Long Term Impact of Differential Speed Limits on Rural Freeways in Idaho
The main focus of this research is to evaluate the long-term operation and safety impact of Differential Speed Limits (DSL) on rural freeways in Idaho. The analysis of speed data covered three periods: period 1: January 1992 - April 1996 (Uniform Speed Limit (USL) of 65 mph); Period 2: April, 1996 - June, 1998 (with a USL of 75 mph); and Period 3: July, 1998 – December, 2011 (with a DSL of 75 mph for passenger cars and 65 mph for commercial truck vehicles). The analysis showed that since the implementation of the DSL policy, Idaho’s speed trends have stabilized with no sizable change. The mean speed for trucks and passenger vehicles are very close to their respective posted speed limits. The 85th percentile speeds have also stabilized at about five mph above the respective speed limits. DSL implementation also visibly improved the compliance rate of truck speed limit. The considerable reduction in the 85th percentile and the pace speeds for trucks and the improved speed limit compliance rate indicate that the DSL policy favorably impact truck driver behavior by reducing the most extreme truck speeds. Implementation of the DSL policy has contributed to the improved safety conditions on rural freeways in Idaho. Crash rate analysis showed that DSL favorably affects safety. Crash rates for all crash types were highest during the period 1996 to 1998 with a USL of 75 mph. When DSL policy was implemented in 1998, the crash rates decreased considerably and continued to decline since then.
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Supplemental Notes:
- This paper was sponsored by TRB committee ANB20 Safety Data, Analysis and Evaluation.
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Corporate Authors:
500 Fifth Street, NW
Washington, DC United States 20001 -
Authors:
- Elbassuoni, Sherief
- Dixon, Michael
- Abdel-Rahim, Ahmed
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Conference:
- Transportation Research Board 94th Annual Meeting
- Location: Washington DC, United States
- Date: 2015-1-11 to 2015-1-15
- Date: 2015
Language
- English
Media Info
- Media Type: Digital/other
- Features: Figures; Maps; References; Tables;
- Pagination: 15p
- Monograph Title: TRB 94th Annual Meeting Compendium of Papers
Subject/Index Terms
- TRT Terms: Crash rates; Highway safety; Passenger vehicles; Rural highways; Speed limits; Trucks
- Geographic Terms: Idaho
- 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: 01554246
- Record Type: Publication
- Report/Paper Numbers: 15-5844
- Files: TRIS, TRB, ATRI
- Created Date: Feb 26 2015 9:49AM