NAPA, Calif. -- A tour bus driver and five of his passengers sustained minor injuries when the bus was hit by a tractor-trailer in Solano County Thursday morning, a California Highway Patrol spokesman said.

The accident happened around 2:30 a.m. at the spot where the Columbus Parkway off-ramps from westbound Interstate Highway 80 and eastbound state Highway 37 intersect.

CHP Officer Marvin Williford said the driver of the big rig, Juan Velasquez, 30, of Williams, was taking the off-ramp from I-80 when the collision occurred.

Velasquez was unable to negotiate a sharp left turn at the bottom of the ramp and his 1993 Freightliner tractor-trailer entered the transition lane from eastbound state Highway 37 to Columbus Parkway, Williford said.

The big rig struck the 1997 tour bus, owned and operated by Reliant Travel of Oakland, in the transition lane and forced it onto the right shoulder, where the bus then struck several attenuator barrels and an abutment, the CHP reported.

The CHP identified the bus driver as Jimmy Duncan, 50, of Oakland.

A spokeswoman for Reliant Travel said Duncan was returning from the River Rock Casino in Geyserville and was taking the five passengers to Emeryville before returning to the bus yard.

The CHP reported that the injured parties were taken to Sutter Solano Hospital in Vallejo, but the Reliant Travel spokeswoman said Duncan and some of the passengers went to Kaiser Hospital on Vallejo.

The spokeswoman said Duncan has been with Reliant Travel for a "number of years" and has received letters of commendation for his driving record.

Alcohol is not suspected as a factor in the accident, which is still under investigation, Williford said.

The off-ramps were closed due to the crash, which also partially blocked one lane of Highway 37. The off-ramps and lane were reopened at about 5:35 a.m., according to CHP Officer Marc Johnston