McLean AJ,Anderson RW, Farmer MJB, Lee BH, Brooks CG.]

The implications of this relationship on the impact of speed limits and law enformcement policy is explored in Reference [2] above:

Abstract:

The aim of this study by the NHMRC Road Accident Research Unit was to estimate the likely effect on pedestrian fatalities of a reduction in vehicle travelling speed. Results were based on detailed investigations of 176 fatal pedestrian collisions in the Adelaide area between 1983 and 1991. Estimates were developed for a range of speed reduction scenarios. The study found that a reduction of 5 km/h in the Adelaide area could be expected to result in a reduction of 30% of the incidence of fatal pedestrian collisions. Under this scenario 10% of collisions would have been avoided altogether. Volume I of this report contains detailed findings for each speed reduction scenario along with a description of the method used and supporting references. Volume II contains the details of all 176 cases.

....

In Zurich, the urban area speed limit was lowered from 60 to 50 km/h [37 to 31 mph] in 1980 in response to a reduction in the open road speed limit (following political pressure from the Green movement to reduce pollution levels from cars to save the forests). In the year after the change in the urban speed limit there was a reduction of 16 percent in pedestrian accidents and a reduction of 25 percent in pedestrian fatalities (Walz et al, 1983). (The authors of this study observed that, because of those who "don't believe in the influence of driving speed on impact speed" or who "just don't care at all", "it must be proven in every country that the laws of Isaac Newton are true".) [page 41]