A road project on Point Reyes-Petaluma Road in Marin County will affect drivers and bicyclists this month.

Shoulder work, installation of drainage and repaving will be done starting at Nicasio Valley Road and then for a half mile east toward Petaluma.

The work is expected to begin by the week of Aug. 23 but could start next week.

A temporary traffic light system or flagger will be set up at Nicasio Valley Road and near Dolcini Dairy — which will depend on final approval by Marin County officials. If it’s the lights, the system will alternate traffic based on sensors, which will detect not only cars and trucks but also bicycles.

Dennis E. Zielke, project manager for Greener Excavations & Construction Inc., the contractor for the job, said it will be “extremely important that all bicyclists stop at and wait for the green light” during work hours. He said traffic will be routed single-file through the construction zone, and “anyone who does not stop and wait for a green will be facing oncoming traffic with virtually no run-off area.”

The work will be done 8 a.m. to 5 p.m. Monday through Friday and is expected to be done by Sept. 27.