An investigation into a collision between a Via Rail train and an Ottawa city transit bus will look at a number of things, including the train's black box and witness statements, experts say.

Transportation Safety Board investigators and Ottawa police have spent the day at the scene of the crash near the Fallowfield train station, in the Ottawa surburb of Barrhaven, after a collision between the train and bus around 8:48 a.m. Wednesday.

The driver of the bus, Dave Woodard, was killed in the crash. Five others are dead and 34 injured.

The TSB now has 11 staff at the crash site, Jean Laporte, the TSB's chief operating officer said Wednesday afternoon.

A passenger train collision with so many victims is "Very rare," said Ian Naish, a former director of rail safety investigation at the TSB.

An investigation could take months or even more than a year, officials say. Here are five issues investigators will look at during their probe.

The black boxes

Lead TSB inspector Glen Pilon said the priority for the team was to get the "event recorder" so they'll know how fast the train and bus were going and when they braked.

Naish said investigators will walk around the site and get a sense of what happened. They also frequently recreate the conditions of a crash to see whether they can detect possible problems. A second OC Transpo double-decker bus was on-scene by mid-afternoon.

The train and bus will likely be examined at the TSB engineering lab at the Ottawa airport to see what the damage tells them, Naish said.

Shawn Pulley, a driver with OC Transpo who has driven the same route Woodard was on, told CBC News that he tries to avoid the double-decker buses like the one involved in the crash because they are heavy and hard to stop.

"I've never driven it with people on it, but I can tell you that bus is heavier empty than one of the regular 40- footers is loaded," he said. "It's the equivalent of a fully loaded cement truck." 

OC Transpo general manager John Manconi said the bus had passed all its safety inspections.

The driver

The investigators will speak to OC Transpo and look at Woodard's work/rest patterns over the past three days, Naish said.

"There are so many questions," he said.

"He should have been seeing the train lights ... but we don't know his state of mind, don't know if a passenger was distracting him or anything. It's very hard to tell right now and you just have to speculate and test things [as an investigator]."

Investigators will also look at what Woodard did in his off-time and whether he got enough rest, Naish said.

Some drivers and passengers told CBC News that Woodard was new on the route and may have only driven it for two weeks. Naish said he'd then want to know whether OC Transpo does test drives or coaching for drivers on new routes.

"Certainly it would be an issue to investigate ... there's lots of human factors here, I'm sure," he said.

Colleagues and friends say Woodard was a diligent, conscientious driver. 

Which vehicle collided with which?

Witnesses from the bus and train gave conflicting accounts of whether the bus hit the train or whether the train hit the bus.

Naish said the fact that the front of the bus was sheared off indicates it was hit by the train.

"Because if the bus had hit the side of the train, you wouldn't expect anything to shear, just to crumble," he said.

"There are quite a few crossing accidents where people see the train at the last minute and they stop and they come to rest on the track and then they get hit. They don't have to be right on top of the rails because there's an envelope around the rails that's occupied by the locomotive and the cars, because the rails are narrower than the train body."

He says it's curious that the train derailed when it hit the bus.

"It's sort of a glancing blow and the train's mass is probably at least 50 times the mass of the bus," Naish said. "Why did the train actually derail when it hit the vehicle?"

How soon investigators get answers to these questions will depend on whether the train or bus had a video recorder, he said.

Environment

The environmental factors could include driver distraction or whether the sun hit Woodard in a way that he couldn't see in front of him, Naish said.

Investigators will also look at how the train crossing was set up.

"You look at the way it's laid out, you look at the signal system, you look at the lenses, how clean they are," he said.

"The geometry of the intersection, not so good in my opinion. Not ideal anyway. But was it bad?"

Investigators will also look at the people who were injured or killed and where were they seated on the bus

Crossing concerns

Naish said he's driven on the road that runs parallel to the Transitway, Ottawa's dedicated bus road. The area is a busy intersection with a lot going on, between the street, the Transitway, a curve right before the crossing, and the rail crossing itself.

"As you approach the crossing, what you see is a field and trees. And you come around the curve, then you see the crossing, and then you see the signals and so forth," Naish said.

Pulley, the OC Transpo driver, said it's easy to see the train and that drivers have ample time to stop.

"It's very odd [Woodard] leaving Fallowfield station, seeing that there is a train coming, why he would be going that fast ... because you know when you're leaving the station there is no point in going fast coming up to the red light," Pulley said.

Ottawa police Chief Charles Bordeleau says there have been no collisions at that crossing since 2002, the earliest records available.