We left home in SELondon/Kent borders today at 2pm, heading 140 miles to the Cotswolds for a week's break. We arrived at 6:20pm. All but 10 miles was motorway and there were no accidents or roadworks on any part of the journey. Gantries were variously at 40/50/60 mph so I can only assume that this was motorway control implementing some sort of traffic management? But at what cost, a lot of very angry motorists arriving very late at their destination. Our journey should have taken 3 hours max Tough if you were heading for Gatwick or Heathrow, bye bye flight

I.ve seen them on the M25 near the M3 which has roadworks (seems like for years) but none on the 25, at 3am with three trucks and a car, posted sign 20mph  Common sense isn't very common.
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2007 Land Rover Freelander2 I6 hse Auto

Sounds much like the M20 between Folkstone and Dover where they put up an experimental 40mph, monitored by average speed cameras. Absolutely frustrating at 5am when it's completely empty. Fortunately most times I used that stretch I was on my Bike and the cameras were facing the front. So V signs all round. MY13 Santorini Black SD4 HSE

Can you imagine what chaos the new runway at Heathrow is going to cause on the M4/M25!?

Why are they planning on using one of the lanes?
They could use the first lane as everybody else seems to use lanes three and four.  Common sense isn't very common.
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2007 Land Rover Freelander2 I6 hse Auto

from time spent at the highways agency telecoms operations centre, I too was surprised at the variable speed restrictions and how they are implemented.

for the majority of time they are controlled by what were called MIDAS loops set into the tarmac (these same loops can be seen in the run up to traffic lights on non M-way routes and are the square lines of tar you see)

They are basically a copper induction loop connected to roadside network equipment that count the frequency and speed of traffic passing over them. The information from these is then used for a variety of purposes, but primarily for automatically adjusting the speed signs on the overheads. The higher the volume and speed of cars passing over them, the lower the speed signs go to control the traffic flow.

However there needs to be a manual override and I feel this is what is sometimes abused by the regional control centres under orders from their higher authority (ultimately the car hating government)

Smart Motorways, only as smart as those that programmed them, or flip the switches Former Mod/Member, with the most post & Chicken George Arch nemesis

Just made the return journey home, marginally quicker at just 4 hours for 140 miles up the M4 then M25. M4 ran ok, it's the bloody M25 where the traffic was controlled all the way round by overhead gantries. First couple of junctions down to 40mph, then next at 60, then next few at 50. Traffic stop, start the whole time, for what reason. No accidents (surprisingly given the traffic flow) no roadworks.
There has to be some justification for it unless as RogB said earlier its some jobsworth obeying a higher authority to press that 'screw everyone up' button. I suppose that the fact there's no accidents, they've justified their actions, but what about those that miss appointments, flights?

They're using this theory that says that slower traffic moves quicker?????  MY13 Santorini Black SD4 HSE

Lived and worked from Slough and Bagshot, within 5 miles of the M25, for 40 years. 35,000 miles/annum for most of that time with the M25 as the main conduit for destinations throughout the UK. Never missed a flight, or appointment. It's just a matter of allowing sufficient time for the conditions--OR--leaving at 5 in the morning. You learn to live with it.

I think common sense would say that we should all plan a journey ahead especially if there's something important at the other end. The point I was trying to make is that all of this 'traffic management' seems way too excessive - it was never like this a few years ago.
As for planning a journey, would anyone reasonably expect to have to take 4:30 hours to cover just 140 motorway miles?

Because I like to play with maths, and because I believe that you can prove anything with statistics providing you can stipulate the starting point of the argument.

Lets say a mile is 5280ft
and a Freelander is 14ft
If from the highway code the breaking distance for 30mph is 75ft, and for 60mph is 240ft - we always have adequate braking distance on the motorway don't we.

so during congestion at 30mph we can fit 5280 / (75+14) = a mile divided by the braking distance and the car length = 59 cars
but at 60mph we can only fit 5280 / (240+14) ) 20 cars

See rolling car park

Based on speed 60mph = 88ft per second
so at 60 mph it would take (254ft / 88ftper second) 2.88seconds for one car to replace the next,
but at 30mph it would only take 89/44 = 2 seconds
So at 60mph average a car passes the camera every 3 seconds, but at 30mph a car passes the camera every 2 seconds - proof to someone controlling the cameras that more traffic flows at 30mph than 60 mph. Tangiers Orange - gone, missing her
Replaced by Ewok what a mistake - now a happy Disco Sport owner

Andy131 - you need to get out more

Agreed with above . . . although I fell asleep halfway through reading it And there was me, the OP thinking it was just down to some arse/jobsworth pressing the gantry on-off signs for a laugh.
Sorry I meant to add, are we assuming the vehicle in the example has a tow-bar, which could affect the overall length and blow those calculations out of the water.

It gets worse if you do the same calcs for 18mph, then you get twice as much as at 30mph - so the optimum speed for the motorway is .................... 18mph

But only if you are operating the camera - not if you are the one trying to get to the airport / work / insert hobby here Tangiers Orange - gone, missing her
Replaced by Ewok what a mistake - now a happy Disco Sport owner