Brake Assist

Brake assist is an active vehicle safety feature designed to help drivers come to a stop more quickly during an episode of emergency braking. Studies show that when making emergency stops, about half of all drivers do not press the brake fast enough or hard enough to make full use of their vehicle’s braking power (NHTSA 2010; Page et al. 2005). Brake assist is designed to recognize the tell-tale signs of emergency braking and provide drivers with extra brake support.

Brake assist is called by other names including Emergency Brake Assist (EBA) and Predictive Brake Assist (PBA). The different names are significant because though all brake assist systems have the same purpose, some are designed differently.

Brake assist is useful whenever drivers must brake hard to make an emergency stop. Brake assist usually works in combination with anti-lock braking systems (ABS) to help make braking as effective as possible while avoiding wheel lockage. There are plenty of relatively common situations that prompt heavy braking:

• A cyclist loses her balance and veers sharply in front of your vehicle.
• A large animal runs out into the road, forcing you to make an emergency stop.
• Cresting a hill, you encounter an unexpected line-up of cars and you must brake hard to avoid rear-ending another driver.

According to the National Highway Traffic Safety Administration (NHTSA) in the United States, brake assist systems fall into two general categories: electronic and mechanical. The main difference between the two is in the method used to distinguish panic braking from normal braking.

Electronic brake assist systems use an electronic control unit (ECU) that compares instances of braking to pre-set thresholds. If a driver pushes the brake down hard enough and fast enough to surpass this threshold, the ECU will determine that there is an emergency and boosts braking power. Many of these systems are adaptable, which means they will compile information about a driver’s particular braking style and tweak the thresholds to ensure the highest accuracy in emergency-situation detection. Modern drive-by-wire vehicles (i.e., vehicles with an ECU) are eligible to have electronic brake assist installed.

Older vehicles that do not have an ECU can have a mechanical brake assist system put in. Mechanical systems also use pre-set thresholds, but these are set mechanically. This means that they are not adaptable to individual drivers. These systems include a locking mechanism that activates when the valve stroke – which is directly related to how far the brake pedal is pushed – passes a critical point. Once this threshold is passed, the locking mechanism switches the source of braking power from the brake piston valve to the brake booster, which supplies the braking assistance.

The expected benefits of brake assist are many, particularly given the kinds of situations that brake assist is designed to address. The Insurance Institute for Highway Safety (IIHS) in the United States has determined that the kinds of crashes relevant to brake assist are those where the driver saw a hazard, braked, but did not stop in time. Given this, the IIHS estimates that brake assist is relevant to 417,000 crashes per year in the United States, including 3,080 fatal crashes.

Other studies also support brake assist’s effectiveness for preventing and reducing the severity of certain types of vehicle crashes. For example, NHTSA found a reduced stopped distance of up to ten feet when brake assist engaged during an emergency stop (NHTSA 2010). In addition, researchers from France estimate that brake assist would reduce injuries in 11% of all crashes, and reduce the total number of road fatalities by between 6.5% and 9% (Page et al. 2005).

Yes. As with other vehicle safety technologies, getting the most out of brake assist requires that drivers understand its purpose and limitations. Both electronic and mechanical brake assist systems activate solely on the basis of a driver’s braking commands. If the signs of panic braking are there, brake assist will engage to provide stopping support. However, inappropriate, unclear, or delayed braking actions could lead to brake assist either not activating at all or failing to provide all available support.

The first thing to remember is that brake assist has no way of seeing obstacles ahead: it cannot scan for potential hazards and does not warn drivers of any danger. As such, drivers must continue to be vigilant by paying careful attention to the road and avoid behaviour that could make identifying and reacting to obstacles more difficult, like speeding, impaired driving, fatigued driving, and distracted driving.

Also, drivers should be aware that the pre-set thresholds in both electronic and mechanical brake-assist systems by which they recognize panic braking are set deliberately high. This is to ensure that brake assist does not engage when it is not needed. However, many drivers are not used to applying the brakes hard enough and fast enough to exceed these thresholds and activate brake assist (NHTSA 2010). To get the most out of brake assist, drivers must apply the brakes forcefully and decisively as soon as they realize an emergency stop is required.

Brake assist was first introduced in high-end European vehicles in 1996. Since then, brake assist has become very popular in Europe and Australia where it is available as either standard or optional on the majority of new vehicles. In North America, brake assist was slower to reach the economy vehicle market. However, is now more commonly available as part of a safety package, and some manufacturers offer brake assist as a standard feature.