IMPACT OF DIFFERENTIAL SPEED LIMITS ON THE SPEED OF TRAFFIC AND THE RATE OF ACCIDENTS

After the enactment of the Surface Transportation and Uniform Relocation Assistance Act in 1987, several states changed the speed limit on rural Interstate highways from 55 to 65 mph. Some of these states have restricted truck speeds by imposing differential speed limits (DSLs). As a result, the maximum speed limit for trucks is 55 mph and that for passenger cars is 65 mph. The objective was to reduce the impact of the increased speed limit on accidents involving trucks. However, the extent to which this strategy has been successful in achieving the objective has not been documented by field data. The nature and extent of the effects of DSLs on vehicle speeds and accident characteristics were assessed. Speed and accident data at study sites in California, Michigan, Maryland, Virginia, and West Virginia were used. Data from Interstates 64, 77, and 81 that traverse Virginia and West Virginia were used for a direct comparison of the DSL. Statistical analysis of the data indicated that, in states where the DSL was imposed (65 mph for nontrucks and 55 mph for trucks), the mean speeds of passenger cars or vehicles other than trucks increased only from 1 to about 4 mph in response to a 10-mph increase in the speed limit. However, there was no significant increase in the mean speed of trucks. Also, following the increase of the speed limit to 65 mph for vehicles other than trucks, speed fluctuations within the traffic stream decreased. On the other hand, speed variances for all vehicles were still higher on Virginia highways with DSL (65/55 mph) compared with those for similar highways in West Virginia operating under 65/65 mph. There is no evidence that the increase in the maximum speed limit to 65 mph for passenger vehicles on the rural Interstate systems in the states studied has directly resulted in a significant increase in fatal, injury, or overall accident rates.

• Record URL:
  • http://onlinepubs.trb.org/Onlinepubs/trr/1992/1375/1375-007.pdf
• Record URL:
  • https://scholar.google.com/scholar_lookup?title=IMPACT+OF+DIFFERENTIAL+SPEED+LIMITS+ON+THE+SPEED+OF+TRAFFIC+AND+THE+RATE+OF+ACCIDENTS&author=N.+Garber&author=R.+Gadiraju&publication_year=1992
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• Supplemental Notes:
  • This paper appears in Transportation Research Record No. 1375, Safety Research: Enforcement, Speed, Older Drivers, and Pedestrians. Distribution, posting, or copying of this PDF is strictly prohibited without written permission of the Transportation Research Board of the National Academy of Sciences. Unless otherwise indicated, all materials in this PDF are copyrighted by the National Academy of Sciences. Copyright © National Academy of Sciences. All rights reserved
• Authors:
  • Garber, Nicholas J
  • Gadiraju, Ravi
• Publication Date: 1992

Language

• English

Media Info

• Features: References; Tables;
• Pagination: p. 44-52
• Monograph Title: Safety research: enforcement, speed, older drivers, and pedestrians
• Serial:
  • Transportation Research Record
  • Issue Number: 1375
  • Publisher: Transportation Research Board
  • ISSN: 0361-1981

Subject/Index Terms

• TRT Terms: 55 mph speed limit; 65 mph speed limit; Crash rates; Impact studies; Interstate highways; Passenger cars; Rural highways; Speed limits; Statistical analysis; Traffic speed; Trucks
• Uncontrolled Terms: Differential speed
• Geographic Terms: California; Maryland; Michigan; Virginia; West Virginia
• Subject Areas: Data and Information Technology; Highways; Motor Carriers; Operations and Traffic Management; Safety and Human Factors; I73: Traffic Control; I81: Accident Statistics;

Filing Info

• Accession Number: 00627211
• Record Type: Publication
• ISBN: 0309054184
• Files: TRIS, TRB, ATRI
• Created Date: Apr 1 1993 12:00AM