Use of speed

How do we know what speed to drive at?

We must consider two factors:

The legal speed limit

Choosing a safe top speed

How do we identify the speed limit? We can look out for change of speed limit signs. When we see two signs on both sides of the road, this is the start of a new speed limit.

If the new speed limit is higher than our current speed limit, we must not speed up until we have passed these signs.

Likewise, if we are on a road where the new speed limit is slower than our current speed limit, we must reduce our speed to the new speed limit before we reach the signs.

When we see a single speed limit sign on it's own, this is called a "repeater sign" and it reminds us of the speed limit for that road.

20mph zones are becoming more widespread, we will often see these near schools and busy pedestrian areas.

This sign means "national speed limit". We would expect to see this sign at the start and along either a single carriageway or dual carriageway.

We have already mentioned how we identify a single or dual carriageway, but just to recap, it's nothing to do with the number of lanes.

A single carriageway is one piece of road with traffic travelling in both directions.

A dual carriageway are two separate roads divided by some kind of central barrier.

The national speed limit sign is used as the speed depends on the type of vehicle being driven.

The national speed limit applies unless other signs tell us otherwise.

What if there are no signs telling us the speed limit? We must look for other clues, the speed limit for built up areas is 30mph.

We must remember, these are speed limits, not targets. So how do we choose a safe speed?

There are several factors that we need to assess:

What you can (or can't see) in front of you

Other road users

The weather (how it effects our visibility)

The surface of the road

We have already mentioned the 2 second rule, the pace of traffic ahead can decide your speed for you.

If there is no traffic in front of us, we need to use our own judgement to choose a safe top speed. We need to start asking the question "what if". Look at the image below, "what if there was a broken down car just around the corner, what speed would allow me to stop in time?

Generating worst case scenarios is a good way to choose you safe top speed. If the picture ahead looks good, we can speed up, if it starts to look bad, start to slow down.

Other road users can also influence our decision on what speed to drive.

How would you change your speed in these situations?