The southbound Truck tunnel on Interstate 5 reopened Thursday, a month after a fiery crash killed three people and temporarily shut down the West Coast’s main commercial route.

The tunnel reopened 15 days earlier than expected, said Officer Patrick Kimball of the California Highway Patrol. Authorities initially warned that repair work could take months.

The contractor, Security Paving of Oxnard, will earn a $2.9 million bonus for completing the repairs in less than 33 days, Caltrans officials said. The work included replacement of slabs, concrete barriers and a metal guardrail.

Authorities determined that 31 vehicles — including Big rigs and one passenger vehicle — were involved in the Oct. 12 crash.

Several Trucks burst into flames and the fire spread from vehicle to vehicle. Flames shot nearly 100 feet in the air outside the tunnel and reached temperatures as high as 1,400 degrees.

The non-truck lanes reopened the day after the crash after engineers determined there was no major structural damage, and the northbound lanes followed soon after.

Truckers use I-5, the main West Coast interstate linking Mexico and Canada, to haul produce from the Central Valley to Southern California and to move goods from the ports of Los Angeles and Long Beach.