As of last week, work has started on giving Bristol it's very own mini-m25. Where the M4 and M5 cross each other to the north west of the city the Highways Agency is created a section of what it calls 'Managed Motorways'.

Managed Motorways is Highways Agency Marketing speak for basically two changes:

• Variable Speed Limit Cameras
• Use of the Hard Shoulder

Now, the first of these, will be erected over the motorway in gantrys and, just like the M25 you'll have a specified speed limit, possibly just 30mph at times and a speed camera sitting there enforcing it.

My first problem with this is the amount labour that must go into monitoring the traffic flow and adjusting the speed on the cameras to match, means that the more they install these cameras, the more staff they need, the bigger their budget becomes etc, (jobs for the boys).

My second but larger gripe is with the hard shoulder idea. It's there so that incase of an accident, emergency vehicles can reach those who need help.

When do most accidents occur? Peak times.

When will the Hard shoulder be filled with slow moving or stationary vehicles? Peak times!

Ill agree use of the hard shoulder is silly. I would rather sit in traffic for 20mins than them open up the hard shoulder for traffic.
I would expect little to no man hours are used to control the speed limits though? strikes me as something very easy to manage using a relativity simple counting/speed algorithm?

They have done this to a little stretch on the M6 around where I live but I rarely see anyone keeping to the set speed limit. It has probably been about a year since they have gone live so are they all going to be getting tickets or do they know something I don't?

It works brilliantly on the M42 - it creates an additional 33% capacity and IF there's an incident/accident, it's reverted back to three lanes instantly

The variable speed limits also work very well - it's far better to be travelling at a steady 40-50mph, than being allowed to reach 70+, only to create a concertina effect and then end up stationary for five minutes, for no apparent reason

The M42 was the pilot for this system and it has been SO succesful that it's being regarded as a model for other sections of motorway

So it's all YOUR fault Nigel

I had reservations when this was installed on the M6 up by Birmingham, but I have to say that it works well, and the queues have been less than they used to be.

Whether it justifies the disruption caused whilst doing the work is another matter....

I'm with Nigel - I think the sections of motorway that I've been on with managed speed limits have generally been very effective. Monitoring is probably done largely automatically using the same sort of technology as TrafficMaster/Average Speed Cams use. I can't speak for hard shoulders but, if Stan is to be believed (at the extremes of possibility, I know) you don't want to stop on a hard shoulder anyway.

They won't need extra staff for this Truffers, The control room staff simply set the limit via a touchscreen monitor and the cameras react to the input; if they set the limit to 40mph the camera recognises that.

There should also be "refuge" areas every 800m (from memory) designed to accommodate everything up to HGVs so that they can safely be worked on off the hard shoulder.

I did do a write up about this a few years ago because I was invited to give feedback at a planning meeting about this idea. My feedback was mainly negative, although I could see the advantages I could see the bigger dangers, as well as the smaller ones, for example the amount of debris that ends up on the hard shoulder is one of the reasons we had a speed limit for hard shoulder running due to the risk of punctures/debris strikes. I've lost count of the number of punctures I've picked up on the hard shoulder! At the time they said they'd be sweeping the shoulders more often but I wasn't convinced at all.

My biggest concern was how quickly motorists would respond if the shoulder was closed suddenly, especially if I was standing on it dealing with an incident!

Well it's going to take 2 years for the work to be completed (assuming it remains on schedule), so i'm sure that people will marvel at how free flowing the traffic is once work is completed.

Mainly because they've forgotten what the traffic was like before all the cones appeared.

Agreed, it's brilliant. Some days it was an average of 15-20mph during the evening rush. Now it's at least 50mph