In May 1987, a 65-mph speed limit was posted on rural interstate highways in Illinois. The effect of the change in vehicle speeds on the incidence of accidents is assessed for the first year. The method consisted of using 5 years of data collected before the new speed limit and subjecting these data to linear regression to project the number of accidents had there been no change in the posted speed limit. The projected number of accidents of each type was then compared with the reported numbers for the period of the assessment. Average speeds of passenger vehicles on the rural interstates increased from 59.8 Mph during the preceding year to 61.8 mph during the initial 12 months of the increased speed limit. The number of fatal accidents (expected versus reported) increased on each of the three different types of highways (15.2% on rural interstates, 20.3% on urban interstates, and 2.9% on the primary system of highways). Most of the increase in fatal accidents on the rural interstates may be attributed to the increase in fatal pedestrian accidents and fatal accidents involving drinking and driving. Results indicate that the higher posted speed limit in Illinois did not have a clearly noticeable or an obviously adverse effect on fatal accidents during its first year. This paper appears in Transportation Research Record No. 1281, Human Factors and Safety Research Related to Highway Design and Operation 1990.
Samenvatting