Safety and operational impacts of setting speed limits below engineering recommendations

This study quantifies the operational and safety impacts of setting posted speed limits below engineering recommendations using field data from rural roads in Montana. Vehicle operating speeds and historical crash data were collected at multiple sites with posted speed limits set equal to engineering recommendations and sites with posted speed limits set lower than engineering recommendations. Linear, quantile and logistic regression models were estimated to predict mean operating speed, 85th percentile operating speed and speed limit compliance, respectively, as a function of various roadway characteristics and level of speed enforcement. The Empirical-Bayes before-after approach was also used to develop crash modification factors (CMFs) that describe the expected change in total and fatal + injury crash frequency when setting posted speed limits lower than engineering recommendations. Because safety data were collected over a long time period, temporal adjustments were incorporated to account for yearly changes in crash reporting, traffic characteristics and other variables. The results revealed that speed limit compliance worsened as the difference between the engineering recommended and posted speed limits increased. The presence of verified heavy police enforcement reduced both mean and 85th-percentile operating speeds by approximately 4 mph and increased speed limit compliance. The safety analysis found a statistically significant reduction in total, fatal + injury, and property damage only (PDO) crash frequency at locations with posted speed limits set 5 mph lower than engineering recommendations. Locations with posted speed limits set 10 mph lower than engineering recommendations experienced a decrease in total and PDO crash frequency, but an increase in fatal + injury crash frequency. The safety effects of setting speed limits 15 to 25 mph lower than engineering recommendations were less clear, as the results were not statistically significant, likely due to the small sample of sites included in the evaluation. Overall, the results suggest that setting posted speed limits 5 mph lower than the engineering recommended practice may result in operating speeds that are more consistent with the posted speed limits and overall safety benefits.

Record URL: https://doi.org/10.1016/j.aap.2018.08.029

Record URL: http://www.sciencedirect.com/science/article/pii/S0001457518305499

Availability: Find a library where document is available. Order URL: http://worldcat.org/issn/00014575

Supplemental Notes: © 2018 Elsevier Ltd. All rights reserved. Abstract reprinted with permission of Elsevier.

Authors: Gayah, Vikash V 0000-0002-0648-3360 Donnell, Eric T Yu, Zhengyao Li, Lingyu

Publication Date: 2018-12

Language

English

Media Info

Media Type: Web

Web Features: Figures; References; Tables;

Figures; References; Tables; Pagination: pp 43-52

pp 43-52 Serial: Accident Analysis & Prevention Volume: 121 Issue Number: 0 Publisher: Elsevier ISSN: 0001-4575 Serial URL: http://www.sciencedirect.com/science/journal/00014575



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