United States Department of Transportation
i
Speed limit recommendation in vicinity of signalized, high-speed intersection.
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2012-04-01
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[PDF-3.90 MB]
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Edition:Final report.
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Abstract:We evaluated the traffic operations and safety effects of 5 mph and 10 mph speed limit reductions in the vicinity of highspeed,
signalized intersections with advance warning flashers (AWF). Traffic operational effects of the reduced speed
limits were analyzed for seven high-speed, signalized intersections with AWF using the Quantile regression model and
Seemingly Unrelated Regression Estimation (SURE). Change of speed limit from 60 mph to 55 mph did not lead to any
statistically significant reduction in 15th, 50th, or 85th percentile. The reduction from 65 mph to 55 mph hour led to a 4.6
mph reduction in 85th percentile speed; also, the speed dispersion based on inter-percentile range between 15th and 85th
percentiles was reduced by 1.8 mph. About the mean and standard deviation of speed estimated by SURE, the only
statistically significant impact is from the speed limit reduction of 10 mph from 65 mph, which reduced the mean speed of
vehicles by 3.8 mph at the significance level of 95%. In the safety effect study, a crash analysis based on 56 approaches
from 28 intersections was performed. The 10 mph speed limit reduction from 65 to 55 mph was found to reduce, on an
average, 0.4 crashes per approach per year with 90% percent level of confidence while the 5 mph reductions in the dataset
was found to reduce, on an average, 0.6 crashes per approach per year with 95% significance level. Also, the studied
approaches with 10 mph reduction were found to have a lower probability of possible injury crashes and a higher
probability of property damage crashes with a 90% level of confidence. The 5 mph reductions in this dataset did not show
any significant effect on reducing crash severity. It was also found that lower speed limits in vicinity of the signalized
intersection reduced the probability of fatal and injury crashes.
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