They do that in order to average the speed out and in turn try to prevent the traffic 'elastic banding', ie; very fast, then, for no reason, very slow, etc.

M25 is a classic case in point

 

I agree with what your saying re. the signs - can be very frustrating but they obviously do it for a reson!

Don't know whether I'd go to the extent of ignoring them though - apparently (according to some programme I watched ages ago...... ) the speed cameras on the M25 are hooked up to the signs in question, hence, if the sign says 50, and you ignore it - you get a nice photograph of your car taken!

Kelvin

 

We've all been there.... going along the motorway there doesn't seem to be anything wrong but up ahead there’s one of those temporary signs displaying 50 or fog or something else. You slow down and keep an eye out for the reason behind this restriction, next thing you know you see another one of those signs that says END

Why the sign then Why was I instructed to slow down for nothing Do the people who monitor the M25 actually know what's going on or do they just think, " I know it'll be a laugh why don't we get everyone to slow down and bunch for nothing" HA HA very funny NOT!

Okay I'm going OTT but I'm beginning to ignore these signs because they don't mean anything you get told there’s fog when there is none, you get told to slow down for no reason, you get told that the outside lane is closed off when it isn't.

If the authorities want people to take notice of these signs then they have to stop crying wolf.

 

I beleive that the signs in the central reservation (the square black things) are adviseary limits only - so I think you can drive to the national speed limit if conditions are suitable. The signs on the gantries on the M25 are "variable speed limit" signs and you are required by law not to exceed the displayed speed.

StuartH - can you confirm/deny any of the above coz i may be talking pants.

 

I was under the impression that these limits were no longer advisory, they are now mandatory.

Stuart?

 

Matrix signals (the square black things) are compulsory speed limits (see rules 229 - 232 of the Highway Code)

<I><B>Rule 231 - Amber flashing lights:</B>
These warn of a hazard ahead. The signal may show a temporary maximum speed limit, lanes that are closed or a message such as 'Fog'. You must adjust your speed and look out for the danger until you pass a signal which is not flashing or one that gives the 'End' Signal and you are sure it is safe to increase your speed.</I>

The system on the M25 GATSO's is interlocked with the matrix signals therefore adjusting the camera trigger speed.

[This message has been edited by Stuart H (edited 11 December 2000).]

 

Staurt

How is it decided that a signal is required? It seems that these signals are randomly changed for the hell of it.

 

The speed of traffic is monitored by a number of measures back in the control room, who will activate the signals. The main reason for seeing a temporary limit then an end is as Fosters says, to keep the average speed of traffic at a safe level. Patrolling officers can also have them activated.

The control room staff do not (contrary to popular opinion) have all the speed limits on pieces of paper and pull one out of a hat!

 

I'm sure it wouldn't be a hat they’d use anyway, it would probably be something with a slightly smaller opening.....