Limit Point & How To Use It For Bend Assessment

The Limit Point Analysis Method of Bend Assessment is one of those magical advanced road driving techniques that causes great excitement, even for the most seasoned of driver, when revealed to them. Cornering technique is one of the aspects motorists never get taught as a matter of course, and yet bend work is statistically one of the highest features of road crashes. Certainly, bends are places where many drivers end up falling off the road.

Effective cornering is something that only gets taught during an advanced driver training course, otherwise the way that people drive around bends is completed in quite a hit or miss manner. The methods used by untrained drivers are very much based on their own personal experience, which is built up through their own individual experimentation, and unfortunately through observing the behaviour of other drivers.

Cornering isn’t just about turning the steering wheel

The art of successful cornering is not merely a case of turning the steering wheel, but one that involves a whole range of other factors. How do you take a bend properly, effectively and safely? When out on the road with us we talk extensively about the forces acting on a car, and the effects a driver will have when doing certain things with the driving controls.

The subject of the poise and balance of the car becomes even more important here, as for a start, we do not brake or accelerate whilst cornering, because these actions will put the car out of balance, which we don’t want at a time when it is already dealing with the forces required to make the it travel around the bend.

To avoid braking in a bend we have to first get the car travelling at a speed at which it is going to negotiate the bend safely, and before we begin to apply any steering. This means we need to be able to accurately assess the severity of a bend before we get into it. But how do we know the speed at which we need to be travelling for any given bend before we are actually going through the cornering process?

Using The Limit Point is a Vanishing Point

The answer has a lot to do with something called The Limit Point, which in simple terms can be referred to as the use of the Vanishing Point.

The limit point is that last and furthest away little bit of the road surface that you can see before it disappears out of your range of view. Like looking at the horizon out at sea. It can also be the point where the road surface disappears around the corner. To use learn to use the process to assess a bend, have a go at this.

Take your car out on the road, preferably to a rural environment, and find a right–hand bend. Drive the car towards it and stop on the nearside of the carriageway at a distance of about 50–metres before the start of the curve. Make sure it is safe to stop though, as you do not want to become a hazard for someone else, or put yourself at risk.

If you study the view ahead you will note the nearside verge runs away from you on your left, and then curves to the right as it follows the line of the bend.

The Road Edges Will Meet in The Bend

Now run your eye along the off–side verge and you will see there will come a point where it will appear to meet the nearside verge, forming an arrowhead of tarmac. This arrowhead is what we refer to as The Limit Point, and is that last little bit of the road surface you can see in the distance.

In the diagram you will see we have marked this with the letter C, and the letter B marks the vanishing point of the nearside verge. Point A is your eye, and by looking forward through point B to point C, and because your view perspective from your driver’s seat will be somewhat two–dimensional, point B and C will appear to be one of the same.

These two will be at the tip of where the road surface takes on the shape of the arrow head, and it is this you will need to pay attention to as you move on to the next step.

As you drive towards the bend you will find is that the arrowhead shape of the road surface, when you are close enough, will begin to change, appearing to move to the right.

The way in which you use this is to chase the point of the arrow, but never so fast as to gain on it. If you are gaining on it you are travelling too fast for the curve. If you are losing ground to it, then you are travelling more slowly than you need to.

Watching the Limit Point is like pushing a door open in front of you

The opening view that you get from The Limit Point is a bit like standing in a hallway of a house and pushing a door open to a room in front of you, a door that swings away from you that is. As the latch–edge of the door swings into the room, more and more of the room interior is revealed. In the same way you will see more and more of the road surface ahead of you, and of the near–side verge of your bend.

Having seen the movement of the Limit Point,
approach the bend from further back

Now go back and drive the bend again. This time, begin your approach from much further away. This time you will note how point C will initially appear to be stationary. However, think about this.

If you were to drive along a straight road with a solid wall built across it, there would become a point when you would automatically begin to slow down, because unless you are suicidal, you will want to stop in sufficient time so as to avoid crashing into the wall. This works because your brain is telling you that if you keep going towards the wall at your current rate of speed you will hit it, and that is going to hurt.

