Managed Motorways catch thousands of speeders

MikeB

Managed Motorways with variable speed limits have been in action in the UK for some time now. Starting with the M25 around the M4 intersection the overhead gantries sprung up sporting speed cameras. The variable speed limits were designed to slow traffic and help control the traffic flow. Initially the speed cameras were only active when there was a speed limit in force.

Now as the managed motorways have evolved into Smart Motorways we are seeing new styles of camera being installed, some sections are controlled by the average speed cameras, others by the newer HADECS, and the traditional gantry cameras still remain. Not only are there more and differing types of camera but some are also active at all times and not just when there is a speed restriction in place.

Drivers in the Bristol area have been finding this out the hard way, according to the BBC, where some 1,500 tickets have been issued in the first two weeks of operation. Although the works had been finished in January the cameras were only activated recently. Most of the offences were committed when there was a variable speed restriction in place. When there was no restrictions 70 drivers were ticketed in excess of 70 MPH and 3 over 100 MPH. In essence 1,430 drivers have no excuse as the speed restriction was clearly marked on every gantry.

This may be due in part to drivers disbelieving the signage, seeing a speed restriction when the road ahead was obviously clear. Often when driving on the managed motorways there are speed restrictions for no apparent reason, and this can lull drivers into a false sense of lack of danger and disbelief of the signage. This is especially the case when the signs say there is congestion ahead and reduce the speed limit and there is no indication of heavy traffic let alone congestion.

This could be caused by the Smart Motorway systems not being tuned correctly. The Smart Motorways use sensors to determine traffic flow and automatically set the speed restrictions. If the systems are not set correctly they can reduce the speed limit when there is no need. Drivers will note this and start to disregard the restrictions which could be the cause of the high number of tickets issued in the Bristol area.

The takeaway from all this is that even if the road systems are erroneously setting speed restrictions drivers still need to obey the signs or they will get a fine through the post. Also the cameras may be active at the permitted speed limit even when there is no sign illuminated.

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Mike Barrett

pdfbt40 · Occasional Visitor Joined: Jan 23, 2008 Posts: 56

Why do I get the feeling Managed/Smart motorways computer systems aren't optimised for quick traffic response but for a large hysteresis (time/distance delay). Accidentally that would lead to bias of inappropriate speed limits on clearing roads - Bang, revenue generator !

DennisN · Posted: Fri Jul 18, 2014 6:34 pm Post subject:

Guivre46 · Posted: Fri Jul 18, 2014 8:11 pm Post subject:

I think it means that the system responds quickly to traffic build up, but takes its time responding to its easing??

Or have you got your tongue in your cheek again?
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pdfbt40 · Occasional Visitor Joined: Jan 23, 2008 Posts: 56

Sorry, must reduce the technical jargon a bit. I'll try to remember.

Yes that's exactly what I mean, and explains why individuals complain of jams with no speedlimits and clear roads with 40mp.

In fact, the systems are more than able to be very sophisticated in anticipating increasing volume/queues and their clearing, much more than they are set to do.

Maybe that's like a decade or so back when somebody challenged a prosecution for speeding on M25. In court, he claimed there were no signs illuminated. The authority, at first made excuses why records were not available, eventually they produced a scruffy log book of dates but no entries, as previously claimed, of flow data, signs on/off, etc.

To really screw things up still needs people.

Kremmen · Posted: Sat Jul 19, 2014 5:56 am Post subject:

I can see the logic. I use the M25 western section regularly and everyone ignores the variable limit because it has been known for years that the cameras are not active.
As a result cars are steaming up to the back of a jam and adding to/causing a jam further along.

Back in 2004/5 when they widened this section they put in place a series of 40mph working cameras to protect the workforce. The result was that from the M3 to the M4 all cars did 40mph.

That is the only time I can remember where this section flowed smoothly every day of the week. If drivers followed the 40mph signs now then I believe the jam that starts (clockwise) where the M4 joins the M25 (J15) and (anticlockwise) where the M3 joins the M25(J12) then it would work better.
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pdfbt40 · Occasional Visitor Joined: Jan 23, 2008 Posts: 56

The original core of traffic flow modelling was taken from Chemical Engineering Fluid Flow programmes.

Vehicles are taken to be a compressible fluid, so density can increase as velocity falls (not retaining safe distance). Very quickly they were able to create 'phantom jams' with duration and size.

Unfortunately drivers don't know to obey the rules of the computer models, and whilst it can react to a full stop of an accident, it can't predict it.

DennisN · Posted: Sat Jul 19, 2014 8:03 am Post subject:

DennisN · Posted: Sat Jul 19, 2014 8:05 am Post subject:

pdfbt40 · Occasional Visitor Joined: Jan 23, 2008 Posts: 56

Oops. Sorry DennisN.

What I was trying to express, was that the Highway engineers didn't have to invent massive new knowledge to model the flow of traffic. In terms of the computer/mathematics, 'water hammer' in a pipe is the same sort of thing as a 'phantom jam' on a motorway.

DennisN · Posted: Sat Jul 19, 2014 11:25 am Post subject:

You can do the same thing using marbles in a bucket. But I've forgotten how.
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Dennis

If it tastes good - it's fattening.

Two of them are obesiting!!

253 · Posted: Mon Jul 21, 2014 9:07 am Post subject:

M8TJT · Posted: Mon Jul 21, 2014 9:22 am Post subject:

DennisN · Posted: Mon Jul 21, 2014 11:17 am Post subject:

Nah! Just a bucket and some marbles. If I remember how, I'll let you know.
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Dennis

If it tastes good - it's fattening.

Two of them are obesiting!!

pdfbt40 · Occasional Visitor Joined: Jan 23, 2008 Posts: 56

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