As many as 51 people have been injured, including 4 who are critical, when a commuter train from Metrolink crashed into a tractor-trailer Tuesday morning. The semi was on the railroad tracks in Ventura County, which is northwest of Los Angeles. One of the critically injured was the train engineer.

Sergeant Denise Shadinger from the Oxnard Police Department said the collision was first reported at 5:44 a.m. She said the truck was fully engulfed in flames shortly after the collision.

Authorities at a news conference following the accident said many victims had been treated for extremity and head injuries. The commuter train, which has 79 miles per hour cruising speed was traveling much slower at impact, said one official.

Sergio Martinez the Battalion Chief for the Oxnard Fire Department said the train’s conductor noticed the vehicle early and was able to established his emergency protocol.

The train at the time of the accident had 51 passengers on board and was en route to Los Angeles from Ventura County.

There is a stretch of track about 65 miles away from Los Angeles where the accident took place and because the land is flat, the conductor could see the vehicle and was able to start braking in advance.

The tractor-trailer driver survived the collision but fled the scene. He was later apprehended within a mile from the scene of the crash said officials.

Three of the train’s passenger cars were toppled by the collision and a fourth was derailed but remained upright, as did the engine.

After the fire was extinguished, there was little that remained of the tractor-trailer. Emergency vehicles were scattered around the area where victims were being treated, while others were wheeled away on stretchers.

A train that traveled on this same route back in 2008 was also involved in a crash killing 25 and injuring another 135.

A team of investigators was being dispatched to the site of the crash by the National Transportation Safety Board.