Yes, Anti-Rollover Systems Work

This reporter can testify that the antirollover systems work, at least in demonstration and testing situations. I've driven trucks and tractor-trailers equipped with the products on big parking lots and saw how they automatically slowed the rigs in tight turns, preventing what would otherwise have been certain rollovers. The difference between going into a turn with a system turned on or off is dramatic, but of course production versions of the systems are always on alert.

The most recent demo experience was a year ago in Washington, D.C., where ArvinMeritor and Wabco people showed off two products for trucks and tractors that they jointly make and market: Roll Stability Control (RSC), which concentrates on center of gravity and lateral and braking forces, and Electronic Stability Control (ESC), a more advanced truck and tractor system that has additional sensors to measure steering input and yaw, or rotation, motion.

There's also Roll Stability Support (RSS) for trailers. This keys on lateral movements and g-forces in the braking system and airbag suspension. RSS acts alone to keep a trailer from doing its roll-and-pull act in dangerous maneuvers by applying its brakes. In such events, the trailer begins rolling first and soon pulls over the tractor. The driver doesn't notice what's happening because there's no seat-of-the-pants feel as the trailer begins tipping, and he doesn't see it because he's looking into the turning roadway, not at his mirrors.

If he did glance into the mirrors, as I did while driving a Freightliner Century-andflatbed rig during the demos, he'd see the trailer contorting as its rear end rolls first and the twisting forces travel forward toward the tractor. But in the demo, an outrigger on each side of the trailer stopped any rollover; the tire on the one on the outside of a turn touches down and that's as far as the trailer will go.

That happens when a test system is switched off. When it's on, a roll is arrested because the electronic system orders th engine to reduce power, then applies the brakes via the tractor's ABS controller. The rig's speed is reduced by 10 mph or more as it goes through a turn and finishes the maneuver on all of its regular 18 wheels.

A near-rollover in a straight truck is more violent. I experienced this at the Meritor Wabco demo, which used a Stewart & Stevenson military 4x4 cargo truck, and at a Bendix demo earlier in the year, at the Las Vegas Speedway. Bendix had its stability system, which also has sensors to measure to steering input and accelerometers to gauge yaw and lateral g-forces, installed on a Mack Granite 6x4 mixer. Going into sharp turns, rolls began at the truck's rear as the tandem's wheels on the inside of the turn suddenly began lifting. Within milliseconds the front of the truck rose, too, and anybody in the cab was shaken roughly in the process.

With the system switched on, the truck's speed slowed as its engine power was first cut, then its brakes activated, and rollovers were averted. The system also cut power on me several times as I made sharp right turns at the other end of the parking lot; I was driving too slow for it to apply the brakes, but it knew that the truck was still moving too fast into the turns for its own good. In the sharp turn and lane-change maneuvers, the system simultaneously cut power and applied the brakes.

On a tractor, the Bendix stability system sends signals that are read by the trailer's ABS, whether it's Bendix's or another manufacturer's. If the trailer is an older one without ABS, the system on the tractor sends pulsing pneumatic signals back to the trailer brakes, effectively turning them into ABScontrolled units. Bendix also has a trailer system called TEPS-4, and has two others coming out later this year.

Meritor Wabco and Bendix demonstrate their rigs with stability control at various venues throughout the year. If you hear of one, try to go to it and experience what the systems can do. As the demonstrators will tell you, the systems won't stop all rollovers, but even so, you'll begin believing in them.