OT:Stupid speed limits ?

[dennis]

I have told you before nobody is a good driver all the time. Some are never a good driver.

The police have killed quite a few while driving too fast in case you didn't know.

[dennis]

OK rod.

[Tim Streater]

Ah, but this is a special tree. It's the one that may or may not make any noise when it falls over in the forest and there's no one there.

[The Natural Philosopher]

Thank f*ck for 'Jane'. Last night in London they seem to have gone 20mph mad...

[NY]

There is the other problem that when a lane is closed (accident, roadworks), the delay that this causes depends on how the traffic merges. If it has plenty of warning and gets over early, it can go through at reasonable speed on the remaining lane(s). If it has no warning of the precise point where the lane is closed, you get two queues of stationary traffic, merging alternately at walking pace. *That* is what causes the worst congestion: when traffic has not merged early into the narrower stream.

I saw this on Saturday. A1(M), between J51 and J50 (a 10-mile stretch) at about 11 AM. It seems that a police car (*) had hit the temporary central reservation in a two-lane roadworks section, and had just been winched out and loaded onto a recovery truck as we got to the lane closure (we overtook the recovery truck just beyond, when traffic was moving freely).

This was preceded by about 9 miles of almost stationary traffic which delayed us by an hour. If only everyone had known to get into a single lane early, we could have gone through at a higher speed. Not the indicated limit of 50, but maybe 30.

The frustrating thing is that when the A1 was upgraded to motorway, they left the old road as a single carriageway for non-motorway traffic. We knew about the roadworks, and my wife has been using the back road to get to work because 60 mph with roundabouts is better than a constant 50 temporary limit on the motorway. On Saturday we decided to risk the A1(M) because we thought it would be quieter at a weekend. Big mistake. If we'd have gone on the parallel A road which runs right alongside, we'd have been at our destination an hour earlier and wondered what had caused the big delays that we could see.

(*) The right hand wing and door had peeled back on impact. It looked a mess. Hope the driver was OK. That will involve a lot of paperwork.

[dennis]

They quite often can't manoeuvrer either as they have lowered the seats too. Then they can't see very well as the steering wheel and bonnet obscure their view. The best thing is a low speed crash which sets off the airbag and its in the wrong place and eliminates the problem.

[dennis]

I hope you are (not) suggesting some household stuff that you must never mix together (and stay there).

[Jethro_uk]

You may be right. You also need to bear in mind ...

- lower speeds leads to lower emissions. Thus sneakily helping the UK government dodge a fine.

- generally the thrust for the past 30 years has been to discourage as much private motoring as possible. Normally by artificially making car journeys longer and more inconvenient. So you have things like f*ck all parking in new builds. Longer pedestrian traffic light phases. Deliberately misphased pedestrain and traffic signals. Lower speed limits. Road width reductions. Making the natural course of a road longer and slower (i.e. the bypass is now slower than the route it bypassed).

So you might be right. But there's been no political will to reduce road congestion. Even now, tens of thousands of cars - a day - will be permanently inconvenienced when the A38 trunk cycleway goes live in SW Birmingham. You'll be able to cycle the 3-4 miles faster than drive it.

[NY]

And the usual policy with ring roads is to build a nice new road and then spoil it by placing roundabouts every half-mile along it, leading to congestion at every one. York's northern ring road is like that: if you want to get part of the way round, it is actually quicker to go the long way round via the dual carriageway and a couple of roundabouts on the single-carriageway northern ring road, than it is to go the shorter route with long queues at each roundabout where the traffic that is travelling radially in/out of town gets tangled up with the traffic going circumferentially around the ring road. Everyone talks about dualling the ring road, but actually the thing that would speed up the traffic flow is converting each roundabout to grade-separated, even without widening the road to dual lane. Sadly it is the grade-sep junctions which cost the serious money; widening one lane to two is less costly. However dualling without removing roundabouts will have bugger-all effect :-(

[charles]

[Snip]

how does that expalain why my car gets best mpg at around 55mph?

[whisky-dave]

I'm not sure why you expect them to be related.

[charles]

If the car consumes fuel it will emit less pollutants.

[dennis]

8<

It may do so, it depends on what gear you have to drive in and is different for each vehicle.

[dennis]

Its lower than 70.

[Jethro_uk]

But *averaged out* over a spread of vehicles and drivers, a 50 mph speed limit (as in effect around most of Brums motorways) leads to less emissions (particulates) than a speed limit of 70.

[Dave Plowman (News)]

Perhaps no one has noticed, but the speed restrictions only come on during very heavy traffic.

The problem being in very heavy traffic, trying to get to 70 mph where possible usually results in some panic stops down the line. With plenty not making them. Lowering the speed limit on a temporary basis in very heavy traffic makes things safer overall. It might on paper cause slightly more congestion - but nothing like a decent accident does.

[whisky-dave]

Although the worst nitrogen oxide(s) are measured in grams per km and not in other terms to do with speed. So I'm not sure how it would be worked out.

It will also use oil and the wheels 'emit' too. but those would be even more difficult to equate with mpg.

[Dave Plowman (News)]

Generally, the lowest speed the car will run at happily in top gear gives the very best MPG too. Be very surprised if that was as high as 55 mph.

Best I ever saw on a previous car - a 3 litre petrol BMW auto - was acting as support car to a Series Land Rover and following it at 40 mph on the M4 very early one Sunday morning. 43 mpg over roughly 100 miles.

[dennis]

It causes less congestion, if people take notice of the limits. The traffic doesn't stall as often so its a constant speed rather than stop start all the time.

Once you get into the stop start traffic flow its hard to get out of it until the traffic volume drops a lot.

The idea of smart motorways is to manage the speed of the traffic to get the highest speed without the stop start.

[The Natural Philosopher]

Oh dear.

Oh dear oh dear.