Federal yellow-light standards ignored on many Florida roads

3:18 PM, May 17, 2013   |    comments
  • Share
  • Print
  • - A A A +

TAMPA BAY, Fla. - According to the U.S. Department of Transportation (USDOT), municipalities should use a complex engineering formula to calculate yellow light intervals and maximize safety.  But 10 News learned the formula isn't being followed across much of Florida, resulting in short yellow lights, which create more red-light camera (RLC) citations.


The yellow interval formula takes into account the 85th percentile of drivers' speed on any given roadway, in order to allow most drivers enough time to stop at a signal safely.  But in 2011, the Florida Department of Transportation (FDOT) started using posted speed to calculate the interval instead, which is typically lower than average approach speed.

In many cases since 2011, FDOT worked with local engineers to reduce yellow-light times, but the agency's top traffic signal engineer, Mark Wilson, now confirms to 10 News that the reductions were a mistake and just about any request from local cities and counties to extend yellow intervals, based on federal safety guidelines, would be approved.

As a resource to local cities and counties, 10 News is providing those safety guidelines and RLC "best-practices":



  • USDOT and FDOT use the Institution of Transportation Engineers' (ITE) formula to calculate yellow intervals.  The most significant variable in the equation is the approach speed of a vehicle.
  • USDOT also recommends an extra ½ second of yellow time at intersections with lots of trucks or elderly drivers to allow them to react safely. (slide 28 on this report)
  • And the USDOT Red-Light Camera Systems Operational Guidelines indicates engineering studies should be conducted before RLC are installed.  Across Greater Tampa Bay, few - if any - municipalities conducted engineering reports before installing RLC.


  • Until 2011, FDOT required municipalities to calculate yellow light minimums based on the 85th percentile speed of vehicle travel.  But after the Mark Wandell Act (RLC bill) was passed in 2010, FDOT quietly changed the rules to allow communities to use posted speed limit in calculating yellow intervals, thus allowing them to reduce yellow light times: 4.0 seconds for a 40mph approach, 4.3 seconds for a 45mph approach, etc.
  • FDOT's top signal engineer, Mark Wilson, told 10 News that the state's new, shorter minimums for yellow intervals were never designed to be blanket rules for communities, but some FDOT district engineers were under the wrong impressions.


  • A USDOT report (slide 28 on this report) indicates when yellow light times are lengthened, severe crashes plummet.
  • Research indicates half of all red-light runners at short yellows occur in the first half-second, indicating drivers aren't "blatant" red-light runners, but simply caught in the "dilemma zone."
  • The dangerous "dilemma zone" grows larger as yellow times grow shorter.  


  • Per FDOT's Mark Wilson, "if a local agency provides information from a Fl PE that was based on their observations or studies, or their review and understanding of any nationally accepted research studies...then FDOT would approve this request."
  • Wilson added "I would say that FDOT would have no problem with approving an increase of up to 0.5 seconds," while increases of more than 0.5 seconds would require more documentation, like engineering reports.


This information was provided to numerous elected officials around Greater Tampa Bay by 10 News as a resource for analyzing their yellow light lengths.

Recipients include Tampa Mayor Bob Buckhorn, Tampa's city council, St. Petersburg Mayor Bill Foster, St. Petersburg's city council, New Port Richey's mayor and city council, Port Richey's mayor and city council, Pasco County's commissioners, Hillsborough County Commissioners, Manatee County commissioners, and numerous Tampa Bay legislators.

Find 10 News Investigator Noah Pransky on Facebook or follow his updates on Twitter. Send your story tips to noah@wtsp.com.

Most Watched Videos