City data supports officials’ claims of flashing yellow lights’ safety

Data shows lights as safe as before, despite recent collisions

Flashing yellow arrows

Flashing yellow arrows have actually made the Bellevue’s signaled intersections safer over the last ten years, despite public perception otherwise, city data shows.

The flashing yellow arrows allowing motorists to turn left after yielding have become a more common sight in Bellevue in the last five years and a controversial issue in the community, with naysayers saying they allow drivers to make reckless moves and haven’t been cost effective.

“The safety of these lights presume that drivers obey rules of the road, including cell phone use, which we all know isn’t the case,” said Bellevue resident Tobiatha Tucker.

Doubts were raised after the death of a toddler in late September at a flashing yellow arrow on 140th Avenue Northeast. Shortly after the accident, city traffic representatives said the lights are safe and improve the flow of traffic, a fact substantiated by data recently obtained by the Reporter.

According to the data, while left turn collisions at intersections with traffic lights have increased overall, the average number of accidents at intersections in which drivers must yield before turning left – with both flashing yellow lights and solid green lights – actually dropped from earlier in the decade.

In 2004, there were 76 accidents at the 135 individual lights in the city where drivers had to yield before turning left. Ten years later, that number had increased to 112 collisions at 225 “protected-permissive” lights – an accident-to-light ratio of to just over .5 in 2014 compared to around .56 in 2004 (or for every 100 permissive left-turning lights, there were 56 collisions). There are currently 249 individual protected-permissive lights in Bellevue.

A protected-permissive left turn is one which has a protected phase (i.e. a solid green arrow) and a permissive one (a green ball or more commonly today a flashing yellow arrow) where the motorist must yield to oncoming traffic and pedestrians. They are also known as “pro-per” lights.

The city began installing the flashing yellow arrows as an alternative to the green ball lights in 2010. The Federal Highway Administration completed a comprehensive study in 2006 which found that flashing yellows were the best alternative to the green ball lights.

“[Flashing yellow arrows were] found to have a high level of understanding and correct response by left-turn drivers, and a lower fail-critical rate than the circular green,” the report’s summary states.

The ratio of pro-per lights to collisions decreased sharply once the lights began to be installed in 2010, and the ratio has fluctuated since.

The year with the highest ratio in the last 11 years was 2005, when the 137 permitted-lefts in Bellevue saw 87 collisions. The lowest two ratios (and lowest number of left-turning collisions overall) were actually the first two years the flashing yellow arrows were installed — 2010 and 2011. The ratio has risen slightly since.

Despite the Federal Highway Administration’s findings and the fact that these lights have existed in Bellevue since 2010, at many of the newly installed lights in the city, special signage marked with orange flags reminds motorists how to use the lights.

Critics claim that the lights allow drivers to be more reckless.

“I don’t buy the City’s explanation at all,” Douglas Rosenberg said after an earlier Reporter article in which city officials maintained the lights were safe. “I was also almost run over twice by these “flashing yellow” lights (because of a different reason) because cars making left hand turns are trying to avoid cross traffic cars and not focusing on pedestrians crossing who have a cross walk.”

Bellevue’s traffic engineering manager Mark Poch said the city goes through an extensive checklist before installing a flashing yellow arrow.

“The criteria to put in a permissive left turn includes speed and traffic volumes at different times of day,” he said. “And then we have a performance monitoring program. We check on collisions at the intersections twice a year.”

Even then, Poch said, sometimes the criteria fails.

“We try to identify locations where the lights aren’t working,” Poch said. “In some cases we have taken remedial action, restricting the times of day the arrows will flash or in some case shutting them down completely.”

Two locations Poch used as examples were the intersections of Eastgate Way and Richards Road, and Eastgate Way and 150th Avenue Southeast. Both intersections had protected-permissive lights until the number of collisions necessitated a change.

Poch said each flashing yellow light cost the city between $2,500 and $5,000 to install per intersection. With nearly 100 flashing yellow arrows, he estimated the total rolling cost to install them has been around $250,000 total.

While the data collected by the city provides a valuable look into the efficacy of protected-permissive lights around Bellevue, Poch admits it leaves a lot to be desired.

The data is sourced from Bellevue Police collision reports, so left-turn accidents all fall under one category.

“Most, maybe 90 percent of the collisions happen at traffic signals,” Poch said. “But not all of them.”

Also not included is the possibility of speeding, inebriation or human error. It’s hard to tell what the major cause of collisions at the pro-per lights is, Poch said. “Close calls” are not accounted for.

Poch said the biggest factor in installing a pro-per light was sight distance for the left-turning vehicle, but speed of oncoming traffic, variable traffic volume at different hours of the day and number of lanes to be crossed all came into play.

While more study goes into the lights and the city adjusts for traffic volume, the lights continue to be installed and some drivers in Bellevue continue to be wary — fairly or unfairly.


Ryan Murray: 425-453-4602;


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