Route 12 from 5 to Petaluma

I agree with taking I80 to Vallejo but I recommend turning off 37 onto Lakeville highway which will allow entering 101 at the south end of Petaluma. Nice 2 lane road, a little shorted route and you will skip a bunch of traffic.

Sandra wrote:
How is route 12 with a 36' rig towing car?

No problem east of I-80. A bit bumpy at times but an easy tow. When you get to Suisun City/Fairfield on SR-12 you will merge onto I-80. I recommend you stay on I-80 westbound to Vallejo then exit at SR-37 (6 Flags) and take SR-37 West to U.S. 101 North. SR-12 west of I-80 is curvy. If you are going to the KOA the map programs may tell you to take SR-12/SR-121 to Arnold Drive to Frates Rd to U.S. 101. Nice drive in a car. Lots of lost tourists who will cause you to be on your brakes often. 12 to 80 to 37 to 101 is far less stressful.