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Safety Before & After Studies

The Vision Zero Action Plan states that we will review the efficacy of transportation safety mitigation measures by assessing conditions before and after implementation, which will inform future policies and implementation of such mitigation measures. This page summarizes the findings and next steps for before / after studies conducted on safety improvements, such as:

Location-Based Before/After Studies - Assessment of crash rates before/after quick-build improvements or other hot spot improvements were installed at a location.
Tool-Based Before/After Studies - Evaluation of the impact that an engineering tool has on safety across multiple locations.
Pilot Safety Project Before/After Studies - Evaluation of the impact that a pilot safety project had on addressing the identified safety issue.
Speed Management Before/After Studies - Assessment of before/after speeds along corridors with recent speed management treatments.

View the sections below to learn more about past or ongoing before/after analysis for each of these categories.

Location-Based Before/After Studies

N Glebe Rd and N Carlin Springs Rd(PDF, 182KB): Implemented Leading Pedestrian Interval (LPI)
- Avg Crashes/Year: 1.6 in 2016-2020 to 1.5 in 2021-2023
Little Falls Rd and Old Dominion Dr(PDF, 195KB): Tactical improvements to reduce turning conflicts
- Avg Crashes/Year: 11.4 in 2016-2021 to zero in 2021-2023
Clarendon Circle(PDF, 180KB) : Intersection reconfiguration included in transportation capital project (view project page)
- Avg Crashes/Year: 4.5 in 2014-2020 to 4 in 2020 2022
West Bound Langston Blvd & N Lynn St(PDF, 172KB): Intersection and sidewalk improvements as apart of a joint project between the County and VDOT (view project page)
- Avg Crashes/Year: 7.5 in 2014-2020 to 4 in 2020-2022
Fairfax Dr & 14th and Queen St(PDF, 224KB): Quick-build response to crash hot spot (view project cut sheet)
- Avg Crashes/Year: 3.4 in 2014-2020 to 0.5 in 2021-2022
Fort Myer Dr & Fairfax Dr(PDF, 189KB): Lane reconfiguration included in repaving effort (view before/after images(PDF, 137KB))
- Avg Crashes/Year: 3.25 in 2014-2017 to 2.2 in 2018-2022
Eastbound Langston Blvd & Fort Myer Dr(PDF, 214KB): Signal phasing and lane removal as part of pilot project (view project sheet)
- Avg Crashes/Year: 8.1 in 2014-2021 to 3 in 2021-2022
N Meade St & Arlington Blvd(PDF, 152KB): Tactical improvements responding to crash hot spot (view project cut sheet)
- Avg Crashes/Year: 4.3 in 2014-2020 to 3 in 2020-2022
N Quincy St & 10th St N(PDF, 193KB): Median and signage improvements responding to crash hot spot
- Avg Crashes/Year: 2 in 2014-2019 to 0.67 in 2020-2022
Pershing Dr and N Irving St(PDF, 269KB): Stop sign added to address crash pattern
- Avg Crashes/Year: 3.25 in 2014-2017 to 0.5 in 2018-2022
Richmond Highway & N Marshall Dr(PDF, 183KB): Advanced signage responding to crash hot spot
- Avg Crashes/Year: 8.3 in 2014-2020 to 3 in 2021-2022
Yorktown Blvd & N George Mason Dr(PDF, 213KB): Tactical improvements responding to systemic safety risk (view before/after images(PDF, 152KB))
- Avg Crashes/Year: 0.75 in 2014-2017 to 0.6 in 2018-2022

Tool-Based Before/After Studies

Coming soon!

Pilot Safety Project Before/After Studies

Whenever we install a pilot safety project, we identify performance metrics so we can study whether the project is successfully addressing safety concerns through either quantitative or qualitative measures. See below for examples of before/after performance tracking for completed Vision Zero safety pilot projects. For more information about each project, please visit the Safety Pilot Projects page.

Speed Management Before/After Studies