Canada's Transportation Safety Board has announced a full "Class 3" investigation into how two CP Rail freight trains crashed and derailed while one was trying to pass the other early Sunday high in the B.C. mountains just east of the Rogers Pass.

A CP Rail conductor on eastbound train 602 suffered a concussion around 2:25 a.m. PT when he was thrown from his seat, while the engineer at the controls escaped serious physical injury when their locomotive, hauling empty potash cars, slammed into the tail end of a parked westbound train.

It happened at Beavermouth, along CP's Mountain Subdivision running between Golden and Revelstoke.

"At this point we are not drawing any conclusions. We're still gathering information to conduct the investigation," safety board spokesman Chris Krepski told CBC News.

"In this case, we're examining train handling, the track infrastructure, mechanical aspects with respect to the locomotive and the rail car and the signal indications."

Safety board examines 'over length' train

Sources familiar with the incident tell CBC News the parked, westbound train 113 was carrying tall, double stacked intermodal freight cars and had pulled onto a side track, or siding.

But sources said it was "over-length," meaning it was too long to fit entirely on the side track and had several rail cars trailing out on the main track.

CP Rail's Mountain Subdivision through B.C.'s Rogers Pass is one of Canada's steepest, most dangerous railway corridors. (Dave Seglins / CBC)

On the approach to the siding at Beavermouth, several sources said, the eastbound train passed a signal indicating the crew should be prepared to stop ahead. But for some reason, the eastbound train rounded a corner, passed the first section of train 113 parked on the siding, and then failed to heed the stop signal in time and slammed into 113's back end.

Two front-end locomotives of train 602 derailed, along with an empty potash car. A single car of the parked westbound train was forced off the track.

The length of the trains, and the communication between the crew and CP's rail traffic controllers, will be central in the investigation.

"Because we have two trains operating on the same track, obviously we are going to look at the procedures and safety defences in place to see if there's any breakdowns there," the Transportation Safety Board's Krepski said. "Length of the train,... whether the train was the appropriate length for the siding."

Not uncommon

"Over-length" trains are not uncommon on CP Rail's main east-west corridor. Oncoming trains are able to pass one another if the shorter train stops adjacent to a siding, to allow the longer train to then snake around using the side track as a passing lane.

But in 2009, CP Rail suffered a similar side collision of two trains involving one which was over-length. It happened at Redgrave, just eight kilometres east of Sunday's crash site.

In that case, the safety board concluded the crew of the oncoming train was distracted, failed to appreciate the train ahead was "over-length" and partially blocking the main track, and ultimately failed to heed the signal warning them to stop.

The safety board interviewed the crew of CP train 602 on Sunday and will begin downloading and deciphering the locomotive event recorder to determine how fast the train was travelling when it first applied its brakes.

The results of the investigation are not expected for many months.

Please send tips on this story to dave.seglins@cbc.ca.