By Robert Molloy
The NTSB has long urged that trucks and buses be equipped with electronic stability control (ESC) to help prevent and mitigate crashes. ESC automatically helps drivers maintain directional control when they cannot steer and brake quickly enough on their own. We are pleased that the National Highway Traffic Safety Administration (NHTSA) released a final rule earlier this month—FMVSS No. 136—that will help drivers of large vehicles do just that.
The new rule requires ESC systems on heavy trucks and large buses with weight ratings over 26,000 pounds, and NHTSA is beginning the process of expanding the requirement to include medium-sized vehicles between 10,000 and 26,000 pounds.
The rule covers vehicles such as the truck-tractor cargo tank semitrailer involved in the 2009 Indianapolis, Indiana, crash.
In that crash, the driver of the combination unit, which was loaded with 9,000 gallons of liquefied petroleum gas, went through a guardrail and collided with the support structure of an interstate overpass. The truck driver had been negotiating a left curve in the right lane on the connection ramp, which consisted of two southbound lanes, when the combination unit began to encroach upon the left lane, occupied by a passenger car. The truck driver responded by oversteering clockwise, causing the combination unit to veer to the right and travel onto the paved right shoulder. The driver’s excessive, rapid, evasive steering caused the cargo tank semitrailer to roll over and separate from the truck-tractor. A large explosion followed the crash, and five people were seriously injured.
The NTSB determined that the rollover might have been prevented had the truck been equipped with an ESC system. As a result of this investigation, the NTSB issued two recommendations requiring ESC on all commercial vehicles.
The new rule is a good first step. Applying the rule to all vehicles over 10,000 pounds is difficult, as hydraulic ESC systems for commercial vehicles are just beginning to be deployed. However, until ESC is expanded to cover commercial vehicles below 26,000 pounds, we may still see crashes such as the one NTSB investigated in Dolan Springs, Arizona. In that crash, a medium-size tour bus with a weight rating of 19,500 pounds was traveling on a four-lane divided highway when it started moving to the left and out of its lane at about 70 mph. The driver steered sharply back to the right, crossing both lanes and entering the right shoulder. The driver overcorrected to the left, again crossing both lanes. The bus entered a median and rolled all the way over before coming to rest on its side. As a result, seven passengers died and nine others were injured.
As vehicle safety technologies continue to be developed, ESC becomes all the more important. ESC is a necessary component of, and serves as a platform for, other life-saving technologies such as collision avoidance systems that include autonomous emergency braking (AEB). According to our Special Investigation Report (SIR) on The Use of Forward CAS to Prevent and Mitigate Rear-End Crashes, the full benefits of AEB for commercial vehicles can be achieved only when such a braking system is installed on vehicles also equipped with ESC. Equipping commercial vehicles with both AEB and ESC would be an effective countermeasure against rear-end collisions.
NHTSA estimates the new ESC rule—which will be rolled out in stages over the next four years—will prevent as many as 1,759 crashes, 649 injuries, and 49 deaths each year. When it becomes expanded to smaller vehicles, even more lives will be saved.
Robert Molloy, PhD, is the Acting Director of the NTSB’s Office of Highway Safety.
NTSB Safety Compass Blog 