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ABS, EBD, and BA ABS revolutionized brake safety. Following the adoption of seatbelts through the middle of the 20th century and the introduction of the airbag in the 1970s, the biggest change in the field of car safety came in the form of antilock brake systems (ABS) in the 1980s. Antilock brake systems allow drivers to jam on the brakes and still maintain control, thanks to a clever design that prevents brakes from locking up. ABS works by gathering wheel-rotation information from sensors and rapidly pulsing the brakes with an electrohydraulic control unit to distribute brake fluid stored under high pressure. Many contemporary vehicles have four-channel ABS systems, where each wheel is monitored for rotation and the information forwarded to a processor. A few vehicles, mostly light trucks, monitor just the front wheels and the drive shaft in what's called two-channel ABS, but this design is less common. ABS was the most dramatic advance in brake technology since discs brakes replaced drum brakes on new vehicles. But it was just the beginning of combining electronics with hydraulic brake systems to improve safety. With the widespread adoption of ABS systems, the next advancement was to more precisely control the brake pressure for each wheel. For decades, this was accomplished mechanically, with valves that would proportion more fluid pressure to the front wheels where more braking power was needed because of weight shift during braking. But the mechanical system had to deal with an assumed need and couldn't factor changes in passenger or cargo loading. To solve the problem, Electronic Brakeforce Distribution (EBD) was developed to work with ABS to precisely control hydraulic pressure at each wheel. The system achieves this task by monitoring wheel movement and ride height. When a vehicle is loaded, the system can direct additional pressure to the rear wheels to deal with added loads, but not so much as to cause lockup. A four-channel ABS system can do much of this task, but it intervenes after the fact. With EBD, the system kicks in earlier, leading to shorter stopping distances and the prevention of more accidents. With ABS and EBD gaining in popularity, engineers looked for a system that could increase responsiveness of braking systems even further by priming the brakes immediately prior to emergency braking. The resulting technology was Brake Assist (BA), a system that uses throttle-by-wire, a common attribute in new vehicles, to detect when the driver has suddenly lifted his or her foot from the gas pedal. When that quick lift occurs, the brake system is instantly primed for a quick application. With BA engaged, the brake pedal needs little travel and stopping is hastened dramatically. Like EBD, the brake-assist function relies on ABS technology to operate; in this case, it's the accumulated hydraulic brake pressure. With all the ABS, EBD, and BA acronyms on board, there's far less excuse for rear-ending that hapless soul in front of your vehicle.