United States Department of Transportation
i
Impact of new speed limits on Kansas highways
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2000-11-01
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[PDF-237.86 KB]
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Abstract:On November 28, 1995, the National Highway System (NHS) Designation Act abolished the federal mandate for the National Maximum Speed Limit (NMSL) and returned the authority of establishing speed limits to the states. By the end of 1996, 32 states had passed laws to raise speed limits on various highways. Accordingly, Kansas' law increased speed limits on most of its highways in March 1996. The detailed research study reported herein concentrated on analyzing the before and after Kansas' speed and accident databases. In regard to speed analysis, the t-test was applied to investigate whether significant increases in 85th percentile speeds were noted during the after period on both interstate and 2-lane rural highways. In this case, a 3-mph increase in 85th percentile speeds was noted on interstate highway sections and a 3 to 5 mph increase was noted on the 10-mph speed limit increased 2-lane highways. None was noted on the 5-mph speed limit increase on the 2-lane highways.
The 3-Step Sequential Analysis approach was utilized to analyze the before-and-after Kansas' accident database. By performing the analysis, it was concluded that, as of 1998, no statistically significant increases in crash, fatal crash and fatality rates were noted during the after period on either rural or urban interstate highway networks. On the other hand, statistically significant increases in crash, fatal crash and fatality rates were observed on the 2-lane rural highway network. Subsequent detailed analysis on the 2-lane highway databases filtered out all highway sections that have experienced, during the after period, the most significant increases in crashes (MSICR). Additionally, it is concluded that those MSICR sections (represent about 7% of the entire 2-lane rural highway network sections) have accounted for most of the noted significant increases in crash and fatal crash rates. Fatal crashes on the remaining 93% of the 2-lane rural network were found to be less than those observed during the before period.
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