The signal at a crossing over the Sonoma-Marin Area Rail Transit tracks on Rohnert Park Expressway malfunctioned at midday Monday, blocking traffic temporarily for at least the second time in a week.
The road was blocked for about 35 minutes shortly before noon, the agency said.
Spokeswoman Carolyn Glendening said it is not clear yet why the gates malfunctioned, but traffic flow was fully restored by around noon. The contractor that monitors the crossing gates, Willits-based Summit Signal Inc., sent a nearby worker to reset the mechanism.
The same gate malfunctioned on May 1 as well, stopping traffic for about 45 minutes on the busy east-west road during the evening rush hour. That failure was caused by a faulty computer card, Glendening said.
In Monday's case, the gates came down when a train carrying equipment passed by, Glendening said, but the gates failed to open up after it passed.
The crossing is among those that have been renovated in anticipation of the start of commuter rail service along the North Coast by late 2015 or early 2016.
There have been a scattering of gate failures along the line in the past year, including at least one in Santa Rosa in November and several in Petaluma in December. In many cases, investigators found the crossing gates had been vandalized.
Glendening said the gates are designed to close if there is any kind of problem in the control system: It is safer to have the crossing closed than risk having a train cross through traffic unannounced.
Rohnert Park Police Sgt. Aaron Johnson said Monday's closure wasn't particularly disruptive, but the city is concerned that the crossing be reliable in the fall, when Graton Resort and Casino opens.
Motorists stuck behind closed gates at that location had few options: The gate system is too narrow to bypass and there is a median strip blocking cars from makine a u-turn, Johnson said. Attempting to do either maneuver is dangerous and is in violation of state law.
"If they would just stay put, in a short period of time, the gate will be lifted and they will be on their way," he said.
Although the commuter rail service is still years away, the tracks are in use now by freight and utility trains, she said.