A pilot project testing the effects of increasing the yellow warning time at intersections continues to demonstrate positive results in Denton, Texas. In April 2018, the city decided to appease red light camera critics by adding a second of yellow time to the photo enforced intersection of West Oak Street and North Carroll Boulevard. To the surprise of city staff, the 62 percent reduction in violations that began the day the timing was extended has lasted for ten months. Staff is now recommending a modest expansion of the test at the most profitable red light camera location.

"Using the number of violations as a guide, staff is recommending to extend the pilot program (adding one second to the yellow signal interval) to the signals for both the northbound and southbound cameras at the intersection of I-35E and US 377 beginning March 1, 2019," a city staff report recommended on Friday.

Defenders of photo enforcement have claimed the benefits of extending yellow warning times dissipates over time. Denton's data show that the boost in yellow time from 3.5 seconds to 4.5 seconds has the same effect now as it did on the first day. There was a 64 percent drop in yellow in December 2018 compared to the previous year under the shortened yellow (view the city's chart). By contrast, there has been no reduction in the number of alleged violations at the twelve other red light camera locations in the city. The safety impact has also been positive.

"Since January 2016, there have been a total of 17 accidents at the intersection," staff noted. "Since the pilot program began at this intersection in April 2018, there have been four accidents reported."

Councilman Keely G. Briggs called for the pilot project. City staff revealed the data about the improvement at the intersection at her request. In other jurisdictions, municipal officials have resisted extending yellow light times. For that reason, the states of Georgia and Ohio mandated an extra second of yellow at every location equipped with a red light camera. Once the law was implemented, Georgia's red light violations immediately plunged between 70 and 80 percent, and in Ohio violations likewise plummeted as drivers had more time to get through intersections safely. The benefits did not decline over time, as TheNewspaper documented with a review of four years of data. Similar findings have been made in Chandler, Arizona and San Carlos, California.

A study by the Texas Transportation Institute explained that the majority of straight-through red light violations happen when a driver misjudges the end of the yellow light by less than 0.25 seconds (view chart). The TTI study confirmed that longer yellows also reduced accidents (view report).

A copy of the staff report is available in a 600k PDF file at the source link below.