Abstract
Suitable speed limit is important for providing safety for road users. Lower-than-required posted speed limits could cause the majority of drivers non-compliant and higher-than-required posted speed limits may also increase the number of crashes with related severities. The speed limit raised in Kansas from 70 mph to 75 mph on a number of freeway segments in 2011. The goal of this study is to assess the safety impacts of the freeway sections influenced by speed limit increase. Three years before and three years after speed limit increase was considered and three methods were used: 1-Empirical Bayes (EB), 2-before-and-after with comparison group, and 3-cross-sectional study. The Crash Modification Factors (CMFs) were estimated and showed 16 percent increase for total crashes according to EB method. Further, the before-and-after with comparison group method showed 27 percent increase in total crashes and 35 percent increase on fatal and injury crashes. The cross- sectional method also presented 25 percent increase on total crashes and 62 percent increase on fatal and injury crashes. It was seen that these increases were statistically significant.
Highlights
The relationship between speed limit and the number of crashes is an important subject to vehicle insurance companies and general public
Average Daily Traffic (AADT), roadway width, shoulder width, shoulder type, surface type, number of lanes, functional classification, and posted speed limit were selected as explanatory variables and the results showed that the degree of curve and posted speed limit were statistically significant on number of crashes [13]
The results present how total crashes and fatal and injury crashes have changed after speed limit increase according to each method
Summary
The relationship between speed limit and the number of crashes is an important subject to vehicle insurance companies and general public. Correct speed limits are essential for increasing the safety on highways and streets for any driver who is not familiar with the roadway at all. In 2011, speed limit increased from 70 mph to 75 mph on more than 800 miles of freeways in Kansas. The goal of this study is to assess the safety consequences of the roadways affected by the speed limit increase. Previous research studies that considered the traffic safety effect due to speed limit changes showed significant results as follows
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