RSC Vs. ESC
Korn says more and more fleets are adopting stability control systems, including electronic stability control (ESC) and roll stability control (RSC) systems. ESC provides full stability control, working to prevent both rollovers and loss of control incidents. RSC is built to primarily address rollovers, but not loss of control.
Using the anti-lock brake system, the technology that powers RSC uses a lateral accelerometer, a sensor that measures the lateral acceleration, the main cause of a rollover, Korn says. Valves are automatically applied to dethrottle the engine, while the drive and trailer axle brakes are also automatically engaged.
ESC has the same technology to control rollovers as RSC, but it uses two additional sensors, Korn explains. The first, a steering wheel sensor, tells the system where the driver is pointing the vehicle. The second, a gyro sensor, measures how much the vehicle is actually turning. When there's a disconnect between the two, the system automatically intervenes. The individual foundation brakes kick in as a counteractive force.
Stability Control Study
Korn says a mandate for these systems could be in the cards, especially following the results of a recent study conducted by The University of Michigan Transportation Research Institute under a cooperative agreement between the National Highway Traffic Safety Administration and Meritor Wabco Vehicle Control Systems. That study found that because ESC systems are more comprehensive, they offer more safety benefits than RSC.
With ESC installed on the vehicle, the number of annual heavy truck crashes would decrease by 4,659 crashes, preventing 126 fatalities and 5,909 injuries, according to the study. If all trucks were outfitted with ESC, it would result in savings of $1.74 billion annually because of the rollovers prevented. With RSC installed on the vehicle, there would be 3,489 less crashes, preventing 106 fatalities and 4,384 injuries. Having all trucks outfitted with RSC would save $1.46 billion annually, according to the data.
According to Korn, the study's researchers set out to measure the effectiveness of stability control systems. Using information from several databases including the GES database, the Trucks Involved in Fatal Accidents database and the Large Truck Crash Causation Study, UMTRI determined how many of the accidents involved rollovers versus loss of control. They were categorized according to what conditions they occurred in, including type of road (curvy or straight) and condition of road (wet or dry). Using data collected from TIFA and GES on a five-year annual average, the researchers found that there were 6,874 crashes involving rollovers per year and 4,350 crashes involving loss of control.
Using a hardware-in-the-loop simulation, or HiL, the researchers put the vehicles through a computer software maneuver simulation, in order to accurately measure how the stability control system was reacting. They used HiL for the rollover incidents, and tested the systems for loss of control in the field. With these methods, they were able to put a value of effectiveness on the different stability control systems in mitigating rollovers and loss of control, according to different conditions.
In the end, they found that ESC and RSC were most effective on curvy, dry roads, with prevention rates of 75 percent and 71 percent, respectively.
Apex Logistics, which uses Meritor Wabco's Roll Stability Control system, has seen the benefits. "We averaged three rollovers a year until Jan. 1, 2005, when we started equipping our tractors with RSC," said Mike Siebert, director of maintenance. "We haven't had a rollover since."