Moving house on Saturday I did several trips round the M25 passing through the variable speed limits that are in place between the M3 and M40.
I am not entirely sure how the speed limits are determined, but there were no incidents on the road, just lowered limits of varying rates.
I understand that the theory is that although obviously cars are travelling faster at NSL, due to the effects of braking, distance between vehicles, etc., you can end up getting MORE traffic flowing through at a LOWER speed limit.
However, when driving through, traffic flows well at 60 and somewhat well at 50, and becomes stop-start at 40mph.
It was quite frustrating to be in the 40mph limit, to be stop-start, and suddenly for the traffic to start flowing well, without any junctions in between, only to see the reason for it - that the gantry ahead has gone up to 60mph, causing cars to travel faster.
When you are on the road, it just seems that the Highways Agency are managing things badly, the 40mph speed limits can surely not serve a useful purpose, and they are holding everybody up.
In the case above where the limit went from 40 to 60, this was shortly after the M4 turnoff (going North), so it might be that the traffic flow before the junction was that much greater, and after the turn-off (say two gantries later), improved flow means they can turn the speeds up.
Still, I'm not convinced that 40 can be faster than 50. And are these limits governed automatically?
Does anybody know?
I also think that if these limits really do improve flow, it would make sense to use SPECS cameras, as that would do a better job of keeping speeds steady, and if this ultimately makes people's journeys shorter, it's a good thing (though the problem with this is the ridiculous 10% overstate that are legally permitted on speedometers - my Volvo seems to be perfectly calibrated, but generally most cars are not).
|
I don't think it's the highways agency that are managing things badly, it's the drivers. You're lucky, around here it can become stop-start at 50mph.
I went along a 50mph (roadworks) part of the m/way with average speed cameras a while ago. There are some people who seem to think it doesn't apply to them who pass, but then need to brake. Peoples driving really was shocking, and as a result (I'm guess) the traffic moved very slowly at times, and I couldn't work out why. If people can't drive sensibly at 50mph how do can they expect to be safe at 70+mph?
|
As part of a Geography fieldwork project, when at school, I spoke to Trafford's Borough Traffic Engineer.
He told me the volume of traffic going along a road I was studying. The volume was at its highest when the traffic was crawling slowly (obviously as it tends towards a solid jam then the flow rate reduces again).
|
|
|
