How fast was he driving when he hit the girl on the sidewalk? He’s dead now after falling asleep at the wheel, hitting the girl then hitting a pole. So’s the girl after sliding several metres in the grass. Speed is important in reconstructing an accident like this.
His speed can be assessed from the damage to his car. It’s called a “crush” analysis, not surprisingly. The assessment can be cross-checked with a different analysis using data from the skid marks of the girl in the grass.
Experts in accident investigation like to cross-check assessments like these – and also refine the analytical methods with new data. Some of the methods are rough and seemingly not very scientific but that’s hands-on engineering and better than nothing. If you can measure something – e.g., skid marks, crush shape - even approximately, you can “manage” it; in this case get the speed of the car.
That’s what I was doing last week at a meeting in Moncton of CATAIR, taking part with about eight others collecting data for the continued refinement of an analytical technique. This time using the skid marks of a body in the grass for determining the speed of a vehicle during an accident. It sounds complicated but a lot of it boils down to determining the coefficient of friction of a surface like in simple high school physics.
With enough testing, chaps like Mike Reade, Moncton hope results will benefit investigators in situations when they only know the pedestrian’s sliding/tumbling distance after an accident. The results will be shared with others who work in this field. (Refs 1, 2)
In this case, Mike, who was directing the research and will crunch the data later, threw Skippy, a full size dummy, from a speeding pickup truck driven by Ken Zwicker, Bridgewater. The rest of us carried out various tasks like spotting where Skippy hit the ground, measuring how far he slid and videotaping what happened to him after he was “hit” by the truck. Katelynn Everett, a consulting professional engineer from Fredericton, recorded data and did preliminary number crunching.
The field trials are part of the very impressive, ongoing work by CATAIR, the Canadian Association of Technical Accident Investigators and Reconstructionists, and others to refine the analytical methods used by traffic accident investigators. (Refs 2 to 7)
The association is a mix of serving and former RCMP and municipal police officers, professional engineers and technologists all of whom are interested in traffic accident investigation and reconstruction.
In the morning before starting the field trials we met and discussed about 12 different courses on topics related to traffic accident investigation that are available to CATAIR members.
CATAIR meets somewhere in the Atlantic provinces about three or four times a year and do field tests most times. Recently three teams measured the crushed shape of three different cars that had been involved in traffic accidents. Each team is analysing speed using different methods and comparing results – Stu Smith, Dartmouth gave a brief report at the meeting on his work on this. Another time the stopping distance of a vehicle on a road was measured. And another time still, the turning radius and the path of the rear wheels of a school bus were measured.
Nobody gets paid for this field research. It’s all to do with refining our understanding of the cause of traffic accidents and reconstructing these, and the camaraderie of like-minded people working together – we do have fun when we’re getting our hands dirty and mud on our boots.
- Reade, M. W. (Mike), Personal communication. June, 2017
- Reade, M. W. (Mike) and Becker, T. L. (Tony), Fundamentals of Pedestrian/Cyclist Traffic Crash Reconstruction, Institute of Police Technology and Management (IPTM), Jacksonville, FL 2016
- Civil litigation, forensic engineering and motor vehicle accident reconstruction. Published September 22, 2015
- Is your traffic accident investigator well trained, experienced and “accredited”? Published February 23, 2016
- “Seeing is believing” at a meeting of traffic accident investigators. Published March 4, 2016
- If you can measure it you can manage it, even if it’s a real mess like a car or truck accident. Published June 23,, 2016
- Forensic assessment of traffic accidents. Published October 26, 2016