Slowing down and stopping your heavy goods vehicle (HGV) in a controlled way is vital for good driving: it reduces wear and tear on your vehicle, saves fuel and keeps you and other road users safe.
The distance your vehicle will take to stop depends on how fast you’re going, the road and weather conditions, and the size of your vehicle.
- The faster you’re going and the larger your vehicle, the longer it takes to stop.
- It takes longer to stop in wet or icy conditions.
The stopping distance is made up of 2 parts:
- thinking distance – the distance you travel from when you decide to brake to when you start braking
- braking distance – the distance you travel from when you start braking until your vehicle stops completely.
The weight of an HGV makes the braking distance for an HGV much bigger than that for a car travelling at a similar speed, so you’ll need to allow extra time and space to stop safely. You can see the typical stopping distances for cars in The Highway Code (GOV.UK).
When you need to brake, make sure you are aware of the road users around you. Check your mirrors and signal if necessary before you begin braking.
Anticipating the need to brake will help you brake smoothly, progressively and safely: watch out for things around you that you might need to slow down for, such as pedestrian crossings or cars pulling out of junctions. It’s important to try to plan your braking so you only use the brakes when the wheels are straight. Braking while you’re turning can cause the vehicle to skid.
Harsh braking can destabilise the load on your vehicle, which could lead to the load being shed or will at least need you to stop and re-secure the load before you can continue on your journey. On articulated vehicles it can also cause jack-knifing (where the tractive unit is pushed forwards by the semi-trailer) or trailer swing. You can avoid these situations by braking, steering, accelerating and changing gears smoothly.
Like cars, smaller goods vehicles usually have hydraulic braking systems. Large vehicles generally have air braking systems or air-assisted brakes (hydraulic system with air assistance).
If you need to make an emergency stop in a vehicle with hydraulic brakes, you may need to pump the brakes (called cadence braking) to avoid locking the wheels. When you have done this, you’ll need to find somewhere safe to stop and check the hydraulic system before you continue your journey to make sure the brakes still work properly.
Anti-lock braking systems (ABS) can help you brake safely and effectively by helping to prevent skidding but they will not shorten your stopping distance. If your vehicle has ABS and you have to brake heavily in an emergency, apply maximum force to the brake pedal and maintain this force: the ABS should stop the wheels locking up. Do not pump the brake pedal because this reduces the effectiveness of the ABS.
Endurance braking systems, also known as retarders, help control a vehicle’s speed without using the wheel-mounted brakes. These systems reduce the wear on the service brake and avoid the risk of brake fade when you’re driving down long or steep hills. They work by applying resistance to the rotation of the vehicle’s drive wheels rather than to the road wheels.
There are several different types of endurance braking system.
- electric – uses a magnetic field to slow the axle, transmission or driveshaft
- engine-driven – changes when the engine cylinder exhaust valves open so less compressed air is available to drive the piston back down, which slows the engine
- exhaust brakes – the exhaust pipe is restricted by a valve so raises the pressure in the exhaust system and forces the engine to work harder on the cylinders’ exhaust stroke, similar to the engine-driven system.