Driving with ABS: STOMP, STAY and STEER!
In my last column, I discussed how vehicles “burn off” energy and come to a stop. I also mentioned that when a vehicle locks its wheels, the tires slide across the road surface and create tremendous amounts of heat. This process causes the vehicle to lose all steering control and skid in a relatively straight line until it comes to a stop or strikes another object. I’m sure many of you asked, “What about rigs equipped with an anti-lock brake system (ABS)?”
Years ago, vehicle designers recognized that when a vehicle enters a skid, all steering control is lost. In an effort to solve this problem, ABS was born. ABS allows a vehicle to maintain steering control, even when the brakes are applied forcefully.
With the advent of ABS, firefighters now have another apparatus-related issue on which to train to keep us (and everyone around us) safe. The first step in an ABS training program should be for fire departments to readily identify which vehicles are equipped with ABS and which are not. In departments with mixed apparatus fleets, the type of braking system should be clearly marked in plain view of the driver. The reason: The methods used to stop an ABS-equipped vehicle are vastly different from the methods used to stop a non-ABS-equipped vehicle.
In the days before ABS, EVOC classes taught us how to “pump the brakes” during panic stops. Drivers were taught to forcefully apply the brakes until they felt the wheels about to lock. Drivers were told to then ease off the brake pedal and manually pump the brakes with their foot, hopefully providing maximum stopping power, while not locking the wheels and causing the vehicle to skid. While this idea sounds good in theory, it isn’t that easy in practice. For this reason, the job of pumping the brakes was given to a microprocessor. In an ABS-equipped vehicle, sensors on the wheels detect when the wheel is about to lock. Once these sensors detect impending lock-up, the microprocessor then “pumps” the brakes for us, preventing the tires from skidding.
When ABS first gained popularity in everyday automobiles [Better word that “everyday” automobiles? regular? civilian?], I would often be called to investigate accidents that involved elderly drivers. These drivers had been driving for 40 or 50 years with traditional, non-ABS-equipped vehicles. I would often ask these drivers what caused the crash, and I always got the same answer: “Officer, the other vehicle pulled out in front of me and I slammed on my brakes. Then the brakes stopped working.”
Upon further investigation, I would ask what made this person think their brakes stopped working. The answer was always the same: “As I put my foot down on the pedal, the brake pedal started thumping.” In reality, the brakes were working fine. The problem was that the ABS was engaging; these drivers had simply never experienced this type of situation. Instead of leaving their foot down and steering around the hazard, they took their foot off the brake and ended up in an accident. It is for this reason that we must train fire apparatus operators on what it feels like when the ABS kicks in.
A recommended training practice is to take a vehicle out to an empty parking lot and speed up to about 15 to 20 mph. Instruct the driver to slam on the brakes, leaving their foot down for the entire stopping distance. As the ABS engages, the driver will feel the pedal start to thump underneath their foot. While some may argue that this type of training may cause undue wear and tear on the vehicle, I ask you this: Where would you like your driver to first encounter what it feels like for the ABS to engage? In an empty parking lot at 15 mph under relatively controlled conditions, or on a rain-slicked roadway at 60 mph as the driver attempts to evade a hazard in the roadway? It’s much cheaper to send the vehicle out to have the tires and brakes checked after ABS training than to have a driver experience the ABS engaging for the first time in an emergency situation and not know what to do.
During ABS training, drivers should learn the concepts of STOMP, STAY and STEER. In other words, when faced with an emergency stopping situation, the driver should STOMP down on the brake pedal, STAY on the brake pedal (not PUMP the brake pedal) and then STEER around whatever hazard may be in the roadway. During this emergency stopping process, the driver must realize that the brake pedal may begin to thump against their foot. Make sure they understand that this is OK; it means the ABS is working. Keep your foot down and do what you need to do to try and avoid the accident. Bear in mind, however, that in an unstable, top-heavy fire truck, sudden steering maneuvers may cause the vehicle to rollover. Don’t put yourself in an out-of-the-frying-pan-into-the-fire situation.
For more information on brakes and anti-lock brake systems, please visit http://www.drivetosurvive.org/brakes.htm. There is also a good training video produced by the U.S. Department of Transportation that discusses ABS on heavy vehicles. This video can be found at http://www.fmcsa.dot.gov/multimedia/abstruck-wmv-broadband-stre.wmv. As always, training is the key to safety.