EFFECT OF THE 65-MPH SPEED LIMIT ON SPEEDS IN THREE STATES

Following the April 1987 enactment of federal law permitting 65-mph speed limits on rural Interstate highways, 40 states adopted higher speed limits by the middle of 1988. Nondetectable radar was used to measure speeds in three states to evaluate the effect of the 65-mph speed limit on speeds of free-flowing vehicles on Interstate highways during daytime off-peak periods (9:00 a.m. to 4:00 p.m.). In New Mexico, rural and urban speeds were measured at 2-month intervals over a 2-year period after the speed limit was increased in April 1987. In Virginia and Maryland, rural speed data were collected immediately before and after Virginia implemented the 65-mph limit in July 1988 and data collection was repeated at 3-month intervals for 1 year. Two weeks after the 65-mph speed limit began in Virginia, mean and 85th-percentile speeds of cars were higher by almost 3 mph, whereas the speed of tractor-trailers (still limited to 55 mph) was unchanged. The proportion of cars exceeding 70 mph nearly doubled. Speeds of cars and trucks in neighboring Maryland (with 55-mph speed limit) did not increase during the same 2 weeks. A longer-term trend of increasing speed was also found in Virginia. In contrast, car speeds in Maryland showed no upward trend, but tractor-trailer speeds have increased to the same level as in Virginia. In New Mexico, average speeds of passenger cars and light trucks on rural highways increased nearly 3 mph within 9 months of the 65-mph law and have since continued to increase. The proportion exceeding 70 mph grew nearly fivefold for cars and doubled for heavy trucks. Urban highway speeds in New Mexico have shown a slight increase over 27 months, while also exhibiting pronounced seasonal variation.

• Record URL:
  http://onlinepubs.trb.org/Onlinepubs/trr/1990/1281/1281-006.pdf
• Record URL:
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• Supplemental Notes:
  • This paper appears in Transportation Research Record No. 1281, Human Factors and Safety Research Related to Highway Design and Operation. 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
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  Transportation Research Board

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• Authors:
  • Freedman, Mark
  • Esterlitz, Joy R
• Publication Date: 1990

Media Info

• Features: Figures; References; Tables;
• Pagination: p. 52-61
• Monograph Title: HUMAN FACTORS AND SAFETY RESEARCH RELATED TO HIGHWAY DESIGN AND OPERATION 1990
• Serial:
  • Transportation Research Record
  • Issue Number: 1281
  • Publisher: Transportation Research Board
  • ISSN: 0361-1981

Subject/Index Terms

• TRT Terms: 65 mph speed limit; 85th percentile speed; Automobiles; Before and after studies; Data collection; Days; Off peak periods; Rural highways; Speed; Trend (Statistics); Trucks
• Identifier Terms: Interstate Highway System
• Geographic Terms: Maryland; New Mexico; Virginia
• Old TRIS Terms: Off-peak
• Subject Areas: Highways; Motor Carriers; Operations and Traffic Management; Safety and Human Factors; I73: Traffic Control; I83: Accidents and the Human Factor;

Filing Info

• Accession Number: 00603696
• Record Type: Publication
• ISBN: 0-309-05060-X
• Files: TRIS, TRB, ATRI
• Created Date: Feb 28 1991 12:00AM