St Helens Group of Advanced Motorists

Anti-Lock Braking System

Corners and bends are hazards that are encountered on most journeys and must be negotiated safely. The System of Car Control is applied to these road features, but the way it is applied depends to some extent on road speed.

Bends - National Speed Limit Zones

The approach speed is generally high and consequently good forward observation alerts you to the bend in good time (Information). Consider a single carriageway road. As you approach a right hand bend position yourself towards the left hand side of your lane so that you can improve your view of the road ahead. However, only do so if there are no nearside hazards such as pedestrians, cyclists or roadside debris. For left hand bends position yourself towards the right hand side of your lane but without driving on the white centre line. However, be prepared to move back to a central position if there is oncoming traffic or if you could mislead following traffic, or other road users, of your intentions. If necessary, reduce your speed on the approach, by deceleration or by braking if a substantial reduction in speed is required. Whatever method is used, use your mirrors (information) before reducing speed and ensure the speed reduction is smooth. When you have the correct speed for the bend then, if necessary, select a lower gear for that speed.

You are now in the correct position, travelling at the correct speed and in the correct gear. You should be driving at a constant speed towards the bend. A good rule of thumb is that, after the gear change, there should be at least 2 seconds between your hand returning to the steering wheel and your turning of the steering wheel to steer through the bend. If you are on a left hand bend with no pavement, then sound your horn to alert pedestrians to your presence (give information). As you drive through the bend you will need to increase the pressure on the accelerator pedal slightly to overcome the natural tendency of your vehicle to slow down on the bend. In effect, you are accelerating slightly through the bend but your road speed remains the same throughout (called driving at constant speed). This will ensure an equal weight distribution on all four tyres - increasing vehicle stability. When you reach the central point of the bend (the apex), the view of the road ahead will quickly improve. As you start to straighten the steering you can begin to increase road speed and accelerate away from the bend - provided there are no further hazards or speed restrictions. Check your mirrors before increasing speed (information).

Bends - 30mph Zones and Less

The 'System' as outlined above is applied with the following additional points. At these 'low' speeds there is generally no advantage in positioning to improve observation. There will be an increased likelihood of road users nearby so that changing position on the approach to a bend is more likely to mislead. Assuming a single carriageway road, adopt and maintain a central position in your lane on the approach and through the bend. However, be prepared to change position for safety - for example, to give more clearance between you and oncoming traffic or between you and vehicles parked on the bend. If lane widths are relatively wide, avoid any temptation to shorten right hand bends (cutting) which could put you into conflict with oncoming traffic.

Bends - Between 30mph and National Speed Limit

The System is applied but the procedure for positioning will depend on the situation. Generally, as road speed increases then more advantage can be gained by positioning to improve observation.

Corners - All Speed Limit Zones

Corners are generally right angled and occur at junctions. Right hand turns at corners tend to be from a minor road to a major road and consequently they will be negotiated from a rolling or a standing start from a give way or stop line. Left hand turns at corners tend to be from a major road to a minor road so that the initial speed of approach can be anything up to 70mph. Whatever the initial speed of approach, most left hand corners will require approximately the same speed to be negotiated safely. The corner is observed at the earliest opportunity (information). Other road users needing to know your intentions are alerted by your left hand signal, and perhaps a slight change of position towards the left hand side of your lane (give information and position). Check you mirrors and then reduce your speed (probably by braking) until you have acquired the safe speed for the corner. Once you have the correct speed, remove your foot from the brake and select a lower gear (probably 2nd gear), if required. If you are going downhill into a corner, it is acceptable to change gear with the brakes applied - provided that most of your braking has been done before the gear change. As you enter the new road watch out for pedestrians walking across your path and for speed limit signs. As you start to straighten the steering you can begin to increase road speed and accelerate away from the corner - provided there are no further hazards or speed restrictions. Check your mirrors before increasing speed (information).

The limit point of observation

As you approach a bend you will see the road disappearing to the left or right. At the point where the road disappears, pick out one feature on each side of the road - as seen from your vantagepoint. As you get nearer to the bend, these two features will appear to get wider apart. The slower they separate, the tighter the bend. The faster they separate, the more open is the bend.

A ratio of 0% means the wheels are turning freely, whereas a ratio of 100% means you're experiencing one of the most terrifying moments of your life, you're skidding. Now we have looked at the numbers and understood what happens to the car when we stop, how does ABS help? Tests have shown that if you want to stop safely and quickly you need to maintain a slip ratio between 10% and 30%, this has been done in the past by the use of cadence braking. This is when you pump the brake pedal, by fully releasing the brakes and then reapplying them. With ABS, sensors on the wheels and a computer calculate the slip ratio and maintain the optimum braking level for you by automatically pumping the brakes just like cadence braking only a lot faster. This will bring the car to a halt generally within a minimum stopping distance (depending on lots of factors) but more importantly it allows the driver to keep directional control of the car in an emergency stop situation. Those of you who been on a skid pan will know that in a front wheel skid you loose control of your steering, and it's not a nice feeling.

Some food for thought. If you have ABS on your car, do you know what it feels like when it operates? One problem that arises with ABS is that people only use it in an emergency and when they feel the pedal moving up and down under their foot they panic and take their foot off the brakes. It's also worth knowing that when snow or gravel forms a wedge under your front wheels it can sometimes confuse the ABS system and your stopping distance may increase.

Remember, drive safely and hopefully you will never need your ABS.

Disclaimer: Driving is never a black and white activity, but full of grey areas, therefore neither I nor my fellow Observers in the St Helens Group of Advanced Motorists are liable for any consequences you may experience as a result of reading our advice. You are the driver. You should be in control of your vehicle at all times.