ABS, or anti-lock braking systems, is an automatic system that prevents brakes from locking up, which would cause the vehicle to skid uncontrollably. In systems that do not have ABS, drivers have to manually pump their brakes to avoid lock up.
ABS does it for the driver so that they can focus on steering. Primitive ABS dates back to the early 1900s, but the modern systems we use today has been progressing since the 1970s. The way ABS works is by sensing the speed of rotation of each of the tires relative to vehicle itself. When one or more tires slow down and the risk of locked brakes goes up, ABS uses hydraulic pressure to rapidly adjust so the vehicle can safely slow down.
Modern ABS can also make several other adjustments automatically to increase our control of the vehicles, such as being able to sense the direction the steering wheel is turned and whether or not the vehicle is travelling in that direction.
When ABS or another system fails on a semi truck, commercial roadside assistance can get the driver back on the road quickly.