What is an anti-lock braking system (ABS)?

What is ABS? A guide for fleet managers

ABS stands for anti-lock braking system. It is a safety feature that prevents wheels from locking up while braking to avoid skidding.

ABS systems consist of computer sensors and solenoid valves which monitor wheel speed. The ABS senses when wheels are about to lock during an emergency braking situation and releases enough brake force to maintain traction with the road surface. The ABS allows drivers to retain more control of the vehicle by modifying brake pressure.

Without the ABS safety system, drivers can lose steering control of their vehicles while skidding and potentially overturn. ABS is particularly important for controlling wheel speed on loose gravel or slippery surfaces. However, ABS doesn’t necessarily shorten a vehicle’s stopping distance. On most surfaces, a vehicle equipped with ABS will likely stop faster than one without. But on slippery surfaces, ABS activated by hard braking may increase stopping distance while allowing drivers to keep steering control.

In the United States, federal regulations mandate that all new cars, tractor trailers, and minivans manufactured in or after 2012 must be equipped with four-wheel anti-lock brake systems (ABS). This requirement aims to enhance road safety by improving braking performance and maintaining steering control during emergency braking or slippery conditions. To determine if your vehicle has ABS, consult an owner’s manual or look for an ABS light on your vehicle’s dashboard.

How do anti-lock brakes work?

Before anti-lock brakes, drivers were taught to “pump their brakes” when they start to skid on slippery roads. Today, ABS does this for drivers, only faster and more accurately.

The ABS comprises wheel speed sensors, an electronic control unit (ECU), valves, and a pump.

1. The system relies on sensors that constantly monitor the speed of the vehicle’s wheels.

2. The sensors send data to the ECU. The ABS controller is always looking out for rapid deceleration, an early signal for wheel lock.

3. When the ABS controller detects rapid deceleration or an emergency stop, it uses a valve in the brake line to reduce pressure to the wheel. This causes acceleration.

4. The controller will then use a pump to increase pressure again until the wheel decelerates again. However, because of the ABS, the tire slows down at the same rate as the vehicle.

When the anti-lock brake system is working, drivers will feel the brake pedal pulsing. This rapid opening and closing of the valves—or the brakes “pumping”—helps the driver maintain control of their vehicle.

Types of ABS brakes

Advancements in automotive technology have led to the developments of various anti-lock brake systems (ABS), each designed to enhance vehicle safety and control during braking. These systems differ in how they monitor and manage wheel lock-up to prevent skidding. 

• Four channel, four sensor ABS. This system has a separate speed sensor and valve on all four wheels. It’s considered the best system because it monitors individual wheels, ensuring maximum braking force. The ABS will only pulse on the single wheel that’s about to lock up, giving drivers better traction control and minimizing loss of control.

• Three channel, three sensor ABS. This setup is found on pickup trucks featuring four-wheel ABS. In this system, both front wheels have individual valves and speed sensors. The rear wheels share a valve and one speed sensor in the rear axle. Because the rear wheels are monitored together, both wheels must lock up to trigger ABS.

• One channel, one sensor ABS. This system has one valve and one speed sensor to monitor all four wheels and is located in the rear axle. It’s typically found on pickup trucks that have rear-wheel ABS.

Electronic Stability Control (ESC) builds on the foundation of ABS by adding additional sensors and functionality. ESC incorporates ABS with a gyroscopic sensor and a steering wheel angle sensor to monitor the vehicle's direction and the driver's intended path. If the system detects a discrepancy, such as the car skidding or losing traction, it automatically applies the brakes to individual wheels (up to three in advanced systems) to help the driver maintain control.

How do ABS systems help improve trailer operations? 

While ABS systems are often associated with passenger vehicles, they also play a critical role in trailer operations. ABS in trailers are designed to improve braking performance and minimize incidents, especially in challenging driving conditions. ABS systems help trailers:

1. Prevent wheel lock-up: ABS prevents trailer wheels from locking during hard braking, reducing skidding and maintaining stability, especially when towing heavy loads.

2. Enhance maneuverability: ABS ensures directional control of your vehicle and trailer on slippery roads by optimizing braking pressure and allowing wheels to rotate.

3. Prevent jackknifing: Jackknifing occurs when the trailer swings out and forms an angle with the towing vehicle. ABS helps to minimize the risk of jackknifing by preventing wheel lock-up, keeping the trailer aligned with the towing vehicle.

ABS is essential for trailer safety, but limited visibility can make it difficult to know the full status of your ABS system. Without a telematics solution, drivers and fleet managers would have to access ABS fault information by physically checking the trailer or spotting the ABS light. A trailer’s ABS light may turn due to something as simple as a defective power source, or it may indicate a more serious malfunction. Without comprehensive visibility into trailer performance, it's hard to know if it’s an urgent issue that requires immediate attention. A faulty ABS system can increase the risk of rollovers, jackknifing, extended stopping distances, and ultimately may result in downtime and on-the-road incidents. 

Today, innovative organizations are looking to advance telematics technology, such as Samsara’s Smart Trailers solution, to improve the efficiency, compliance, and safety of their ABS and trailer operations. With Samsara ABS Monitoring, you can gain full visibility into ABS issues to:

• Streamline proactive maintenance: Save time by pinpointing the exact ABS fault, enabling technicians to monitor brake, tire, and power issues across your trailer fleet and address them proactively before they escalate.

• Ensure trailer safety: Identify and address ABS safety risks before accidents occur with insights into critical trailer systems, including brakes, tires, and power. Real-time alerts to the back office and drivers ensure quick and efficient resolution of potential issues.

• Avoid CSA violations: Improve your CSA score and easily pass inspections with full visibility into active ABS faults and tire issues.

To learn more about how Samsara can help you run a safer, more efficient trailer operation, explore our Smart Trailers solution and speak with our team today.