Drivers may soon get a small reprieve when there's no time to brake for some stoplights.
By the end of this year, Missouri Department of Transportation engineers will slightly lengthen the yellow light timing at many of the roughly 2,000 traffic signals on state-controlled roads and highways. MoDOT officials hope that adding a few fractions of a second may reduce the number of traffic accidents at those intersections.
The move is driven by a national study that encouraged traffic engineers to give more weight to vehicle stopping distances at traffic signals, said Tom Blair, MoDOT's assistant district engineer in St. Louis. Those distances are heavily influenced by the car's speed and by driver distraction.
"Our staff looked at this one and said it is about time we look at the motorist's ability to stop," Blair said.
MoDOT's review also looks at the width of the intersection.
Don Hillis, MoDOT's assistant chief engineer in Jefferson City, said the state previously based signal timing on the need to move as many cars as possible through an intersection. Many signal intervals were fairly uniform. But a recent study suggested that intersections don't lend themselves to a one-size-fits-all approach.
Cars approach intersections at different speeds, and intersections have different dimensions, he said.
Since the work began earlier this year, Blair said, the time added to yellow lights in the St. Louis area has ranged from tenths of a second to 1.6 seconds in the case of Highway 141 and Astra Way in Arnold. The city was the first in Missouri to introduce red light cameras — including the one at that intersection.
Since the state increased the timing of the yellow light on Highway 141, the number of red light camera tickets has declined.
In addition to the intersection of Highway 141 and Astra, Arnold has installed red light photo enforcement cameras at three other locations. Based on figures compiled by the Arnold Police Department, the number of red light camera tickets recorded throughout the city dropped from 691 in January to 95 in May.
During that time, the most noticeable drop was at Highway 141 and Astra.
"There is no question that engineering, enforcement and education all play a role in reducing red light running," said Charles Territo of American Traffic Solutions, the city's vendor.
When engineers set yellow light signal timing, Territo said, they do so to optimize safety and traffic flow. But he said artificially lengthening the yellow light time could backfire by encouraging drivers to drive faster through the intersection.
A drop in traffic citations "is a good news story," said Territo, the company's vice president of communications, because "the goal of all programs is to change driver behavior."
But Matt Hay, a former Arnold councilman and founder of the website WrongOnRed.com, said the number of citations had actually risen over time — until the yellow light was lengthened. That cuts against heightened public awareness, he said.
Arnold Councilwoman Doris Borgelt agreed. Borgelt, a longtime critic of the red light cameras, has even pushed for flashing yellow lights on Highway 141 alerting motorists to stop when approaching the Astra intersection.
"What it suggests to me is that all along the timing needed to be changed," Borgelt said. "I have always advocated for a longer yellow light. A true safety measure."