Emergency (or parking) brakes work as a secondary system to the standard brakes used on a daily basis. They are controlled by a physical system and regulated by an equalizer.
What an Equalizer Does
Parking brakes are engaged by pulling a lever somewhere near the driver's seat. That lever tightens a cable that leads to two or four (depending on the vehicle) tires which then engages the brakes. According to AA1car.com a parking brake equalizer is used to distribute the breaking pressure evenly across all tires.
How an Equalizer works
The equalizer works by connecting the single cable leading from the cab of the car to the undercarriage to two separate cables leading to the individual tires. This evenly distributes the force applied by the parking brake lever.
Why Equalizers are Necessary.
If uneven braking occurs, especially at high speeds, the steering of the vehicle may be compromised. If you've ever had the brakes on one tire grab while you were driving you will understand why this is bad. By spreading the force evenly the car can be stopped without affecting steering.
