Before & After Studies

• Starting in 2024, a section in the Vision Zero Mid-Year Reports will summarize findings and examples from before/after monitoring of quick-build projects, action spot improvements, and HIN safety audit action. The bullets below provide an excerpt of the before/after analysis by year: 
  • 2025 Mid-Year Before/After Crash Monitoring Summary Coming in September 
  • 2024 Mid-Year Before/After Crash Monitoring Summary(PDF, 130KB)
• Prior to 2024, we published before/after crash summaries on a one-by-one basis, which we realized was unsustainable. See below for the archived studies conducted in 2023 and earlier. 
  • 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

From 2023-2025, the County worked with third-party contractors to conduct a Tool-Based Before/After Studies project. The objective of the project was to evaluate how five engineering tools affected safety when applied in different location types in the County. 

The tools assessed and topline findings in the study include:

• Curb modifications: Resulted in minor decreases in right turn vehicle speeds; More effective when markings accompanied by flex posts; More effective when bike lane not present.
• Hardened centerlines: Resulted in significant decreases in left turn speeds and percentage of vehicles crossing the yellow line while turning; More effective when both mini speed humps and flex posts are installed for hardening.
• Tactical speed humps: Resulted in significant decreases in speeds and speeding in school zone corridors; More effective when placed away from STOP sign locations.
• Speed limit pavement markings in school slow zones: Resulted in minor decreases in average 85^th percentile speeds but helpful in reducing vehicles traveling above 30mph.
• No-turn-on-red signage: Resulted in moderate reduction in vehicles turning right on red; Some locations showed an increase in the amount of pedestrian/vehicle conflicts on the vehicular green/concurrent walk signal phases.

View the Before & After Studies Summary Report & Appendix here.(PDF, 8MB)

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. 

• Tactical Speed Humps on Three Additional School Slow Zone Corridors (Archive 2025)
• Temporary Bus Loading Platform at S Glebe Rd & S Old Glebe Rd (Archive 2025) 
• Tactical Speed Humps on Three School Slow Zone Corridors (Archive 2024) 
• Hardened Centerlines Safety Treatments at Five Intersections (Archive 2024) 
• School Crossing Improvements at Patrick Henry Dr & 18th St N (Archive 2022)
• Intersection Phasing & Lane Configuration Improvements at Fort Myer Drive & Eastbound Langston Blvd (Archive 2022)
• Temporary Roundabout Conditions at Military Rd & Nelly Custis Dr (Archive 2022)
• Temporary Lane Closure on S Carlin Springs Rd (Archive 2021)   

   

   

   

Since the adoption of Vision Zero, Arlington has implemented several initiatives to reduce speeds and improve safety on arterial roads throughout the County. After gathering data from before and after implementations, we’ve reviewed how effective these initiatives have been at reducing driver speeds. Learn more about each initiative below.

• In 2020 and 2021, we installed “$200 Additional Fine(PDF, 605KB)” signs on 12 roads.
• In 2021 and 2022, we reduced the speed limit on 14 roads(PDF, 688KB).
• From 2018 to 2022, we reconfigured the lanes on 14 roads(PDF, 6MB).