In an effort to reduce one of the leading causes of automobile collisions in Petaluma, the city will soon begin modifying traffic signals at 26 intersections around town to restrict when drivers can turn left.
The intersections to be targeted currently allow drivers to make a "permissive" left turn on a solid green light. Permissive signals let drivers turn left on a regular green light — without the protection of a green arrow that indicates all other traffic is stopped — so long as they yield to oncoming traffic.
An example of this kind of signal is at East Washington Street and Lakeville Street, which saw the most accidents of any intersection in town in 2011 and 2012.
These types of signals tend to lead to right-of-way collisions, where a driver fails to yield properly to another vehicle.
The move to change the signals comes after officials found that the top cause of local collisions in 2010 was right-of-way violations, many of them taking place at intersections which allow left turns on green lights. In 2012, right-of-way violations remained the second highest cause of car accidents behind speeding.
"People try to squeeze through (in front of another car), get distracted, or don't see an oncoming car," said Petaluma Police Sgt. Ken Savano, explaining why more accidents occur at these intersections.
Indeed, a study by the Police Department and UC Berkeley Institute of Transportation Studies found that this type of signal "opens the possibility for a driver to make last minute decisions that can cause an accident," and recommended changes to all such intersections. In some cases, this will mean installing a new style of signal, one that includes a flashing yellow arrow. The flashing yellow arrow, according to city staff, has been shown to help drivers distinguish between the protected turn phase, when they can safely turn left on a green arrow without worrying about oncoming traffic, and the permissive phase, when they must yield.
Petaluma will be only the second city in the county to use this new technology; Santa Rosa implemented the flashing signals in January.
Other intersections will be modified to allow left-hand turns only on a green arrow.
In 2010, the city received a $441,000 federal grant to make changes to the signals, and it is now preparing to send the project out to bid.