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RCMP takes to the track to test truck accident dynamics

HANNA, Alta. - Talk about getting cold, hard data.


HANNA, Alta. –Talk about getting cold, hard data.

It was an unseasonably chilly and stormy week in rural Alberta when representatives from police services, government and the transportation industry converged on an isolated test track to put a selection of big rigs through their paces in the interest of science and safety.

The miserable weather didn’t dampen the enthusiasm of the participants, however, who came from a variety of locations in Canada and the US to either help with or observe a series of tests designed mostly to glean data that can be used in collision reconstruction.

That’s how the sessions were envisioned by the RCMP officers who spearheaded the tests and, according to Sgt. Sam Hewson, the RCMP’s Edmonton-based collision reconstruction program manager for K Division, it went very well. “We’re very happy,” he says. “We conducted 49 skid tests and also did timed acceleration tests.”

Hewson describes the latter tests as measurements from a truck’s starting point to a second point 50 metres down the track.

“One of the guys was there with a stop watch and he timed how long it took them to get to the 50 metre point,” he says of the measurements, which were designed to get a general idea about acceleration rates.

Unlike a drag race, however, he says, “It wasn’t like they were generally jumping on the accelerator, they’d just start out and drive forward.”

Perhaps it was only to the drivers involved that the acceleration tests seemed like a drag, then…

The multi-day event also saw some tests involving more mainstream vehicles.

“We conducted a couple of skid tests with a pick-up truck to get baseline coefficient of friction for the track surface,” Hewson reports. “Which gives us the slowing rate for a passenger vehicle or a pick-up truck and we’d compare that to what a rig does. It’s a benchmark, essentially.”

The RCMP, which was joined by members of city police services from Calgary and Winnipeg, wanted the data because one of the things they do after a collision involving a rig is to make a note of the braking tire marks left at the scene. Using that information, Hewson says, investigators can determine a minimum speed loss over the braking distance, “so we can say, for example, that the trailer unit lost 50 km/h over the distance it was braking.”

When you lock up a rig’s brakes on pavement and slide to a stop, the RCMP sergeant reports, you’ll typically get 65% of a car’s braking efficiency on the same surface.

“That’s a starting point,” he says. It helps them determine factors such as speed at impact. “If all the brakes appear to be working,” Hewson says, “it’s a panic stop situation and we’ll give them a percentage of braking efficiency versus the direct factor of the coefficient of friction of the road surface.”

Hewson says they also did friction testing of various tire setups, standard trailers versus mixed axle groups and new versus worn tires. They also looked at dual wheel configurations compared with ones running the Michelin X One single tires.

Like a prize fight, the tests were preceded by a weigh-in.

“We weighed the trailers, measured their dimensions, wheel bases, and the like,” says Hewson. “And then we conducted braking tests with units loaded and unloaded, air in the suspension, no air in the suspension system.”

Hewson says the idea for the test sessions began with Lethbridge’s Corporal Barry Rediron, RCMP forensic collisions reconstructionist for Southern Alberta. Rediron wanted to roll some semi-trailers to figure out their rollover value.

“We were thinking the rollover thing might be hard to do,” Hewson says. “But after one of the members from Calgary mentioned he goes to collisions involving mixed axle group trailers, lift-axles, and so on, we decided to go that route.”

The concept of testing lift-axle trailers for braking efficiencies came about, Hewson says, “because we didn’t know of any other data out there. So we found owners who were willing to provide us with trailers and Michelin to provide the tires -because we’d be wrecking a lot of tires -and it went forward from there.”

The tests used four different trailers in three tandem Super-B configurations from two different manufacturers.

“We’d skid them to see what they have,” Hewson says. “And then lift up the axles and skid them again.” Hewson acknowledges that he doesn’t expect people will run raised lift-axles loaded, like they did in the test, but they did it anyway and discovered that it definitely increased the stopping distance.

Braking distances were calculated in part by using “shot markers,” devices mounted on the front of the trucks that would fire a .22 calibre power load, similar to what would be used for driving concrete nails, when the brakes were applied.

“You break off a piece of chalk into the cylinder and it fires that chalk into the ground at the point where you apply the brakes to give you the starting point for the braking,” Hewson explains.

That starting point can depend on a variety of factors, including the shot marker’s height from the ground and the speed the truck is travelling, but for the purposes of these tests, Hewson says, it was close enough.

From that point, “If they skid to a stop and stay stopped,” Hewson says (noting that sometimes the driver would forget to stay put and start to drive away, wrecking that particular attempt), “we’d measure the distance from the chalk mark to the device that fired it at the point at which it finally stopped -and that’s your braking distance.”

They used radar to gauge the speed of the vehicle at the time the brakes were applied and plugged that into a simple formula to determine braking efficiency.

“This is grade 11 physics,” Hewson says. he admits the tests may not be unique, but says it doesn’t matter.

“The more testing you can do the more value you get out of it,” he says. “We look at this as a start. Forty-nine tests is a lot, so we got a lot done, but when you’re dealing with data you want more numbers, a larger volume of test data to make your numbers solid, to make sure the data is consistent.”

While the foul weather that added so much tribulation to this September’s trials gave insight into how the vehicles performed under one particular set of conditions, plenty of other parameters could be changed in subsequent test sessions, including the surface condition of the track and different braking systems for the trucks and trailers.

“We didn’t compare ABS with conventional braking, for example,” Hewson says.

The big advantage with ABS is that it stops straight.

“When you’re talking about a Btrain,” Hewson says, “such an articulated vehicle has two bend points, and if you push it from behind it’s going to accordion on you like a snake.”

Since ABS brakes let you brake in a straight line, however, with no risk of the jackknifing that’s possible with conventional brakes, the driver maintains steering control.

While the weather chose not to cooperate, the track did its job well.

“It’s a good facility,” Hewson says of the 3.5-km oval. He notes that its isolation was a double-edged sword, though. “You don’t have issues with interference from traffic,” he says, “but it’s harder to get to. For what we did it was great, though. We weren’t on a public road so it was safe, and we didn’t have to dodge traffic or block off a road -let alone get permission to close down a road -so it was awesome.”

It’s also very narrow, laid out as a single lane for most of its circumference, but that didn’t hurt these particular tests.

“We’re not doing anything that involves width,” Hewson says. “So for our purposes it works very well.”

The next step is to take the raw data and present it in a way that people who weren’t there can understand.

“There’s some talk about producing a paper for the Society of Automotive Engineers,” Hewson says, “and I know a lot of the industry people are interested in it becau
se it affects how their systems work, how efficient they are.”

Hewson tips his Mountie hat to all of the people who braved the conditions to take part. “There were a lot of people from the trucking industry who came out and gave us a huge hand,” he says. “We couldn’t have done it without the volunteers, rigs, the tires, the drivers.”

While the results are in, it’s going to take time before the inevitable reports can be written.

“We have not properly analyzed the data yet,” Hewson says, “but the braking distances of the properly set up and functioning lift-axle trailers we tested appear consistent with what we expect to see on our roads.”

Hewson says they’ve also shared the preliminary compilation of data with Alberta Transportation and with Transport Canada and will be sharing all the data with them once it is organized.

How did Michelin’s X One tires work out? “Good,” Hewson says. “We haven’t crunched the numbers yet but I don’t see any huge differences there. It’s too early for any conclusions, though.”

It’s Hewson’s hope the industry can use the information to make improvements to their products or techniques, or just to be assured that what they’re doing works. “We aren’t treating this as proprietary.”


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