The requirement to have a CDL in order to drive a CMV (Commercial Motor Vehicle) has been mandatory since 1992, however a CDL by itself is not enough. Depending on the type of vehicle a driver operates, he or she may still be required to undergo testing for one or more CDL endorsements. Normally, the most common type of endorsement required is the one for air brakes. Air brakes are the most efficient and effective type of braking system for large, heavy vehicles but their use and maintenance requires special knowledge on the part of the commercial driver.

Air brakes normally consist of three different braking systems: the service brake, parking brake, and emergency brake. The service brake system operates when the brake pedal is used during normal driving. The parking brake system operates when the driver uses the parking brake control. The emergency brake system kicks in to stop a vehicle during brake system failure, and utilizes parts from both the service brake and the parking brake.

Knowing first what kind of air brake system a driver will operate should be top priority. If a driver is going to pursue an air brake endorsement, these are the things he/she should know first:

• Air Brake System Parts
• Dual Air Brake Systems
• Inspecting Air Brakes
• Using Air Brakes

Air Brake System Parts

Air brake systems are not standard on all vehicles; there are different types of systems depending on the make of the vehicle, and the date it was manufactured. There are many parts to an air brake system, and having an intimate knowledge of what each part does will make it easier for a driver to diagnose a potential problem. There are parts that are specifically designed to alert the driver if there's anything wrong, and knowing these parts is the key to maintaining proper air brake functionality in a vehicle.

Dual Air Brake Systems

Most of the bigger vehicles utilize a dual air brake system connected to one set of brake controls. These systems, designed for safety, control two separate sets of brakes for the front and rear axles. Maintaining proper air pressure in both the primary and secondary system is key to maintaining harmony in the dual system. Should the pressure in either system drop to 60 psi or lower, it will turn off that brake system and it will take longer for the vehicle to come to a complete stop. Should this happen, the safest option is parking the vehicle in the nearest available stop and getting the brake systems fixed.

Inspecting Air Brakes

There are more parts to inspect in a vehicle with air brakes than one without, and knowing how to properly inspect the parts for any possible trouble is key to maintaining safe vehicle operation. Since air brakes operate on compressed air, there will be several gauges and warning lights in the vehicle that would tell if air pressure is at optimum working efficiency. If there is any suspicion that the system is not working properly, the driver needs to take immediate action to prevent longer braking or the need to rely on the emergency brake due to failure of the system.

Using Air Brakes


Knowing how to use the braking systems properly is the first step in making sure that the air brake system(s) will last for a long time. Knowing how to perform emergency stops while the ABS (Antilock Braking System) is on, remembering to use the parking brake system, and knowing the proper stopping distance for the vehicle a driver would be operating are what makes for safe operation of vehicles with air brake systems.

In order to get proper training for air brake endorsement, a driver must pass a written exam, and perform specific maneuvers on the vehicle they plan to operate, in order to gauge their knowledge about air brake systems.

Learn more about how to get you CDL or take a FREE Air Brakes test at TestQuestionsAndAnswers.com.

Labels: air brakes, cdl, CDL endorsements, CDL practice test, commercial drivers license, commercial truck drivers, commercial vehicles

Standards for testing and licensing Commercial Motor Vehicle (CMV) drivers are developed and issued by The Federal Highway Administration (FHWA). These standards mean that states can only issue Commercial Driver’s Licenses (CDLs) to CMV drivers if the drivers pass knowledge and skills tests that relate to the type of vehicle the driver will be operating. CMV drivers have been required to have CDLs since April 1, 1992.

Drivers may have a commercial drivers license (CDL) with certain endorsements or restrictions. Endorsements mean that a driver is qualified to operate a particular type of vehicle. Restrictions mean that a driver is not qualified to operate a particular type of vehicle. If a driver fails the air brake component of the general knowledge test or performs the skills test in a vehicle that does not have air brakes, the driver’s CDL will indicate that the driver is restricted from operating a CMV that has air brakes.

How Do Air Brakes Work?

Air brakes use compressed air to make the brakes stop the vehicle. There are actually three braking systems in the air brake system: service brake, parking brake, and emergency brake. The service brake system applies and releases the brakes when the brake pedal is used during normal driving. The parking brake system applies and releases the parking brakes when the parking brake control is used. The emergency brake system uses parts of the service and parking brake systems to stop the vehicle in a brake system failure.

Stopping distance is greater on vehicles with air brakes because with air brakes there is an added delay when stopping. The delay comes from the time required for the brakes to work after the brake pedal is pushed; it takes one-half second or more for the air to flow through the lines to the brakes. Drivers of CMVs with air brakes need to be aware of brake lag distance so they can allow for additional stopping distance.

What Do CDL Drivers Need to Know about Air Brakes?

All commercial motor vehicle operators must have knowledge of air brakes, unless they have a restriction on the CDL indicating that they are not qualified to operate a CMV with air brakes or have your CDL Air Brakes endorsement. The driver must have knowledge of:

• Air brake system nomenclature


• The risks of a contaminated air supply


• The consequences of severed or disconnected air lines between the power unit and the trailer(s)


• The implications of low air pressure readings


• A method of conducting a safe and accurate pre-trip inspection


• Procedures for performing en-route and post-trip inspections of air actuated brake systems, including the ability to identify defects which may cause the system to fail

Labels: air brakes, cdl, CDL endorsements, commercial drivers license