Background
In the middle of the night, a fully loaded tractor-trailer collided with the side a 40 foot bus about four kilometres north of Gibbons, Alberta. Prior to this collision, the bus had become stuck across the road when it attempted to turn around on a two-lane highway after an earlier collision had closed down the highway.
Police had been investigating the earlier collision but a cruiser re-directing traffic at the north end of the scene had moved from its post allowing unimpeded travel toward the bus. The driver of the tractor-trailer was charged with six counts of dangerous driving causing death and 19 counts of dangerous driving causing bodily harm.
Analysis
We were retained on behalf of the truck driver and the trucking company to investigate and reconstruct the accident. The position of the bus at the time of impact was reconstructed from scrape and tire marks on the roadway and a gouge beside the road. Our analysis (see diagram below) showed that approximately 40 percent of the bus was off the roadway with the rear of the bus angled down roughly 4 degrees.
Our speed analysis found that the tractor-trailer was travelling close to 90 km/h where the speed limit was 100 km/h. This was consistent with the reported evidence and the results of a speed analysis by another expert on the case.
As part of the avoidance analysis, we conducted a nighttime re-enactment at the site close to the three year anniversary date of the accident. An exemplar bus and tractor were obtained for the re-enactment and the highway was closed off by the police. The tractor was driven at 90 km/h toward the bus that was placed across the road. A test subject inside the tractor used a Vbox III to record the location when lights were first visible, when a silhouette first appeared and when the side of the bus became visible.
The images below, captured from a video taken during the re-enactment, show that the lights from the town of Gibbons (with the tractor 2.5 kilometres from the bus) provide a very similar view to the lights on the side of the bus (350 metres away). This illustrates how difficult pattern recognition of lights can be in some cases.
Results
In her Reasons for Judgement, Madam Justice Smith found on all of the evidence, the better re-enactment was the one done by the defence. It most closely approximated the actual event. The driver of the tractor-trailer was acquitted of all charges.