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Type of Document Thesis Author Muchuruza, Victor Author's Email Address vmuchuruza@eng.fsu.edu URN etd-12032003-150846 Title Evaluating the Relevance of 40 MPH Posted Minimum Speed Limit on Interstate Freeways Degree Master of Science Department Civil and Environmental Engineering, Department of Advisory Committee
Advisor Name Title Renatus Mussa Committee Chair John Sobanjo Committee Member W. Virgil Ping Committee Member Keywords
- Minimum Speed Limit
- 15th Percentile Speed
- Speed Variability
Date of Defense 2003-11-17 Availability unrestricted Abstract The practice of posting minimum speed limits on rural Interstate freeways is predicatedon the desire to reduce vehicle conflicts caused by speed variability in a traffic stream. In some
states, minimum speed limit signs are posted on rural interstate freeways and other limited access
facilities. However, the relevance of the 40 MPH minimum speed limit posted on Florida
Interstate freeways system is increasingly being questioned in light of the increase of maximum
speed limit to 70 MPH following the National Highway System (NHS) Designation Act of 1995
which repealed the federally sanctioned maximum speed limit.
This study was aimed at evaluating the operational and safety characteristics of Florida
Interstate freeways with 40 MPH minimum speed sign. Speed and crash data were collected on
four major Interstate freeways in Florida. The speed data revealed that the 15th percentile speed
on all sites is 60 mph or above on both four-lane and six-lane freeways sections. The average
speeds on all sites were approximately five standard deviations above the 40 mph speed value.
The coefficients of variation ranged from 7 to 11 percent while the trimmed variance analysis
showed that vehicles traveling below 55 mph had insignificant contribution to the variation of
traffic speeds. Comparison of speed data collected prior to raising the speed limit from 65 mph
to 70 mph showed that the average speeds increased by 5 mph while the variances did not
change significantly. However, the coefficients of variation have increased significantly.
The analysis of safety experience on these freeway sections revealed that speed variation
is potentially a contributing factor to the majority of the crashes analyzed. Stratification of crash
involved vehicles by speed showed that vehicles traveling with speeds below 40 MPH were
overrepresented. The research further discusses safety modeling using Poisson regression.
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