What are the three brakes?

In road-vehicle contexts, the three brakes generally refer to the service (foot) brake, the parking (hand or electronic) brake, and the emergency brake. The exact meaning depends on the vehicle: in heavy trucks and buses with air brakes, these are three distinct systems; in passenger cars, “emergency brake” commonly refers to the parking brake, with additional fail-safes and auxiliary braking provided by the drivetrain or electronics. Below, we explain how the term is used across vehicle types and why it matters for safety and maintenance.

The three brakes in heavy trucks and buses (air-brake systems)

Commercial vehicles that use compressed air for braking are engineered with redundancy. Training manuals and regulations describe three braking systems, each serving a specific purpose in normal driving, parking, and failure scenarios.

• Service brake system (foot brake): The primary, pedal-operated brakes used to slow or stop the vehicle during normal driving. In air-brake vehicles, this modulates compressed air to apply foundation brakes at each wheel.
• Parking brake system (spring brakes): A mechanically applied system (typically heavy springs that clamp the brakes) engaged by a parking control valve when the vehicle is parked. Air pressure holds these springs released while driving; removing air sets the brakes.
• Emergency brake system: A backup that automatically or manually applies the spring brakes if air pressure drops too low or there’s a failure in the service system, helping the driver stop the vehicle safely.

Together, these systems provide graduated control for routine braking, secure hold when stationary, and fail-safe stopping power in the event of a system fault.

How this maps to passenger cars and light trucks

In cars, you’ll typically interact with two distinct controls: the service (foot) brake and the parking brake, which is often colloquially called the emergency brake. Modern vehicles layer electronic and mechanical safeguards to provide a “third line” of braking in emergencies.

Below are the main braking elements you’ll encounter in today’s cars and how they align with the “three brakes” concept.

• Service (foot) brake: Hydraulically actuated disc/drum brakes operated by the brake pedal; almost all modern cars have anti-lock braking (ABS) for stability.
• Parking brake (a.k.a. hand brake or electronic park brake, EPB): A mechanical or motor-driven system that locks the rear wheels to hold the car when parked and can provide limited emergency stopping if the foot brake fails.
• Emergency/auxiliary braking: Not a separate lever in most cars, but provided through redundancy (dual-circuit hydraulics), engine braking from the powertrain, and electronic systems like brake assist and stability control that maximize stopping effectiveness.

Practically, drivers will see two controls (pedal and parking brake), while the “third brake” function is delivered via built-in redundancy and electronic aids designed to help in failure or panic situations.

Trains and transit vehicles

Rail systems also rely on a three-layer approach, though the technology differs from road vehicles. Operators typically use a combination of pneumatic and electrical braking modes to manage speed, energy efficiency, and emergency stops.

• Service (pneumatic) brake: The standard train brake using air pressure modulation to apply brake shoes or pads along the consist.
• Dynamic/regenerative brake: Traction motors operate as generators to slow the train, dissipating or feeding energy back to the power system, reducing wear on mechanical brakes.
• Emergency brake: A rapid, full-application braking mode triggered by the operator or passengers (in some systems) to stop the train as quickly as safely possible.

This layered design improves control during normal operations, enhances energy efficiency, and provides robust stopping capability when needed most.

Motorcycles and bicycles

Two-wheelers don’t use the “three brakes” label, but similar principles apply: primary controls for normal riding, a means to hold the vehicle stationary, and techniques or systems to assist during emergencies.

• Motorcycles: Front and rear service brakes (often ABS-equipped) plus engine braking via downshifts; some touring or performance bikes add cornering ABS and linked braking systems.
• Bicycles: Typically front and rear rim or disc brakes; coaster/drum hubs can provide a parking hold and basic braking without hand levers.

While the terminology differs, riders still rely on primary braking, a stationary hold, and auxiliary techniques to maintain safety.

Safety, maintenance, and usage tips

Regardless of vehicle, understanding each braking layer and keeping systems in good condition is essential for safe operation.

• Test your parking brake periodically to ensure it holds the vehicle on a slope.
• In air-brake vehicles, drain air tanks as required, monitor air pressure gauges, and perform pre-trip checks on service, parking, and emergency functions.
• Use engine braking on long descents (appropriate gear or retarder) to prevent overheating service brakes.
• Ensure ABS and brake warning lights are functioning; address any warning indicators immediately.
• Maintain pads/shoes, rotors/drums, fluid or air systems, and software updates for electronic braking components.

Proactive checks and correct technique preserve braking performance and can significantly reduce stopping distances in critical moments.

Summary

The “three brakes” most commonly refers to service, parking, and emergency braking. In heavy vehicles with air brakes, these are three distinct systems by design; in passenger cars, the parking brake doubles as the “emergency brake,” while redundancy, engine braking, and electronics provide the third layer of protection. Across road and rail, the principle is the same: one system for everyday stopping, one for holding stationary, and one for safely handling failures or urgent stops.

What does a 3 mean on brakes?

At 3 millimeters the brakes are just about worn out and should be replaced.

What is the 3 form of brake?

This word is a regular verb. Hence, its 1st, 2nd and 3rd forms are brake, braked and braked.

What are the three types of brakes?

In fact, there are different types of brakes between vehicles and within the brake systems. Disc, drum, anti-lock, and emergency brakes, oh my!

Which brakes stop the car first?

They all work at the same time when you put your foot on the pedal, the front brakes give more effort than the rears, and the parking brake only applies on the rears, but those are the only differences.