“Taking the measure” – forming an opinion, of the cause of a fatal motor vehicle accident

You can sometimes use a camera to take the measure of important technical issues during a forensic investigation.  And unexpectedly get the answers to your questions quickly and easily as I found out during one investigation.

I was retained by the RCMP a few years ago to determine if a pile of salt on a highway contributed to a fatal motor vehicle accident (MVA) – that was the technical issue.  I did this by carrying out field trials like they do in speed bump research.  These trials determine the effect of different sizes and shapes of speed bump on vehicles travelling at different speeds.

When I started these trials I didn’t know where they would take me except they approximated what took place during the fatal MVA – and involved measuring like engineers do.  There were no neat little formulae, no salt-pile-contribution-determining procedures in text books.  But I had to start somewhere – the way it so often is in forensic engineering investigation.  The end result was surprising in answering the question about the contribution of the salt pile.

I built a test site on a run way at the Shearwater airport like those for speed bump research.  I marked off a traffic lane on the runway the same size as that at the accident scene.by painting a centre line and shoulder lines.  I then constructed a pile of salt in the lane the same shape and size as that at the scene.  My tests would involve driving the vehicle in this lane, over the pile of salt and filming what happens – the effect.

Speed bump research records what happens to a vehicle at a speed bump by measuring and photographing its position in three dimensions:

  • Side to side in the traffic lane between the centre and shoulder lines,
  • Along the lane with a large ruler, and,
  • Vertically above the lane with another large ruler.

I did the same at my test site.  The painted traffic lines oriented the vehicle side to side in the lane.  A large ruler consisting of 1.0 foot graduations painted on the asphalt down the lane from the salt pile located the vehicle in that direction.  Another ruler consisting of 0.5 graduations marked on a sheet of plywood set at the side of the lane opposite the salt pile located the vehicle vertically.

I retained three professional photographers to film the position of the vehicle as I drove over the pile of salt.

  • One was in the cab with me to film what I saw and experienced.
  • Another was in the bucket of a boom truck down lane and 50 feet above filming the position of the vehicle side to side in the lane.
  • The third was off to the side of the pile of salt filming the position of the vehicle against the backdrop of the rulers painted on the plywood and on the lane.

I also staged the position of the vehicle on the salt pile and had this filmed from a sea king helicopter for illustrative purposes – you would use a drone fitted with a camera to get these pictures today.  The photographer with his camera is shown above in my blog site masthead.

The RCMP told me that the vehicle was travelling at a speed of 50 km/hr or more when it hit the pile of salt.  This was based on tests by their accident reconstruction specialist.  I planned to do my test at that speed but start at the lower speed of 20 km/hr and gradually increase.

I drove the vehicle over the pile of salt at 20 km/hr as the cameras rolled.  It was pretty well all I could do to keep the vehicle in the lane after striking the pile of salt – it did veer off to the right a little and this was captured by the camera man in the boom truck.  Striking is an apt term.  And it was all the camera man in the cab with me could do to keep his camera steady as the vehicle rocked and rolled.

We saw on viewing film of the vehicle against the backdrop of the big rulers that the vehicle got 2.0 feet of air on striking the pile of salt and the front wheels stayed aloft for 18 feet before landing on the test lane again.

The three cameras recorded about 30 minutes of film.  I viewed this film and edited it to a four minute film clip to include in a preliminary report to the RCMP.  I reported that I could not continue the testing at higher speeds until I had safety and rescue procedures in place for the driver.

The RCMP and counsel on viewing the film clip and learning of my need for safety measures stopped all further testing.  ”No need to continue testing, we have our answer”.

They quickly saw in the film clip the effect, the contribution of the pile of salt to the erratic behaviour of the vehicle and its airborne trajectory at 20 km/hr.  It didn’t take much imagination to know how the pile of salt would contribute to a fatal MVA at a speed of 50 km/hr.  Seeing is believing when you’re taking the measure of some things.  That’s often more than good enough for the justice system.

But all of this was also quantified by filming and recording the 2.0 foot and 18 foot airborne measurements and the veering of the vehicle off to the side of the traffic lane.


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