Evaluation of the 55 MPH Speed Limit

Abstract

Speed limits have been established for the good of the motoring public, primarily for purposes of safety. A study has shown that by reducing the number of violators on freeways, the resulting more uniform speeds contribute to improved capacity and safety (22). The effectiveness of a speed limit on a facility depends on the degree of enforcement and public support (3,4). The public will support and obey speed limits that are safe and reasonable; however, speed limits that are illogically restrictive cannot be enforced except by tremendous effort and expense, and then usually not for 1 ong (3). It is the duty of traffic engineers to establish speed limits by careful investigation and evaluation. The most commonly used method of establishing speed limits is to take the 85th percentile of the observed speeds (32,26). J. C. Oppenlander suggests another method of establishing the best operating speed by optimizing the three resources expended in highway transportation: the economics of vehicle operation, the value of time, and the safety of travel (33). Driver Characteristics The speed a driver chooses is dependent upon his desires and environment; therefore, speed control is difficult because of variations in the driving behavior of individuals (3,22).

Evaluating the Impacts of Freeway Speed Limit Increases on Various Speed Measures: Comparisons Between Spot-Speed, Permanent Traffic Recorder, and Probe Vehicle Data

“…Additionally, the entire speed distribution is examined along with variabilities in speed instead of just the mean speed. Several studies utilize aggregate data to compare before-after speed metrics using ordinary least squares (OLS) regression techniques (5,34,35,40,41) and others use analysis of variance (ANOVA) and t-tests (36,37,42). Testing only the mean speed (using linear regression or a typical t-test or ANOVA) cannot indicate whether the changes or differences observed are the result of slower traffic driving faster now, or faster traffic driving much faster, or both.…”

Analysis of Rural Interstate Fatality Rates in Consideration of Recent Increases in Maximum Statutory Speed Limits

“…In response to the NMSL in 1974, several research studies were conducted to evaluate its effects. One 1975 study in Indiana saw fatalities on rural highways decrease by 67%, personal injury crashes decrease by 32%, and property damage only crashes decrease by 13% in the first half of 1974 when compared with the same period of the three previous years ( 1 ). Another study in Michigan over the same time period saw a 20% decrease in total crashes and injury crashes and a 17% decrease in fatal crashes on freeways ( 2 ).…”

“…Maximum statutory speed limits have been an issue of longstanding debate. Following the introduction of the National Maximum Speed Limit (NMSL) in 1974, a series of longitudinal studies showed significant decreases in traffic fatalities ( 1 , 2 ). In 1987, states were given the authority to increase limits on rural interstates to 65 mph, spurring a series of additional research studies that showed marked increases in fatalities subsequent to these speed limit increases ( 3 , 4 ).…”