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December 2, 2009 Vol. 5, No. 24

There’s no doubt in my mind, none at all, not even a tiny shred, that stability control systems of one sort or another should be mandated on tractor-trailers ASAP. I’d go further and include commercial trucks of all sorts, from light vans to cement mixers. Heck, why stop there? I want to see the technology mandated on all motorized vehicles, no matter the size, that travel on public roads.

And why wouldn’t we do it across the board? It’s plain to see that the various available technologies work a treat, and the cost per vehicle isn’t really very big at all. Especially not when you compare it to the cost of the mayhem that rollovers, jackknifes, and other loss-of-control accidents cause. This is no-brainer territory if ever I saw it.

Thankfully, it seems likely that we’ll soon get that mandate, on heavy trucks at least, after the publication of an important study south of the border by the National Highway Traffic Safety Administration (NHTSA).

At this point I’m sorely tempted to write something glib, like why spend millions on a study? They could have asked me. Being a motor noter, I’ve seen countless demonstrations of the technologies in question from their early iterations to the latest, played with them myself on dry, wet, snowy and even icy test tracks in North America and Europe. I’ve taken a tractor-trailer into an abrupt emergency-style lane change at 35 mph — on hard-packed, icy snow — while using nothing but the steering wheel, and made it stick. Not because of my own tiny skills but because electronic doodads all around me were able to calculate speed, weight, steer angle, lateral slide rate, coefficient of friction, and well, you name it, and then decide in a millisecond how to help me do the impossible. In that particular case, and countless others, there’s no way I could have held things together even if I could have reacted as quickly as all those microchip thingies. Principally, because I obviously couldn’t control the brakes one by one.

If I hadn’t been convinced beforehand, that particular experience would have done it. Whether we’re talking about roll stability control (RSC) or electronic stability control (ESC), which adds understeer/oversteer sensing, they’re both huge difference makers. I wouldn’t leave home without one of ’em.

I should point out that rollovers occur in only about 13% of heavy-truck fatal crash involvements, but they account for 50% of truck-occupant fatalities.

Anyway, NHTSA recently released its final report on the matter — called “Safety Benefits of Stability Control Systems For Tractor-Semitrailers.” It was conducted by the much respected University of Michigan Transportation Research Institute (UMTRI) under a co-operative agreement between NHTSA and Meritor WABCO Vehicle Control Systems. As I understand it, NHTSA supplied the money, Meritor WABCO supplied expertise to make the simulator test hardware work, among other things, and UMTRI did the testing.

This is the most comprehensive report yet on the potential for electronic stability control and roll-stability control technologies to reduce jackknifes, rollovers, and other accidents involving a loss of vehicle control. And it will very likely lead to a mandate soon because the study offered up what seems to me like a conservative estimate suggesting that RSC could prevent at least 3489 rollover crashes in the U.S. annually, rising to 4659 rollover and other loss-of-control crashes with ESC.

“They [NHTSA] are very seriously looking at mandating it on heavy trucks,” says Alan Korn, Meritor WABCO’s director of vehicle dynamics and controls. “I’m guessing they’ll make a decision in 2010, with a likely implementation in 2012 or 2013.”

Deciding to do it is one thing, but Korn allows that writing the rule will be a challenge.

A similar European Union mandate is set to take effect in 2011.

The UMTRI study was specifically designed to estimate the potential benefit of the two distinct safety systems, RSC and ESC. The former, as the study’s introduction explains, senses vehicle lateral acceleration in a curve and intervenes to slow the vehicle in accordance with an algorithm. The deceleration interventions are graduated in the following order: de-throttling; engine brake; and foundation brake application. The ESC system contains all the attributes of the RSC system and has the added capability of sensing and controlling vehicle understeer and oversteer, which are directly related to loss of control. The loss-of-control intervention strategy uses selective braking of individual wheels on the tractor.

One of the key issues in the study was that there’s very little real-world crash data to work with because stability systems haven’t been around all that long and just aren’t that widely used yet. So the study was based on the analysis of independent crash datasets using engineering and statistical techniques to estimate the probable safety benefits of stability control technologies for 5-axle tractor-semitrailer vehicles. It’s complicated stuff, to say the least, but the researchers examined two distinct accident databases and isolated crashes that fit certain criteria, namely those that suggested a given crash could have been affected by the use of RSC or ESC.

They also examined the comprehensive records of one un-named for-hire fleet that has used some variation of these technologies in significant numbers for quite a few years. There’s some interesting stuff in there, I can tell you, including the fact that icy roads mean you’re 30 times more likely to see a jackknife. I’ve never seen that risk quantified before, and 30 times is a heck of a lot.

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Rolf Lockwood is editor emeritus of Today's Trucking and a regular contributor to

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