The use of electronic stability control (ESC) to prevent rollovers is nothing new — the technology has been saving lives in passenger cars and light trucks for years. It hasn’t been required on commercial vehicles until now.
On June 3, 2015, U.S. Transportation Secretary Anthony Foxx announced the establishment of a new standard, Federal Motor Vehicle Safety Standard No. 136, Electronic Stability Systems for Heavy Vehicles. The standard requires truck tractors and certain buses with a gross vehicle weight rating (GVWR) of greater than 26,000 pounds to be equipped with ESC beginning 2017.
According to the NHTSA, the requirement will save nearly 50 lives and prevent up to 1,759 crashes each year, and provide net economic benefits of more than $300 million annually.
There are two types of stability control systems: RSC and ESC
Roll Stability Control (RSC) systems are designed to prevent rollover by decelerating the vehicle using braking and engine torque control. RSC was not proposed because the agency said the net benefits were lower than the net benefits from an ESC mandate.
Electronic Stability Control (ESC) systems include all of the functions of an RSC plus the ability to mitigate severe oversteer or understeer by automatically applying brake force at selected wheel-ends to help maintain directional control of a vehicle.
Stability Control impact analysis for heavy vehicles:
What happens in a tractor-trailer rollover?
As you move to vehicles with a higher center of gravity, the g-factor (amount of force necessary to roll them) becomes smaller. The lower the g-factor, the less stable the vehicle. For example: a car will rollover at 1.3 Gs, whereas a fully loaded semi and trailer will roll over at 0.4 Gs. In most cases, cars will slide out of a curve before they roll over. Trucks with high centers of gravity, however, tend to roll over rather than slide.
Because the trailer has a higher center of gravity than the tractor, the trailer begins to roll over first. The inside rear trailer tire will lift off first. A cushioning effect from the suspension system and the trailer itself will absorb some shock. The fifth wheel and the tractor suspension will also absorb some twisting. Eventually, the tractor’s inside drive tires will lift off.
The driver inside the cab is insulated from the first effects of a rollover due to the suspension system and cushioning effect. In fact, the driver seldom feels anything happening, but may see the trailer starting to roll in side mirrors. Only then, the driver may feel the tractor starting to roll.
In a straight truck configuration, the driver is more apt to feel the incipient rollover, which requires immediate control input from the driver. Most often, the immediate control is hitting the brakes, which is counter productive and can actually increase the chance of rollover.
Can trucks be retrofitted with ESC?
The new standard excludes the retrofitting of currently in-service trucks with an ESC system. The cost of installing ESC systems to your existing fleet varies by manufacturer and system features/performance. But one thing is certain, effective stability technology can help prevent costly tractor-trailer rollovers.
Nationwide does not endorse any one stability technology or manufacturer, but we do encourage you to watch Bendix’s ESP Electronic Stability Program Video to see commercial vehicles being tested both with and without stability technology.
Risk Management recommends following best practices
No stability control system will ever prevent all rollovers. At the end of the day, trucks are driven by people — and people make mistakes.
Even with electronic stability control, drivers must continue to follow rollover prevention best practices and other safe driving best practices to maintain control of their vehicles and help keep our roadways safe.
Nationwide hopes you will join us in promoting tractor-trailer rollover prevention.