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Status Report, Vol. 50, No. 6 | July 30, 2015 Subscribe

Truck tractors, large buses will get ESC under new rule

Daimler Trucks North America

Large trucks and buses soon will be equipped with the same technology that has slashed rollover crashes in passenger vehicles, thanks to a new federal requirement for electronic stability control (ESC) on heavy vehicles.

The rule, which was finalized in June, takes effect for almost all new truck tractors in 2017 and in 2018 for new buses larger than 33,000 pounds. The remaining types of truck tractors, as well as buses between 26,000 and 33,000 pounds, have until 2019.

The National Highway Traffic Safety Administration (NHTSA) estimates the requirement will prevent up to 1,759 crashes, 649 injuries and 49 deaths each year. An earlier analysis by the Institute found that ESC on tractor-trailers could potentially prevent 295 fatal crashes a year, assuming the technology was 100 percent effective. Looking at all large trucks, not just tractor-trailers, ESC would be relevant to 439 fatal crashes (see "Large trucks to benefit from technology designed to help prevent crashes," May 20, 2010).

"ESC has been saving lives of passenger vehicle occupants for years," says Anne McCartt, IIHS senior vice president for research. "Now this regulation will allow more road users to benefit from it."

Institute studies have found that ESC on cars and SUVs reduces fatal single-vehicle crash risk by 49 percent and fatal multiple-vehicle crash risk by 20 percent (see "Stability control reduces fatal crash risk by a third," June 19, 2010).

ESC is one of two types of stability control available for heavy vehicles. The other is roll stability control. NHTSA chose to mandate ESC, which is more expensive but also more effective than roll stability control. Both systems can intervene if lateral acceleration and wheel speed indicate a high rollover risk, but only ESC measures the tractor's directional stability. As a result, it can intervene in a broader array of crashes, including some that involve loss of control but not rolling over (see "Truck tractors, buses could get standard ESC under NHTSA proposal," Aug. 14, 2012).

NHTSA estimates that ESC on large trucks and buses can reduce "untripped" rollovers — those that aren't precipitated by striking something or driving onto soft soil — by 40 to 56 percent. Loss-of-control crashes caused by severe oversteer or understeer can be cut by 14 percent, the agency says.

Without the new regulation, NHTSA estimates that 34 percent of truck tractors and 80 percent of large buses would have had ESC by 2018, while an additional 21 percent of truck tractors would have had roll stability control. Its estimate of the rule's impact is based on the difference between those numbers and having 100 percent of the vehicles equipped with ESC.

Compliance with the requirement will be tested using a "J-turn" test that replicates a curved highway off-ramp.

The rule doesn't cover single-unit trucks, which were involved in 35 percent of all fatal truck crashes in 2013. NHTSA is studying the feasibility and potential benefits of requiring ESC for them.

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