Nearly 200,000 crashes involving tractor-trailers occurred in the US this past year--an average of one crash every three minutes—and I got to watch one a month ago driving back to Santa Barbara, CA, from an event in Las Vegas. It occurred on the transition ramp from the Westbound Highway 14 to the Northbound Interstate 5, a fairly sharp-climbing, right-hand bend leading out of an equally steep downhill plunge.
I began watching a truck-trailer rig toting a large backhoe-loader about a half-mile before the ramp, thinking he would probably knock off 20-or-so mph before settling into the turn, an action allowing me to pass him before the ramp necked down to a single lane. But as we neared the corner it became apparent that the driver had misjudged the situation, so what happened next was preordained—a classic example of last-ditch overreaction. First, the driver dove hard onto the brakes as he entered the turn causing the trailer to load up against the truck producing an initial understeer condition. Then the driver responded by increasing the steering input inducing oversteer, which led to what under the circumstances was an immediate loss of control, jackknife, and an uncontrolled slide into the guard rail.
As I reflect on the accident with 20/20 hindsight, I can’t say with certainty that situation was salvageable, but it wasn’t the extra 20 mph that put the rig into the wall—rather, the driver’s flawed reactions. It’s tempting to say, “Yeah, driver error,” and let it go at that. But is that all there is to it? Maybe not. Perhaps an electronic stability control (ESC) system could have changed the outcome.
ESC uses sensors to detect when a driver is about to lose control and automatically intervenes to provide stability and help the driver maintain the intended course, especially in oversteering and understeering situations.
A number of studies have been conducted testing the effectiveness of ESC, verifying that ESC does, in fact, work. Five different studies projected a 30%–35% reduction in single-vehicle crashes, thanks to ESC.
ESC incorporates antilock brake and traction control systems that prevent wheel lock when braking and wheel spin when accelerating, incorporating the actions of both systems, acting to counter lateral forces to further reduce the risk of skidding in all driving situations. Simply put, ESC constantly compares the driver’s intention with the vehicle’s actual behavior.
Because deployment of the stability technologies for large trucks has only occurred recently, national crash databases do not yet have a sufficient amount of data on the performance of these technologies. Employing a novel approach to examine the potential benefits of these systems, researchers used national crash databases to select crash scenarios that could likely benefit from the technologies and estimated the probable effectiveness of each. The analysis was based on probable outcome estimates derived from hardware-in-the loop simulation (HiL), field-test experience, expert panel assessment, and fleet crash data.
Findings of the study indicate that stability-control systems provide substantial safety benefits for tractor-semitrailers. If all five-axle tractor-semitrailer vehicles operating on US roads were fitted with ESC, the technology could prevent 4,659 rollover crashes and save an estimated 126 lives. That’s something to consider for your fleet.