A Petaluma man was arrested Sunday morning on suspicion of driving under the influence of alcohol, his third DUI in 10 years, Petaluma police said.

An off-duty Petaluma firefighter spotted Narcisco Roman, 43, swerving and driving on the shoulder of the roadway on Petaluma Boulevard North near Stony Point Road at about 7 a.m., police said.

The firefighter followed Roman’s white hatchback and called emergency dispatchers to provide the license plate number.

When officers located Roman’s vehicle and pulled him over, they found an open container of alcohol in the car, police said. Roman showed signs of intoxication and was arrested after he was given a sobriety test, police said.

He was booked into Sonoma County Jail on suspicion of DUI and his bail was set at $50,000.