Santa Rosa traffic engineers are hoping a new kind of traffic signal will help drivers make better decisions when they make left turns at intersections in the city.

The city is the first in Sonoma County to install traffic signals with flashing yellow left-turn arrows.

While they may take some getting used to for drivers, engineers hope the new signals will reduce vehicle collisions by making it clearer that such turns need to be taken with care at intersections.

"These have been pretty successful in all the before-and-after studies that we've seen," said Bill Ellis, a city traffic analyst.

The new signals are being installed around the nation, following the lead of the Federal Highway Administration, which began allowing them a few years ago.

The first signal is going in at North Dutton Avenue and West Ninth Street. Engineers installed them Wednesday, but a software glitch prevented them from working properly.

"We had a little setback, but we'll get it running," said Traffic Engineer Rob Sprinkle, who said they will try again next week.

The intersection was selected for the first signals because it has an unusually high number of traffic accidents attributed to right-of-way confusion, Ellis said.

"People are getting into a similar type of collision out there consistently," Ellis said. "Year after year after year, we have the same things going on."

From 2004 to 2008, there were 51 traffic collisions at the intersection, 16 of them right-of-way accidents involving vehicles traveling north or south on North Dutton, he said.

Currently, drivers turning left from North Dutton onto West Ninth face what is known as a protected-permissive left-turn signal. A driver is first given a green left-turn arrow that gives them the right of way, thus "protecting" them from oncoming traffic.

But after a few seconds, the arrow turns off, switching to the regular "permissive" green light. This allows drivers to continue trying to turn left when there is a safe gap in oncoming traffic.

But that's where some drivers are getting their signals crossed.

Something about this pattern is apparently too "subtle" for some drivers, causing them to be confused about the difference between the green arrow and the regular green light, Ellis said.

But the new cycle should be far clearer, Ellis said.

Following the solid green arrow, a yellow arrow is displayed warning drivers that the protected phase is coming to an end. Then the signal will turn red briefly, before switching to the flashing yellow left-turn arrow.

This tells drivers that it is OK to turn left cautiously as long as there are no oncoming vehicles or pedestrians in the area.

The flashing yellow arrow will then switch to the solid yellow before the signal turns red again.

The other option to improve safety at the intersection is to simply not allow left turns on anything but a green arrow. But then cars might be sitting at the intersection longer than necessary for the conditions, Ellis said.

"This seems like a good way to improve efficiency and improve the safety of that location," he said.

The city will monitor the intersection before deciding what other intersections should try the new signals, which cost about $4,500 per intersection to install.

You can reach Staff Writer Kevin McCallum at 521-5207 or kevin.mccallum@pressdemocrat.com. OnTwitter @citybeater.