Federal speed limit would be set in ECMs

Controversy surrounds proposals to place limits on truck road speeds and always has. Yours truly worked his way through college in the early 1960s by driving newspaper delivery trucks.

Those running highway routes had speed recorders – anybody remember the Sangamo Tachograph, in which a speedometer-driven needle scribed a line on a circular paper graph? In those pre-freeway days, the company’s speed limit was 50 mph, but managers allowed us to go 52 mph. And that’s where a squiggly line was drawn on every “tach” graph that sat on the shop foreman’s desk.

We suspected that no one actually reviewed them, but they might. And they’d surely be looked at if we got into a wreck, so we stuck to the unofficial speed limit. We didn’t like the “tachs” but as we got older (into our late teens and early 20s) and a little wiser, we grudgingly understood that they sometimes kept us out of trouble.

Physically keeping a truck within a limit was once done by mechanical governors, but they could easily be tampered with and defeated by savvy drivers. Since the advent of electronically controlled engines, speeds can be set in the electronic control module, or ECM. Whatever the method, calls for limiting the road speed of big trucks have risen and fallen over the years.

Today, the issue is again before the trucking industry and its professional drivers as federal authorities consider mandating speed limiters.

No speed has been specified in the notice. At this writing, FMCSA is taking comments and is no doubt getting a lot of them – among them, maybe from you.

“Speed limiters have been around for quite a while,” noted Tom Cuthbertson, now retired from Omnitraks, a maker of tracking devices, who also worked for the old Rockwell Automotive (now Meritor), maker of the old Tripmaster recorder. “It’s now done through the engine (engine control module), where owners can set various speeds, sometimes with tolerances to allow for traffic movements. There can be timing delays, which allow certain periods of traveling above a certain set road speed, and tolerances for going downhill. When time limits are exceeded or close to it, they give a warning to the driver.

“They’re password protected so they can’t be monkeyed with. There are reporting standards to show if someone has tried to tamper with it. The fleets implement them on their own trucks but don’t try to tell owner-operators what to do. Limits are set with software through a tool or over the air with password protection.”

Passwords can be combinations of letters and numbers, explained Bill Brown. He’s retired from Southeastern Freight Lines, a less-than-truckload carrier that sets limits on its trucks and, like Cuthbertson, has been an active member of ATA’s Technology & Maintenance Council and involved in the speed limiter issue.

“It’s not static,” he said of a typical password, “and there’s one for every vehicle. It requires a third party to touch a vehicle with an identifier number – say, 99, followed by the last four digits of the VIN, plus numbers on the license plate. We don’t want our vehicles to be accessible to hacking. Somebody who’s driving alongside can see the license plate numbers, but can’t know the others.”

Hacking is a big threat, and cybersecurity in general is a matter taken seriously by the industry, he said.

A modern engine ECM control module can measure road speed by counting wheel revolutions as the truck goes down the road, usually through the sensors in the antilock braking system, Brown explained.

That will vary with wheel and tire size, so the fleet has to determine how many revolutions are made in a mile at the desired set speed, say, 65 mph. As tires wear they get slightly smaller, so the number of wheel revs increases. That can be compensated for by slightly raising the allowable number of revs. Southeastern also puts limits on engine revs in each transmission gear, encouraging drivers to up- or downshift at proper times to save fuel.

Electronics are sophisticated, but sharp drivers have been known to defeat speed limiters. Brown said he learned of a driver who regularly cruised at 80 mph, “but he was turned in by other drivers who were jealous because they couldn’t go that fast. I suggested to the company that they keep him on if he would tell me how he did it. But (human resources) overruled me, and he was terminated,” and the secret went with him.

Does a federal speed limit make sense?

“I’m not going to take a side,” Cuthbertson said. “I see what’s good with it, but can see why people would oppose it. And how can you set one that makes sense? (A speed limit) on I-95 is anywhere from 70 to 55 in Virginia – 55 in Alexandria, then up to 70 as you go south, then down again at Richmond, then higher beyond. What speed should it be set at? I couldn’t even guess. Some fleets set them at 68, so they can handle the 65s and 70s. Trucks running at 55 can cause issues” with other traffic.

Speed limiters don’t help in a lot of cases, Brown said.

“What value is there for any speed limit if the posted limit is substantially lower? A truck could still travel 65 in a 35,” Brown said. LL