Engineers: Florida's yellow lights still too short at red light camera intersections

9:23 AM, Mar 4, 2014   |    comments
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TAMPA BAY, Florida - Nearly a year after 10 Investigates exposed short yellow lights at red light camera intersections and the state required cities and counties to extend the yellow intervals, some engineers say the lights still aren't long enough in Florida.

A number of critics of Florida's yellow light times recently took professional Lidar guns to Tampa Bay roads, prompted by the findings of 10 Investigates' red light camera series. Jim Walker, director of the National Motorists Association (NMA), and Joe Bahen, a Virginia traffic engineer who is also a member of the non-profit NMA, are trying to prove drivers didn't have enough time to stop at red light camera intersections.

The faster cars travel, the more time drivers need to slow down safely for a red light. Walker and Bahen claim Florida's yellow lights are often 0.5 seconds or more too short, because the state no longer factors drivers' actual speed into calculations, even though national guidelines recommend it. Instead, Florida yellow light times are calculated based on speed limits of the road.

But speed limits are typically set a few miles per hour below what engineers consider a roadway's "safe" speed. Prevailing engineering theories indicate 85% of motorists drive safely on any given road, so the 85% percentile speed is considered "safe."

TIMELINE: 10 News' Short Yellows Investigation
MAP: Short Yellows in Your Neighborhood

Florida used to follow national recommendations in factoring 85th percentile speed into yellow light times, but the provision was eliminated in 2010, resulting in much shorter yellow lights, including at red light camera intersections. 

"Most drivers are not driving the speed limit, but most drivers are driving safely," Walker said. "A lot of very safe drivers are going to get (red light camera) tickets they don't deserve."

The Inside Algebra

The faster a car drives, the more time it needs to stop. But the USDOT advises against using yellow lights or red light cameras as a speed deterent, suggesting it could cause "more red-light violations and higher crash rates."

Instead, yellow light calculations are recommended to factor the actual speed of 85% of drivers, so the majority of drivers have enough time to make safe decisions at yellow lights. In Florida, however, the yellow minimums are based on the speed limit of the roadway.

There are three other variables in the Florida Department of Transportation's (FDOT) yellow light formula, created by the Institute of Traffic Engineers (ITE):

  • Perception-reaction time (recently increased by FDOT from 1.0 second to 1.4 seconds)
  • Deceleration rate (10 ft/sec/sec)
  • Slope of the road (typically zero in Florida)

Mark Wilson, FDOT's top signal engineer, told 10 Investigates while the agency no longer uses the recommended 85% percentile speed variable, it now has "appropriate" yellow light lengths because of its conservative standards for PRT and deceleration rate. He added FDOT also now rounds up on all calculations, meaning every yellow light in the state should now be longer than the current federal minimum values, which are 3.0 seconds each.

"When you run the analysis, we're longer than most states," Wilson said of Florida's yellow lights. "We think the changes we made last year (will) improve the operation of the signal."

Wilson added in an e-mail that using all conservative variables "will produce a yellow interval that is much longer than needed, and could produce a condition that would increase rear-end crashes."  He also rejected a recent National Cooperative Highway Research Program suggestion that agencies could add 7 mph to any posted speed limit to approximate 85th percentile and allow drivers ample time to slow down at a yellow light.

But Walker and Bahen compiled a series of reports from Tampa and St. Petersburg intersections that indicate using the 85th percentile (or an approximation) would add at least half a second of yellow to every approach analyzed.

At several approaches, the 85th percentile speed was 10 miles per hour faster than the posted speed.

Wilson said FDOT would review the 85th percentile findings to see if speed limits need to be raised - and thus yellow light times as well - on any of the following roads:

Intersection City Posted Speed Limit 85th Percentile Difference in Yellow Light Time
Hillsborough Ave. EB at 22nd St. Tampa 40 mph 49 mph 0.7 seconds
Hillsborough Ave. WB at 22nd St. Tampa 40 mph 47 mph 0.5 seconds
Florida Ave. SB at Busch Blvd. Tampa 45 mph 47.5 mph 0.2 seconds
Busch Blvd. EB at Florida Ave. Tampa 40 mph 49.5 mph 0.7 seconds
Busch Blvd. WB at Florida Ave. Tampa 40 mph 50 mph 0.7 seconds
50th St. SB at Adamo Dr. Tampa 40 mph 50 mph 0.7 seconds
50th St. NB at Adamo Dr. Tampa 40 mph 48 mph 0.6 seconds
Gandy Blvd. EB at Westshore Tampa 45 mph 53 mph 0.6 seconds
4th St. SB at Gandy Blvd. St. Pete 40 mph 48 mph 0.6 seconds
4th St. NB at Gandy Blvd. St. Pete 40 mph 50 mph 0.7 seconds

With the majority of red light camera tickets coming in the first half-second of a red light, every extra fraction of a second could help drivers avoid potentially unfair tickets.

Recently, 10 Investigates showed how the recent 0.4- and 0.5-second extensions have virtually eliminated red light camera revenue at certain intersections.

The Push Against Longer Yellows

While FDOT recently extended yellow light minimums following 10 Investigates' stories, it decided not to return to using the 85th percentile speed (or an approximation) to calculate yellow light times.

Public records requests by 10 Investigates reveal a number of state and local engineers opposed using the 85th percentile, even though some acknowledged in e-mails that longer yellows may be safer for drivers.

"Please tell Mark Wilson not to use the 85th percentile," wrote City of Tampa signal engineer Mike Scanlon. "Too many variables. When do you measure? How far upstream do you take the measurement? What approach.? Will we have to do a speed study on each approach?? No way I can perform this many speed studies and still do timings!!!!!"

However, the City of Tampa conducts dozens of speed surveys a year. And the recent federal research indicates adding 7 mph to the posted speed would be a suitable alternative.

Yet, FDOT chose to leave drivers' actual speed out of its yellow light calculations, leaving drivers with a little less time to stop safely at intersections.

Will Yellows Get Longer?

Wilson said FDOT does not have any plans to adjust its yellow light minimums, but the legislature could change his mind for him.

A number of efforts to reform red light cameras in Florida are moving through the Capitol, and the topic of yellow-lengthening legislation has been a frequent conversation.

Governor Rick Scott, however, has not provided any indication of his support for red light cameras laws, even though 10 Investigates asked him several times in recent months.

Find 10 News Investigator Noah Pransky on Facebook or follow his updates on Twitter.


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