M62 Manchester to leeds

Mr_Toad

!!!!!! wrote: »

Surely only if the limit is increasing as you go along?

From what I saw many moons ago on the M42 instead of a constant stream of traffic you ended up with bunches. I suppose it allows those coming on to the motorway to join in a relatively traffic free area.

And don't talk to me about using the hard shoulder as a 4th lane that suddenly turns into a lane only for the next junction.

No. What happens is traffic ahead of you starts to bunch and while the front of the bunch rarely comes to a stop the traffic behind catches up and the further back the slower it gets until it comes to a stop.

When bunching starts the speed is reduced way back to slow traffic which allows the bunched traffic to pick up.

A lot of people think that there's some bloke in room somewhere setting the variable limits, there isn't they are set by computers monitoring the traffic ahead, if it slows they slow you too.

harrys_dad

Traffic flow is actually a very complicated mathematical exercise to model accurately. How many times have you been in near stationary traffic and then got to the front to find no blockage? Something as simple as a vehicle doing 50mph in the inside lane on a busy motorway can cause stationary traffic 5 miles further back behind it.

The managed motorway sections have their speed limits calculated using complex modelling based on traffic sensors and they do work. I was a regular traveller on the M42 for years before they introduced managed motorways and they are brilliant. Most, but not all, of the jams at busy times disappeared. Much better to drive at a constant 50 that half at 70 and half at 10.

Richard53

I'm not a big fan of automated speed enforcement generally, but I like the variable limits/managed motorways. My job used to take me regularly on the M25 between the M4 and M23, and the jams could be horrendous. After the variable limits were installed, it was a much nicer journey. People generally stuck to the signs, so you had three lanes doing 60 or 50 or even 40, but flowing freely. A constant speed, even if it is modest, is far better for the car and driver than stopping and starting.