A car plunged down an embankment off westbound state Highway 4 in Martinez Friday morning, slamming into a tree and killing the driver, the California Highway Patrol said.
The left-hand lane on the Alhambra Avenue off-ramp is partially shut down at present to recover the driver's car, according to the CHP.
The man was driving a black 1994 Honda Civic in the rain approaching the off-ramp when he veered from his lane off the roadway around 8:29 a.m., the CHP said.
The car sped down the embankment and hit the tree on the driver's side, crushing the driver, the sole occupant of the car, the CHP said.
CHP officers found the Walnut Creek man unresponsive and trapped in the car, according to the CHP.
The man was pronounced dead at the scene. The left lane on the off-ramp is partially shut down so workers can recover the Honda.
Anyone with information about the crash is asked to call the Contra Costa CHP at (925) 646-4980.