Reconfiguring Urban Undivided Four-Lane Highways to Five-Lane: A Nonideal but Very Effective Solution for Crash Reduction
Publication: Journal of Transportation Engineering, Part A: Systems
Volume 146, Issue 10
Abstract
Although a reconfiguration to three-lane with a left turn lane remains the most prevalent cost-effective countermeasure, some four-lane undivided highway segments in Louisiana have been reconfigured to five-lane segments with a left-turn lane by utilizing the existing pavement width basically at the cost of restriping. The current study analyzes nine locations where undivided four-lane roadways were converted to five-lane roadways in Louisiana urban areas with up to 7 years of before-and-after crash data. To avoid any potential regression-to-the-mean bias, the empirical Bayes (EB) method was used with the safety performance function (SPF) developed by the Louisiana Department of Transportation and Development (LaDOTD). Despite the contemplation in design guidelines and previous studies that a five-lane roadway is more crash-susceptible than a four-lane roadway, the safety effectiveness of conversion to five-lane was deduced to be significantly positive. Consistent crash reduction was observed in all sites, which resulted in a crash modification factor (CMF) of 0.48 with a small variance of 0.001. Expectedly, a substantial reduction in the target crash type, rear-end crashes, was achieved. This four-lane to five-lane conversion was found very effective specifically for urban and suburban roadways with annual average daily traffic (AADT) ranging from 15,000 to 30,000 and driveway density from 18 to 31 driveways per kilometer (30–50 driveways per mile). The high safety benefit-cost ratio, , indicates strong support to use this countermeasure on four-lane undivided roadways with additional evaluation for feasibility.
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Data Availability Statement
All data, models, or code generated or used during the study will be available from the corresponding author by request.
Acknowledgments
This study was sponsored by the Louisiana Transportation Research Center (LTRC). It was a part of the project “Investigating Safety Impact of Centerline Rumble Strips, Lane Conversion, Roundabout and J-Turn Features on Louisiana Highways.” The authors would like to acknowledge the support from all local district offices of the Louisiana DOTD. This study was presented in the 96th TRB annual meeting, and the comments by the discussants are greatly appreciated. The authors also would like to thank Jacob Moreau for his assistance in data processing.
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© 2020 American Society of Civil Engineers.
History
Received: Feb 28, 2019
Accepted: May 4, 2020
Published online: Jul 28, 2020
Published in print: Oct 1, 2020
Discussion open until: Dec 28, 2020
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