Safety Performance of Edge-Lane Roads
Publication: Journal of Transportation Engineering, Part A: Systems
Volume 148, Issue 11
Abstract
This paper provides an observational before/after evaluation of the safety effects of edge-lane road (ELR) (also known as advisory bike lanes or advisory shoulders) installations in the United States. An ELR is a class of roadway that supports two-way automobile traffic within a single center lane and vulnerable road users (VRUs), i.e., bicyclists or pedestrians, in the edge lanes on either side. The use of a single lane by automobile users traveling in both directions is often a cause of potential safety concerns among the general public. This study employs a project-level empirical Bayes (EB) approach to before/after safety analysis for all US ELR sites where requisite crash data and other relevant characteristics were available. The analysis at 11 sites was performed with 8 years of crash data and more than approximately 60 million motor vehicle trips. Project-level EB analysis based on safety performance functions (SPFs) showed 8 of 11 ELR sites experienced a reduction in crash experience since installation. There was a reduction in crashes among all sites compared to the expected crashes on the traditional two-lane two-way design that existed before ELR installation. This estimation assumed the calibration factor for all SPFs used in the EB analysis was 1.0. Because of the geographical spread of the ELRs being analyzed in this study, estimation of specific calibration factors for all 11 sites was beyond the scope of this work. To address this limitation, we conservatively assumed the SPF calibration factors to be 0.50 for locations for which calibration factors were not available. This assumption was made for 7 of the 11 sites. Even with this conservative assumption, the ELRs were estimated to have a crash reduction. The results from this comprehensive evaluation of existing US ELRs should alleviate concerns the general public often has about the safety of ELRs for automobile users.
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Data Availability Statement
Some or all data, models, or code that support the findings of this study are available from the corresponding author upon reasonable request.
Acknowledgments
This study was conducted as part of a study funded by California SB1 funds provided via the Mineta Transportation Institute (MTI). Funding and final editing of a report published by MTI were the only roles performed by MTI on this project. The data collection effort was assisted by the following students: Abigail Matheny, Blake Thomas, Emily Lin, Eza Gaigalas, Ashley Yao, and Jacob Hamada. Help with obtaining crash data on US facilities was kindly provided by Derek Leuer and Ian Saari of the State of Minnesota; Stephen Buckley of Scarborough, Maine; Scott Robinson and Michael Stewart of Bloomington, Indiana; Kelly Campbell of the State of Idaho; and Andrew Hogle of the State of Colorado. Calibration factors for SPFs rural two-lane roads in Maine were provided by Mr. Dennis E. Emidy, who is a safety engineer in the Office of Safety and Mobility at Maine DOT. Dr. Karen Dixon of the Texas A&M Transportation Institute created, and commented on the use of, the spreadsheets that implemented the HSM worksheets used in the EB analysis. Mr. Nick Sauciur provided support for the final formatting of the paper.
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Information & Authors
Information
Published In
Journal of Transportation Engineering, Part A: Systems
Volume 148 • Issue 11 • November 2022
Copyright
© 2022 American Society of Civil Engineers.
History
Received: Sep 19, 2021
Accepted: Jun 2, 2022
Published online: Aug 31, 2022
Published in print: Nov 1, 2022
Discussion open until: Jan 31, 2023
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