The state trooper was unhurt in the crash, but the two other drivers sustained injuries, said Trooper Russ Winger of the State Patrol.
The three vehicles collided at about 7:30 a.m. on Highway 101 near Cloquallam Road. The circumstances leading to the crash were not immediately known.
A detour was in place at the scene until the highway reopened at about 10 a.m.
The State Patrol says there also was a two-car accident on Highway 101 about a half-mile away at Shelton-Matlock Road.