Trains are doing test runs on the Northwestern Pacific in Sonoma County this week as the railroad gears up for freight service later this summer.

The California Highway Patrol advised motorists Friday to watch for the trains and obey signals at all railroad crossings.

"The train will be running slow through the area, but the CHP wants to remind everyone to obey all the railroad crossing arms, bells and lights," the Santa Rosa CHP office said.

"You will be cited if you cross the tracks while the crossing arms are active. Pedestrians are reminded to stay off the railroad tracks."

On Friday, an NWP Co. locomotive pulling two loaded rail cars was testing bridges between Napa Junction and Petaluma.

The railroad tests will continue, but commercial freight service isn't scheduled to resume on the Napa-to-Windsor segment until at least mid-July.