Drive To Survive: Anti-Lock Brake Systems (ABS)

By Chris Daly

Editor’s Note: "Drive to Survive" is 10-part series that will be published in SIZE UP magazine and The NYSAFC Bugle. Click to read the previous stories in this series: "Drive to Survive: An Introduction" and "Drive to Survive: Energy."

In the last article of this series, we discussed how a vehicle "burns off" kinetic energy and comes to a stop. I mentioned that when the tires on a vehicle lock up, the tires will 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 ABS brakes?" In this article, we will discuss the issues associated with ABS brakes.

Years ago, vehicle designers recognized that when a vehicle enters a skid, all steering control is lost. In an effort to solve this problem, anti-lock brake systems (ABS) were born. Anti-lock brakes allow a vehicle to maintain steering control, even when the brakes are applied forcefully. 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 fleets of apparatus, the type of braking system should be clearly marked in plain view of the driver. The reason for this is that the methods used to stop an ABS equipped vehicle are vastly different from the methods used to stop a non-ABS 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 then told to ease off the brake pedal and manually pump the brakes with their foot in an attempt to provide 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 computer. In an ABS equipped vehicle, sensors on the wheels detect when a wheel is about to lock. Once these sensors detect impending lock-up, the computer then "pumps" the brakes for us, preventing the tires from skidding.

When ABS first gained popularity in everyday automobiles, 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 had caused the crash to occur and I always seemed to get 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 that 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 and these drivers had no experience with 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 crashing into the other vehicle. It is for this reason that we must train fire apparatus operators 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 15-20 mph. Instruct the driver to slam on the brakes, leaving his or her foot down for the entire stopping distance. As the ABS engages, the driver will feel the pedal start to "thump" underneath his/her 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 be taught the idea of STOMP, STAY, and STEER. This means that 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 his/her foot. 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. However, keep in mind that in an unstable, top-heavy fire truck, sudden steering maneuvers can send the vehicle into a rollover situation. Don’t put yourself in an "out of the frying pan, into the fire" situation. Rolling the truck to avoid a squirrel is probably not a good idea.

About the Author:
Chris Daly is a 23-year veteran of the fire service and a full time police officer who specializes in the reconstruction of serious vehicle crashes and emergency vehicle crashes. He developed the "Drive to Survive" training program and lectures nationally on the prevention of emergency vehicle crashes. Daly has been a contributing author to Fire Engineering magazine and Firerescue1.com. He has a master’s degree in safety from Johns Hopkins University. Click here to email Chris Daly for more information.