Capt. Tracey Stuart said notes found at 53-year-old Thomas Robinson's home and witnesses' statements about his driving before the collision indicate he likely intended suicide.
"He was driving fine until he abruptly turned into the path of the truck," Stuart said this morning.
An autopsy showed Robinson died of blunt force trauma injuries, Stuart said.
Robinson was driving a 1977 Ford Escort west on state Highway 12 near American Canyon just west of the Solano County line when he crossed over the double-yellow line and drove into the path of the oncoming 2000 Mack tractor-trailer.
Two other vehicles were involved in the 10:30 a.m. crash, which sent eight people to hospitals with minor to moderate injuries and closed the highway for eight hours. Seven of those injured were in a Toyota Sienna minivan.
The big-rig was hauling a bulldozer back to Siskiyou County after it had been brought to Napa County as backup equipment for two vegetation fires over the weekend, Cal Fire Division Chief David Shew said.