About 500 drivers were screened during two Petaluma checkpoints this past Saturday night. The first was held on Sonoma Mountain Parkway near Rainier Circle between the hours of 6:00 p.m. and 9:30 p.m. A second checkpoint was held on Petaluma Boulevard South near Highway 101 between 10:30 p.m. and 2:00 a.m. One driver was arrested for an outstanding warrant for a previous DUI offense, driving on a suspended license and probation violation. Twenty drivers were cited or arrested for driving with no license or driving with a suspended or revoked license.