The Effects of Curb Extensions and Stormwater Infrastructure on Traffic Safety in Philadelphia

In order to meet the goals set out in the City's landmark stormwater management plan, and to satisfy state and federal regulations, the Philadelphia Water Department (PWD) is planning, designing, and constructing a portfolio of stormwater infrastructure systems. These systems capture, filter, and store stormwater run-off utilizing sub-surface trenches, and vegetated features, from raingardens to street trees, mimicking natural processes where possible. As part of this program PWD has developed 156 stormwater management bumpouts, and anticipates bringing 342 more online within the next 5 years. These bumpouts have vegetated curb extensions that protrude into the street at mid-block or intersection locations. When located at crosswalks, curb extensions are thought to improve traffic safety by reducing the crossing time of pedestrians, improving visibility at intersections, and slowing drivers by reducing the turning radii at intersections. This proposed project will examine the effects of these curb extensions over time on traffic collisions, injuries and fatalities relative to similar roadways where curb extensions will but have not yet been installed. Although pre-existing crash data featured in the selection of treated locations, the focus on stormwater management and long list of treated and untreated intersections provide unique, quasi-experimental conditions under which to examine the effects of curb extensions. Although curb extensions are widely accepted roadway design interventions in the fields of traffic calming and traffic safety, little is known about their effects on crashes or how these effects may vary by roadway conditions, location, or other features. While data processing is in progress, the City and Water Department have geocoded the locations of the existing and proposed curb extensions. Crashes from Pennsylvania Department of Transportation's (PennDOT’s) crash reporting system will be to the nearest intersection nodes of the eligible bump-outs. From here, the number of crashes, fatal and serious injury crashes, and injury crashes within each buffer can be counted and aggregated by year, with results associated with their corresponding intersection nodes and curb extensions.

• Record URL:
  • https://ppms.cit.cmu.edu/projects/detail/579

Language

• English

Project

• Status: Completed
• Funding: $180,000.00
• Contract Numbers:

  69A3552344811

  69A3552348316

• Sponsor Organizations:

  Office of the Assistant Secretary for Research and Technology

  University Transportation Centers Program
  Department of Transportation
  Washington, DC  United States  20590
• Managing Organizations:

  Safety21 University Transportation Center

  Carnegie Mellon University
  Pittsburgh, PA  United States  15213

  Carnegie Mellon University

  Pittsburgh, PA  United States 
• Performing Organizations:

  University of Pennsylvania

  ,    
• Principal Investigators:

  Guerra, Erick

  Hu, Yihong

• Start Date: 20250701
• Expected Completion Date: 20260831
• Actual Completion Date: 20260831
• USDOT Program: University Transportation Centers

Subject/Index Terms

• TRT Terms: Crash rates; Curbs; Drainage structures; Runoff; Traffic safety; Vegetation
• Geographic Terms: Philadelphia (Pennsylvania)
• Subject Areas: Design; Highways; Hydraulics and Hydrology; Safety and Human Factors;

Filing Info

• Accession Number: 02002847
• Record Type: Research project
• Source Agency: Safety21 University Transportation Center
• Contract Numbers: 69A3552344811, 69A3552348316
• Files: UTC, RIP
• Created Date: Sep 17 2026 2:57PM