Within the Advanced Driving Course, we teach a technique for reading the road called the limit point of vision. This is an invaluable tool which I’d like to talk about it in a little more detail. If you’re new to advanced driving, I hope you find this interesting and useful; if you’re a stalwart of the advanced driving community, a refresh never goes amiss.
In nineteen-eighty-something when my father taught me to drive, I remember him telling me: “imagine there’s a skip out of sight around every corner”. Whether he knew it or not, he was teaching me the limit point of vision.
The Advanced Driver course logbook states: “The limit point is the furthest point to which you have an uninterrupted view of the road surface as it disappears around a bend or over a brow. It is the point where the two edges of the road appear to meet. On a left hand bend you should treat this as where the left-hand verge appears to meet the centre line”. Other Observers I have discussed this topic with describe the limit point as: “the furthest point you can see to be clear on your side of the road”, which is far more succinct.
All of these definitions (I still think of the skip as it focuses the mind somewhat) are fairly static in nature, written as if we (the driver and the limit point) are two fixed points. However, nothing could be further from the truth when it comes to reading, interpreting and reacting to the limit point; our car is moving, and as our viewpoint changes, so does the appearance of the limit point.
The biggest visual cue we receive is the change in the gap between where we are and the limit point as we travel down the road; we can use the change we observe in the gap as a guide to how we should react:
If the gap is reducing (the skip is getting nearer), then we need to be considering reducing speed, asking ourselves, “can I stop in the distance I can see to be clear on my side of the road?”, if the answer to this is no, we are driving too fast and should have slowed earlier.
If the gap is staying constant, then we can keep going at our current speed (assuming we can stop in the distance we can see to be clear).
If the gap is increasing, then the bend is opening up (there is no skip!) then we can think about accelerating (assuming there are no other hazards to consider).
The golden rule is that you should always be able to stop in the distance you can see to clear on your side of the road.
Until next time…
David.