OTTAWA -- A collision reconstruction expert says the glare of the sun and improperly covered construction lines were likely a factor in the 2019 fatal OC Transpo bus crash at Westboro station.

The defence continued to build its case at the trial on Thursday, alleging Aissatou Diallo is not responsible for the fatal crash.

Collision reconstruction expert Richard Lamoureux presented to the court key findings of his report. 

"Sun glare and an improperly obliterated construction line were likely factors in the collision," Lamoureux testified.

Both issues have been repeatedly disputed by both sides in the trial so far.

Lamoureux also told court, "After the bus veered off the road, the driver attempted to steer the bus back onto the road."

He testified the bus was not responsive to the steering due to "slip", a type of skid — though not cause by any mechanical issues.

"The subject accident involved a series of collisions occurring within a second or two of each other, such that the driver likely did not have time to perceive and react to one situation before the next occurred," Lamoureux also told the court.

Throughout the trial, the Crown has laid out its evidence alleging more could have been done to avoid the collision.

In cross-examination of this latest witness, the Crown challenged the expert’s assessment of how fast the bus was travelling and whether the driver applied the brake.

Three people died and dozens were hurt in the 2019 crash.

Diallo has pleaded not guilty to three counts of dangerous driving causing death and 35 counts of dangerous driving causing bodily harm.

Closing arguments in the trial by judge alone are expected next week.