Road capacity, safety, Infrastructure Bill, DECC spin

Written on a phone waiting for a train, but it’s highly relevant to the discussion at hand.
Roads have a finite capacity. A single lane A-road is notionally 40 mph plus 2 second following distance. In practice the police treat the 40 mph HGV speed limit with the contempt it deserves, and will not prosecute for HGVs at 50 mph on trunk routes. Therefore a single lane A-road is 50 mph plus 2 second following distance. Even without trucks the norm is 50 mph because all it takes is one person not driving at an appropriate speed for the conditions to bring it to a standstill. That one person invariably whinges about “other drivers harassing them” because they’re driving too slowly for the conditions. (Michael)
A double lane road has more than double the capacity of a single land A-road. You drive on the left; you overtake on the right. The double land road can tolerate mixed-mode traffic at 50, 60, and 70 mph (usually 52 cruise for trucks, 62 cruise for coaches and those “doing indicated 70” and 70-75 mph for those “doing indicated 80”) if lane discipline is good. Those people driving in the wrong lane (ie not overtaking the person in the left lane) invariably whinge about “other drivers harassing them” because they’re driving otherwise than in accordance with the highwway code (right lane for overtaking those in the left lane) and without due consideration for other road users (offence). Put your foot down or pull over. (Michael) Many people haven’t read the highway code in so long that they still think the speed limit on a dual carriageway is 60 mph. These are particularly problematic because they’ll sit in the outside lane at an indicated 60 mph with genuinely no clue as to why the line of traffic behind them is so irate.
As a result of appalling lane discipline we cram far fewer cars down a double lane result than the Germans down. UK’s answer? Three lanes. This doesn’t help much because the clueless just treat the inside lane as one for the rucks and sit in the middle/outside lanes. That 3rd (or 4th) lane does very little for capacity.
The initial purpose of “active traffic management” was to make deleting the hard shoulder safe. The idea was that some person would watch the cameras and slow the traffic down if there was an incident, and this made it safe to delete the hard shoulder as a refuge. The research showing that it increases the capacity of the road is awful, and the Highways Agencies own research showed that when they upped the “default speed” for congested times from 50 to 60 mph it improved journey times/increased capacity and didn’t compromise safety on the M42. They’ve done the same thing for what happens when they make the speed limit 70 mph, but daren’t publish the results because it would make the whole thing seem like a catastrophic waste of money.
Meanwhile, on the A14, which really does need a 3rd lane between Huntingdon and Cambridge, they chose to play with speed cameras. The thinking was that 90-60-90-60-90-smack caused problems, and that 70 mph spot cameras (set at 80mph) would fix this. Instead these early fixed cameras had to be torn down because they INCREASED accidents: inattentive drivers who still thought the limit was 60 mph would haul on the brakes at every camera, drop to 50 mph, and cause an accident. They’ve now been replaced with averaging cameras (still set at 80 mph – the police treat the 70 mph limits with the contempt they deserve) and after a number of years even the most retarded of fenlanders have worked out the meaning of the word “average” and stopped emergency braking at every gantry. It works well, and people can just about deal with the concept of two lanes.
This knowledge was fed into the M1 scheme. Normally it is derestricted: no limits displayed AND no cameras active. At peak times it shows an NAL limit and enables cameras set to 80 mph. In very buys periods it drops to 60 mph and sets cameras at 50 mph. Unlike the M42 scheme though, it really does only apply at peak times. You don’t find an empty motorway with limits between 60 and 40 mph because some fat fingered operative decided it was snowing before he fell asleep on the job at 10 pm and left the sign on util 6 am.
Neither of the schemes are actively managed; but the M1 scheme doesn’t pretend that it’s being as clever as the M42 people would like to make out.
With regards “taking pleasure at driving in the outside lane at 60 mph and not being harassed” – this is the wrong attitude. If you’re being harassed it’s because you’re usually driving in the wrong lane. There should be no pleasure in artificially limiting all traffic to 60 mph because the lane discipline of UK drivers is so appalling that a single person in a control room is paying more attention to traffic conditions/their driving than they are.
“Active traffic management” is great if it means increasing the capacity of the roads by having machines drive the cars. If you’re not doing that it’s an enormous waste of time, fuel, and money compared with prohibiting those who can’t drive from using motorways, as the Germans do. For maximising the capacity of roads and minimising journey times there’s nothing quite like actually testing people on their ability to drive on a motorway before issuing a licence, and reinforcing that with the risk of a 155 mph Mercedes S-Class shaped dent in the back of your Ford Ka or Vauxhall Zafira in the event your fail to exercise good lane discipline.
I also get better fuel economy with the cruise set at 70 mph (true road speed) on the derestricted portions of the M42 than is every possible in the 60 mph sections: all the stop-go-stop-go-stop-go muppets who can’t hold a steady speed to save their lives tend to stick in the middle lane on the derestricted parts (for fear of being “harassed” by other road users if they stray into the outside lane) than I do when all these inept people migrate out into the outside lane…

, my own experience matches Michael’s

One key aspect of active traffic management doesn’t appear to have mentioned so far, i.e. it only ‘kicks’ in at times of high traffic volumes.

M1: yes.
M42: no.
Unfortunately one of my trial sites is in Birmingham (I live in Cambridge) which means I have to drive because some fools in a bygone era decided to dig up the westbound train line from Cambridge and replace it with a guided bus for pensioners from Huntindgon to go day-tripping in Cambridge on. I purposefully avoid peak hours yet the “active” managers for the M42 keep screwing up the speed limits.
M1 is better because it’s set on a time clock then ignored. Avoid 08:15 to 09:15 and you’re fine.

Having (successfully) campaigned against the M1 widening back in 2006 (see <http://herbeppel.blogspot.co.uk/2006/11/30-october-2006-eventful-day.html>), I can safely say that the active traffic management that was subsequently introduced on some of the M1 sections, mostly without any actual widening, was certainly a good compromise, compared with the utterly mad alternative of actual widening to build additional lanes!

As somebody who used the M1 to go up and down from Sheffield, I can confirm the active traffic management successfully did nothing at all: a great result.
$150/barrel in 2008 had a far bigger impact.
Roll on £2.50/litre, not allowing anybody to drive on “key routes” unless they’ve demonstrated that they’re competent, and uber/autonomous cars please. No more road building needed.
You’ll need to revoke the old stagecoach union lobbying efforts though, such that it’s legal to offer shared (multidrop) taxi services in the UK using those ubers or autonomous cars.

 

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