by Lawrence Herzog

Touted as breakthrough technology in the 1990s, anti-lock braking systems (ABS) are now showing discrepancies during performance testing. According to RCMP and Transport Canada research, some ABS work exceptionally well, but others, particularly in some domestic cars, trucks and SUVs, take longer to stop the vehicle – longer, in fact, than conventional brakes under identical conditions.

“We were a little surprised at the findings,” reports Cpl. Eric Brewer, an RCMP collision reconstructionist based in Kamloops, B.C., where much of the police force’s ABS testing has been conducted and analyzed. “We know that ABS aren’t always entirely effective in all conditions and on all roads. But what the research is telling us is that motorists must be aware of the limitations of their vehicles.”

Murray Klatt, a retired police officer and longtime traffic collision reconstructionist based in Regina, agrees the biggest drawback to anti-lock brakes is driver perception that vehicles with ABS can stop on a dime. “Whether you’ve got them or you don’t, stopping distances still increase with speed and, with traction issues, stopping distances become much longer,” says Klatt. “Generally speaking, anti-lock brakes work better than conventional braking systems on wet or dry pavement free of debris, but that’s not always the case on icy or rough roads. And we get a lot of both in Saskatchewan.” In order for an ABS to work effectively, tires must remain in contact with the road surface. That doesn’t always occur on rough roads or with vehicles that have poor shock absorbers.

As Klatt points out, “Once you hit the brakes, physics takes over and dictates how quickly you come to a complete stop. If you’ve been driving too fast for the conditions, you won’t be able to stop in time. It’s that simple.” For example, a car travelling 100 kilometres per hour on dry pavement requires 56 metres – about half the length of a football field – to come to a complete stop. But even just a thin layer of frost can more than double that distance (to 131 metres), while a road covered in packed snow doubles it again to 262 metres.

The Inside Scoop on ABS

  • The anti-lock braking system, originally devised in Germany in 1936, was introduced to North American automobiles in the mid-1980s and has become standard equipment on most vehicles sold in Canada.
  • An anti-lock braking system uses wheel-speed sensors to determine if one or more wheels are trying to lock up during braking, then controls them independent of each other, pumping the brakes much quicker than a human foot could. When a driver operating a four-wheel, ABS-equipped vehicle steps firmly on the brake pedal, the system automatically modulates the brake pressure at all four wheels, adjusting pressure to each wheel independently to prevent wheel lock-up.
  • If a wheel tries to lock, a series of hydraulic valves limit or reduce the braking on that wheel. This prevents skidding and allows the driver to maintain steering control. In a vehicle equipped with ABS, the driver should never pump the brake pedal.
  • In many pickup trucks, ABS work only on the rear wheels, a function called rear wheel anti lock (RWAL) that promotes directional stability only. If the driver steps too firmly on the brake pedal, the front wheels can lock and prevent steering (the same would happen with conventional brakes). But with rear wheel anti lock ABS, the vehicle continues to move in a straight line. With just enough pressure applied, a driver with RWAL can maintain steering control.
  • Most ABS, when they are activated, give drivers feedback – a mechanical sound and pulsation or increased resistance in the brake pedal as traction limits are reached. For maximum stopping power in such situations, it’s crucial that the driver continue to apply firm pressure to the pedal until the vehicle comes to a complete stop.

    For more information, see Transport Canada; ABS Education Alliance; Canadian Automobile Association; Canada Safety Council Quiz

    • Part of the time and distance needed to stop a moving vehicle is consumed by perception and reaction, which, for a rested, sober and attentive driver, is typically 1.5 seconds. At 100 km/h, that’s 42 metres of travel. For every extra second needed to detect, decide and act, a vehicle going at that speed moves 27 metres.

    Contrary to popular belief, says Klatt, anti-lock brakes don’t help the tires stop automobiles any quicker. “They just stop them more safely. Even so, as road and weather conditions deteriorate, a safe and prudent driver reduces speed. The faster you go, the less time you have to make decisions and the bigger the bang when you hit.”

    Brewer tells the story of an ABS-equipped vehicle that slid through a stop sign and across a busy highway, barely missing the high-speed cross traffic. “The driver was braking on pebbly, rolling gravel and then hit black ice on the pavement. The conditions fooled the ABS computer. You’ve got to be aware that, in those kinds of conditions, the ABS will not be able to stop the vehicle quickly.”

    When CAA Saskatchewan’s Westworld magazine examined stopping distances in spring 1999, ABS systems were beginning to make significant inroads into the market. Now most vehicles sold in North America come equipped with anti-lock braking systems, yet very few motorists have been trained to use them properly. “That lack of education means the technology is not being used to its maximum effectiveness,” Brewer says. “Many motorists learned to drive cars with regular braking systems and so developing the skills takes time and education.”

    So how can drivers safely learn the finer points of ABS braking? Transport Canada recommends motorists test their ABS-equipped vehicles in an empty parking lot with lots of room to manoeuvre. Practise hard braking stops from 30 km/h and pay attention to brake-pedal feel, the sound the system makes and the effect on vehicle control during braking in both a straight line and turns. Remember that ABS will perform differently depending on the road surface and/or weather conditions.

    Still, what positively sets anti-lock brakes apart from their conventional predecessors is greater vehicle stability in an emergency and the ability to make a significant difference in avoiding obstacles while braking – because ABS allow drivers to steer while applying maximum braking. “However, motorists must remember that steering while braking increases stopping distances by between 25 and 50 per cent,” Brewer notes. The braking and steering ability of the vehicle is limited by the amount of traction the tires can generate. If a driver has to steer while braking, then the traction is divided between both tasks.

    Testing also shows that good snow tires reduce the stopping distance of ABS-equipped vehicles in winter conditions (Transport Canada urges the installation of four snow tires to maintain equal traction on each wheel). Nevertheless, it’s recommended that drivers allow for a longer stopping distance with ABS than for conventional brakes when driving on gravel, sand, ice, snow and mud. This is because the rotating tire will stay on top of these low-traction road surfaces and effectively “float” on the boundary layer. (Conversely, a non-ABS-braked vehicle can lock its tires and create a snowplow effect in front of the tires that helps slow the vehicle. These locked tires can often find more traction below this “boundary layer.”)

    Other road hazards ABS drivers should watch for are railway tracks, potholes, manhole covers – even road markings when it is raining. When loss of control is imminent, though, “intelligent” stability and handling systems now available on some higher-end vehicles provide ABS drivers with greater manipulation. These so-called anti-yaw systems use sensors that detect the direction the vehicle is travelling and compare it to the direction the driver is steering. When the system detects a discrepancy, it intervenes by controlling the amount of braking force applied to the tires to bring the movement of the vehicle back in line with the driver’s intentions.

    But all the technological advancement in the world won’t keep a bad driver safe. “It all comes down to the human being behind the wheel,” Klatt concludes. “You can’t rely on the technology to get you out of trouble; you’ve got to drive the conditions. And the only way to reduce stopping distance is to slow down. It’s simple physics.”

    This feature originally appeared in Westworld Saskatchewan, CAA Saskatchewan’s magazine to its members.

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