Just more than one year ago, the National Highway Traffic Safety Administration (NHTSA) published a Final Rule requiring that all heavy trucks made Aug. 1, 2017, and after be equipped with electronic stability control (ESC) systems on “typical three-axle tractors.”
For its stability mandate, NHTSA chose ESC over Roll Stability Control, which Fred Andersky, Bendix director of government and industry affairs, says offers an all-in-one higher level of protection for the driver.
“[ESC] technology is designed to help mitigate both roll-over and loss of control situations on slick surfaces,” he says.
Both ESC and roll-only systems work in conjunction with the truck’s antilock braking system (ABS) system, but full-stability systems use more sensors.
“The steer angle sensor measures the driver input … so this is the sensor that actually goes right through the center of the steering column,” he says. “We also add a directional stability sensor, and this tells us which direction the vehicle is going. When the driver goes left and the vehicle goes in any other directions but left … that’s when electronic stability control kicks in.”
MeritorWABCO says the truck’s engine control unit constantly compares the vehicle’s actual movement to performance models using various vehicle sensors. If the vehicle shows a tendency to leave the driver’s intended path (oversteer or understeer) or exceed a critical lateral acceleration threshold, the system intervenes by selectively applying appropriate brakes and/or reducing the throttle to better align the vehicle to the driver’s path of travel or speed.
“The best way to mitigate a roll over is to slow the vehicle down as quickly as possible,” Andersky says, “so [ESC] cuts the throttle and applies the brakes on the steer, drive and trailer axles.”
Roll over only systems cut throttle while applying the brakes on drive and trailer axles.
“In a loss of control situation, roll stability doesn’t do anything because it doesn’t know there’s a loss of control because it doesn’t have those two sensors to let it know that, ‘hey, we’ve got a loss of control.’”
The level of sophisticated decision-making the ESC can process in nanoseconds, Andersy says, was the driving factor in NHTSA opting for an ESC mandate versus roll-only.
“In a case of a jackknife going to the left, we may not want to apply all of the brakes,” he says. “We may just want to apply the left steer axle and the trailer brakes to help straighten out the combination and we can do that because [ESC] can control where the brakes are applied on the tractor [and trailer] and how much braking force is applied.”
Fleets are already taking note of the benefits of ESC protection. Andersky notes Bendix typically sees its Electronic Stability Program (ESP) systems out-sell roll-only platforms by as much as 3:1, depending on OEs and truck specs.
“The reality is [ESC] is a better roll over system because it can read the roll over situation sooner because roll overs actually start at the front of the vehicle with steering and speed input,” he says. “Since we’re reading that, we can react earlier to a roll over situation.”
Bendix Commercial Vehicle Systems LLC says it has delivered more than 450,000 of its ESP system its since its introduction in 2005. In 2015, Andersky says about 35 percent of new tractors were equipped with some form of stability control.
“My expectation is that we would probably see that rise with the mandate to probably about 80 to 90 percent [industry-wide],” he adds.
NHTSA estimates monetary savings on crashes, reduced congestion and damage to property will yield a yearly societal benefit that ranges from $3.6 million and $19.2 million.