National Investigation of the Environmental, Safety and Livability Impacts of Travel Lane WidthEvidence from 10 American Cities

Evidence from 10 American Cities

Principal Investigator(s): Shima Hamidi PhD, Ebrahim Azimi PhD, Reid Ewing PhD

Project Partners: Johns Hopkins Bloomberg School of Public Health, University of Utah, Bloomberg American Health Initiative, Johns Hopkins Center for Injury Research and Policy, Bloomberg Philanthropy

Research Project Funding: $244,163

Project Start and End Date: Oct 1st, 2023 – September 30st, 2024

Project Description: This project is one of the most comprehensive efforts to date to address a long overdue built environmental and transportation challenge to health: unnecessarily wide travel lanes that are designed to accommodate fast and convenient driving. There has been a constant competition for space in roadways’ right-of-way. In most American cities, the automobile is the winner of this competition, making it a challenge to find space for bike lanes and sidewalks. One of the easiest and most cost-efficient way to make space for cyclists and pedestrian is to narrow travel lanes and parking lanes to an optimal width. The main drawback is safety concerns. Are wider lanes safer? A recent study in seven US Cities by the PI found that narrower lanes do not have a higher number of crashes than their wider counterparts, after controlling for 21 functional and design street characteristics. This study builds on the earlier effort by 1) expanding sample to more than 1,500 street sections with three additional cities and measuring a comprehensive set of 21 microscale street design features for these streets; 2) quantifying the impact of narrow travel lane on traffic fatalities, pedestrian safety, and bicycle safety indicators; and 3) measuring the impact of narrow lane width on pedestrian volume and activities. Finally, from the national sample of ten cities, the PIs will select one lane width reduction project for further longitudinal analysis of traffic speed, roadway capacity (traffic volume), roadway safety (crash severity and frequency) and GHG emission impacts before and after the lane width reduction. The findings will lead to a set of policy and practical recommendations for local and state DOTs. The study will identify best candidates for lane width reduction projects in these ten cities and offers insights on how to prioritize lane width reduction without compromising safety. Furthermore, the findings will provide insights on what best practices strategies on how to plan best for the additional space as a result of lane width reduction to achieve thoroughly multimodal transportation network.

US DOT Priorities: This project fits well within the US DOT Strategic Goals of Climate and Sustainability and Safety, aiming to provide a data-driven approach to street design and specifically identifying optimal lane width in different contexts that will lead to a more sustainable multimodal street network without compromising safety. The project also fits perfectly with CCST’s Focus Area 4 “VMT & GHG Reduction via Modal Shift and Changes in Travel Behavior” and Focus Area 1 “Promoting Climate Culture in All Levels of Transportation Decisions”.

Outputs: This study will produce the following outputs:

  1. Profiles of lane width for more than 1,500 street sections in 10 major U.S cities
  2. Final profiles of best candidates for lane-width reduction projects in 10 US cities
  3. A peer-review journal article on the safety impacts of narrow travel lanes
  4. A peer-review journal article on the introduction of robust methodology for measuring microscale roadway design characteristics using AI and machine learning technologies.
  5.  A peer-review journal article on the environmental/pedestrian activity impacts of narrow travel lanes
  6. 3 Conferences and one UTC lecture presentations
  7. Final report to CCST, state and local DOT agencies  
  8. A policy paper summarizing the relevant findings for practitioners.

Outcomes/Impacts: Car dependency, coupled with the lack of walking and biking infrastructure, has led American cities to have substantially lower rates of pedestrian and cyclists and significantly higher rates of pedestrian and bicyclist crashes/fatalities, compared to their European counterparts. Narrowing lane width not only could address safety issues for cyclists and pedestrian, but it also addresses critical environmental challenges by accommodating more users in less space, using less asphalt pavement and less land consumed and also contributes to enhancing community livability, public health, and economic development.

The dataset and findings of this study will help state DOTs to identify areas for roadway reconfigurations, and implement roadway design improvements for multi-modal mobility, such as pedestrian refuge islands, transit shelters, bicycle lanes, on-street parking, or traffic calming measures. In addition, the findings of this study could be directly incorporated into the state DOT’s Highway Safety Improvement programs in our sample (especially non-infrastructure projects such as crash prediction models), as well as the local level safety and sustainability programs to improve roads and intersections on local streets. The study results will help to prioritize segments that need lane width adjustment which can then be integrated with the state DOT’s Reconstruction, High Volume Road (HIV), and Low Volume Road (LIV) programs.