It’s about making an unconscious calculation for a closing distance

In this scenario you make an unconscious calculation using the rate of closing distance as part of your formula to make sure you begin applying your brakes early enough so as not to come to any harm.

This is your basic instinct to survive at work, and become more focussed the faster you approach the wall. You would become extremely sharp with your judgement if you had to drive at your wall and bring the car to a stop inches away from it in as short a time span as possible.

Use the arrowhead on the road as your wall. If you find you are catching up with it, slow the car down. If it is moving at the same rate as the speed of your approach, then you are travelling at the optimum speed for the bend.

If the Limit Point moving away from you then you may perhaps increase your speed a little (all due consideration being given to safety of course). The sharper the bend the nearer you will get before point C starts to move, so the more you will have to reduce your approach speed if you are going to navigate the bend safely.

The Link Between Your Accelerator Pedal & The Limit Point

Once the road straightens out, point C will zoom off into the distance and you can then accelerate to an appropriate speed according to the range in visibility and conditions. To help you to put this all into perspective, imagine there is a piece of string tied to your accelerator pedal, with the other end tied to The Limit Point, e.g. point C.

As the distance between you and The Limit Point continues to close down, your imaginary length of string will go slack, thus releasing the pull on the accelerator pedal. This of course slows you down.

However, if the distance between you and The Limit Point had remains constant, the string would have kept your accelerator pedal in the same position. If The Limit Point runs away into the distance, so the string pulls the accelerator pedal towards the car floor, causing the car to increase speed.

Once you have entered the bend that bend is dealt with
and you are now working on the next one

As the bend finishes, and you accelerate away, look into the distance for the next bend, and the next Limit Point, and start planning for that one way before you get there. This way you will begin to overlap your planning, and when the method is perfected, you can drive through a series of bends whilst dealing with one after another after another, always driving at the optimum speed for the road throughout. Remember, as soon as you are entering the first bend you have already dealt with it and therefore should already be planning for the next.

Beware of the double apex

However, a few words of warning here. Once The Limit Point has told you that your speed is appropriate for the corner, don’t take that information for granted. You have to keep watching, as you need to be wary of the bend that has a double apex, or dog–leg.

Another word of warning is to make sure you use the road–edge and not the hedges that may be set back from the road edge (refer back to diagram), because when a hedge line sits back from the carriageway, it may give a false reading, or the hedge may not follow the arc of the bend — also giving a false reading.

Reading The Limit Point of a bend accurately takes a while to tune into

Once you do get the hang of it you can drive along any piece of road and use this method at every twist and turn, and will find that you can make good progress even if you have never driven that road before. The method works just as well for left–hand bends as well as right, and when used effectively it will mean that you will never get caught out by a bend or corner again.

When you take a car out on a public road, unlike the track driver, you cannot say with any confidence that you know every little ripple, crack and oily spot within that environment? The local farmer could have parked a tractor around the next bend – complete with plough attached? Also, you don’ know the ability level of those sharing the road with you, or their purpose of being there

On The Public Road You Never Know What Will Happened Next

Always expect the unexpected, as the public road environment will change dramatically, sometimes over a period of a few minutes, so you can never be sure what is going to happen next. Base your assessment on what can be seen, what can’t be seen and what circumstances may reasonably be expected to develop. Always be in a position to stop within the amount of road surface you can see at any one moment, i.e. the distance between you and The Limit Point – as in the space between the horizon on the tarmac and the front of your car.

If you have got the bend right you will negotiate it at the most appropriate speed, with the most appropriate gear engaged, will be on your correct side of the road and be able to remain there. If you take all the advice on board that you have seen on this page you should never be in a situation whereby you have got out of your depth.

Julian Smith
Ride Drive Limited

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This page was last updated
Thursday, 27-Jan-2011

Limit Point & How To Use It For Bend Assessment