Correct use of Speed
Speed Limits
Speed limits MUST be observed at all times. It is a criminal offence to exceed the speed limit, so you must know the speed limits as described in the Highway Code. If you don't know them, how can you observe them!
A speed limit is simply a maximum legal speed. It is not a recommendation or a target. A good driver will drive at a speed appropriate to the road, traffic and weather conditions, within the speed limit.
Making Good Progress
As you drive along the road, one aim should be to make good progress within the speed limit. On Test, your examiner will look for a brisk, lively drive where conditions permit, up to or at the speed limit, but (of course) not exceeding the posted speed limit. Also remember that your examiner is going to be looking for an 'Eco-Safe' drive, so don't accelerate too harshly, and try to use engine braking where appropriate.
There will be times when you will need to travel more slowly, or even stop, to deal with hazards, and these should be dealt with efficiently, enabling you to proceed promptly when safe and convenient to do so.
Our goal here is to give you the ability to get where you are going quickly and safely.
Judging safe speeds
One key guideline on the use of speed is this :
Always make sure you can comfortably stop, on your side of the road, within the distance you can see is clear ahead.
One invaluable aid to this is knowing your emergency braking distances (from The Highway Code), and being able to visualise them in terms of length of road. To be safe, reckon on allowing twice the emergency stop distance, as this gives you the option of a gentle brake, and also allows for the stopping distance of on-coming traffic travelling at a similar speed.
For example, on a National Speed Limit single carriageway (60mph limit), if you can see the road ahead is clear for 100m, in theory you will be safe at the speed limit (73m stopping distance), but dropping to 50mph would be appropriate (53m stopping distance - around half the distance you can see ahead).
This method is particularly useful when approaching curves and bends...as the view ahead decreases you should slow down in proportion, and exiting the bend you can proportionately increase your speed as the view ahead improves.
This is known as "Limit Point Analysis", because you are constantly analysing the distance of the furthest point you can see ahead (the Limit Point) to calculate what would be a safe speed.
General Advice
Around town, with (normally) a 30mph speed limit and more road users present, consider the following three criteria for slowing down:
1) When your view ahead is obscured or obstructed.
2) When there is less space available.
3) When you have more work to do (eg steering).
The bigger the problem (eg less view ahead or narrower road) the slower you should be travelling. Also the problems are cumulative, so if you have a poor view on a narrow road, say, go even more slowly. If at the same time you need to steer a lot (eg around parked cars), go slower still.
The advice above is to allow for potential hazards, and is in addition to the care you will need to exercise when dealing with identified hazards, such as pedestrians crossing the road, or on-coming traffic.
If in doubt, be prepared to slow down. This will enhance safety, and is likely to give you more time to analyse the hazards ahead. Remember to check your mirrors before any change of speed, as part of the MSM routine.