Effects of Raising and Lowering Speed Limits

(Part of the Reasonable Drivers Unanimous site)

Final Report

Report No. FHWA-RD-92-084                                      October 1992

U.S. Department of Transportation      Research, Development, and Technology
Federal Highway Administration         Turner-Fairbank Highway Research Center
                                       6300 Georgetown Pike
                                       McLean, Virginia 22101-2296

Type of report and dates covered:
Final, October 1985 - June 1992
The objectives of this research was to determine the effects of raising and lowering posted speed limits on driver behavior and accidents for non-limited access rural and urban highways. Speed and accident data were collected in 22 States at 100 sites before and after speed limits were altered. Before and after data were also collected simultaneously at comparison sites where speed limits were not changed to control for the time trends. Repeated measurements were made at 14 sites to examine short - and long-term effects of speed limit changes.

The results of the study indicated that lowering posted speed limits by as much as 20 mi/h (32 km/h), or raising speed limits by as much as 15 mi/h (24 km/h) had little effect on motorist' speed. The majority of motorist did not drive 5 mi/h (8 km/h) above the posted speed limits when speed limits were raised, nor did they reduce their speed by 5 or 10 mi/h (8 or 16 km/h) when speed limits are lowered. Data collected at the study sites indicated that the majority of speed limits are posed below the average speed of traffic. Lowering speed limits below the 50th percentile does not reduce accidents, but does significantly increase driver violations of the speed limit. Conversely, raising the posted speed limits did not increase speeds or accidents.

Performing Organization Name and Address:
Martin R. Parker & Associates, Inc.
38549 Laurenwood Drive
Wayne, Michigan 48184-1073
Sponsoring Agency Name and Address:
Office of Safety and Traffic Operations R&D
Federal Highway Administration
6300 Georgetown Pike
McLean, Virginia 22101-2296
Contracting Officer's Technical Representative (COTR):
Howard H. Bissell, HSR-30 and Davey L. Warren, HSR-10.
Contract or Grant Number:
HTMLised by:
Kevin Atkinson, kevinatk@home.com

Under Contruction. Figures and the rest of the text to be added soon.

Table of Contents

The entire report is 84 pages long. You can try calling the National Technical Information Service (general info 703-487-4770, sales 703-487-4650) and asking for this report. Even with the report number they won't be able to find it. It's being buried since it says things that certain organizations (both governmental and private) don't want to be made public. However, NMA is selling this report for $15 plus $4 shipping and handaling. They can be contacted at 608/849-6000; nma@motorists.com ; or 6678 Pertzborn Road, Dane, Wisconsin 53529.

This page is part of a larger Reasonable Drivers Unanimous site. Be sure to check the rest of my site out if this is your first time visiting. You won't regret it!

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