Using data to fight rollovers

With all the debate over the causes of automobile/large truck crashes, it’s easy to overlook a significant safety problem – at least when measured in terms of the well-being of your employees. According to Department of Transportation statistics, in 2001, approximately 476 truck drivers were killed and 12,000 injured in crashes involving just a truck or tractor-trailer combination and no other vehicles. Of those totals, more than 31 percent of the fatalities and about 50 percent of the injuries occurred during rollovers.

It shouldn’t be a surprise that rollovers represent such a big share of the single-vehicle deaths and injuries. Consider what happens in a rollover. There’s a good chance that the driver’s head will strike the ceiling or window of the cab – even when he is wearing a seatbelt.

Freightliner Corp. has searched for a solution to the rollovers caused by drivers who power through corners too fast, not understanding a truck’s rollover limit. Initially unveiled conceptually about four years ago, the system, called Roll Advisor and Control, is now past the prototype stage of development and is in field-testing. Freightliner demonstrated the device in June at the National Intelligent Vehicle Initiative meeting, held in McLean, Va.

Scott Smith, Freightliner’s executive engineer for customer and technology programs says the company, in its search for technology to deal with the rollover problem, worked with Meritor/Wabco to design and develop the system. Now Freightliner is working with Praxair and the University of Michigan Transportation Research Institute to test Roll Advisor and Control. Praxair hauls tank loads of materials like liquid nitrogen that can shift or slosh, posing great danger in case of an accident. The carrier’s interest in Roll Advisor and Control, therefore, should come as no surprise.

The anti-rollover system is an astonishing demonstration of high-tech capability. It monitors such factors as wheel slip from the ABS system and vehicle speed and engine torque output from engine ECU inputs. It calculates the vehicle’s center of gravity based on the information it receives. Much of the magic lies in comparing the rates of wheel slip from side-to-side in corners, as slip varies depending on how much the rig leans. The end result is the ability to accurately calculate the risk of a rollover under any road and load condition. Rollovers normally occur at about 1/3 G, but the actual lateral acceleration rate and speed when rollovers happen varies depending upon several factors, including the weight of the load and its height and that of the trailer structure.

All this knowledge, deciphered from sensor data via computer algorithms, lets the system know when a vehicle is approaching rollover. Smith reports that the system has three levels of warning messages, giving distinctive buzzing sounds to the driver, depending upon how close the truck is to losing its balance. One of its purposes is to record near-rollover events and then post information on the dash for the driver in the hope of training him to avoid such situations in the future. “Field testing has shown it can be done. When this communication was turned off, there was a statistically measurable difference in driver behavior,” Smith says.

When rollover is actually imminent, the Roll Advisor goes into roll control mode. The system first defuels the engine. If that doesn’t drop the G-force enough, it then applies the engine brake. If necessary, it will even apply the service brakes through the ABS hardware. The system can actually slow the vehicle while controlling wheelslip to prevent lockup, even though much of the hardware consists of standard ABS components. ABS in reverse!

Freightliner engineers had tricked up a bobtail tractor, fooling its computer into thinking rollover would occur at a low speed, in order to demonstrate the system’s performance. I took a ride and observed both the system’s warnings and actions. They consistently reflected conditions and took effective action.

Smith could not say exactly when the system will hit the market or estimate the cost yet, but, for those fleets hauling shifting loads especially, this could be a real lifesaver.