The future of smart motorways

[Darren]

And yet on the ALR sections where extra ERAs are being installed, a lane is taken out for the duration of the construction period. In the case of the M1 in South Yorkshire, that's around 18 months, up to "Winter 2024". Might one suggest that for that length of time one might have been able to construct a hard shoulder or two?

Yes, that'd have been a great idea - but the snag is the land take required means it's a non-starter. Certainly the projects nearest me (including the M20) were constrained by land take - acquiring extra land for a hard shoulder would have been a PITA in term of planning, and payments, so they took the cheap, fast and easy option. Of course we now get to "enjoy" going back to 3 lanes with a bonus 50mph speed limit for a year or more, which is just great.

This country is simply incapable of doing anything major in terms of infrastructure in a timely fashion, it seems. Just look at how much fuss has been made over building a railway line (now cancelled), an extra runway at an airport (decades of arguing and still no closer) or even a tunnel under the Thames (hundreds of thousands of pages of planning and still a long way from works starting). The period of the 60s to the 90s now looks like a golden era in comparison, perhaps just squeezing into the early 2000s with the M2 upgrade.

I'm really dreading my regular journeys to Reading now (from Sheppey in Kent). It looks like the M4 and M3, as well as chunks of the M25 and M20 are all going to be coned down to three lanes with a 50 limit at the same time, which will be pretty dreary to deal with. At least when the smartification was underway it was generally only one motorway being done at a time!

[DB617]

Fair point - I dread to think what a lot of major projects like the Medway Viaduct, the M5 across the Severn levels, the M4 Second Severn Crossing and many more would have looked like under today's planning and delivery conditions. This country would be in big trouble if we were only now thinking of building these critical bits of infrastructure.

[nowster]

ALR failure - it's just a normal D4, i.e., fails safe by any normal measure.

There's no such thing as a normal D4.

Not sure what you mean by that - there are plenty of stretches of non-ALR/DHS D4... the M1 and M25 being two obvious motorways - in fact the M25 had D5 and even D6 on its western stretch.

But they're D4M formation (ie. with shoulders). M60 through the Irwell ("death") valley is D4M from the 1990s. The stretch between Oldham and Ashton-under-Lyne was built as D4M.

In fact some of the original D4M stretches had shoulders on either side of the running lanes.

D4 on non-motorways with 70mph limits was incredibly rare.

[nowster]

I won't go through the whole argument again here, but, briefly, left-most lanes operate in an inefficient 'lane-changing' state because they're influenced by exits and entrances, whereas right-most lanes are insulated and flow un-interruptedly.

Until you get the lane 3 hogger with no situational awareness at 50mph.

[Conekicker]

An important difference is that (other than in some very low-speed situations) trains are driving to the signals, not on sight, whereas road vehicles are supposed to be driven on sight. A train driver seeing a green signal means they can proceed at the maximum allowable speed, even if they can't see far ahead. A driver on a road vehicle should never assume that any sign means they don't have to look at the road and respond to what's in it. If a driver enters an unsafe situation blindly that's entirely on them, whatever signs say. If a railway signal were to do that with a train it wouldn't be the fault of the driver.

Supposed to be, certainly. In which case there's no problem with there being a stopped vehicle in a live lane, and ALR is perfectly safe with no "smart" needed - drivers will see the stopped vehicle and stop before hitting it. In practice that isn't the case - so motorway traffic is clearly not driving completely "on sight" in practice. Which is why my suggestion was that, in case of failure of the "smart" systems, the speed limit should default to 40mph - at that speed, there's much more chance that drivers really can stop short of an unexpected obstruction.

On a normal D3 with hard shoulder there should be nearly always the full 295M SSD (120kph/70mph). HSR sections I am aware of varies, as a minimum, between 160m (80kph/50mph) and 215m (100kph/60mph) SSD. With ALR there are many relaxations on SSD in LBS1 (and occasionally LBS2).

M42 ATM etc was designed to be safe with everything off. This is not 'partially working'. Given the reliably of the technology, going all the way back to 2002, did not allow for 24/7 use, there was never the chance that the system could put out a default 40mph, nor drivers assume a 40 mph limit if every thing was off. In 2005 MTBY for a AMI in use up to 18 hours a day was supposed to be 5 years; on 24/7 it was calculated to be barely 6 months.

It has to be remembered that ATM/MM/SM were never safety schemes. Also ALR was driven by the technology specialists and not highway safety standards specialists. Without being smug, they were told.

Ah yes, the "told" ones.

We'll carefully skip over the hard fought battles there were to get the ROTTMS to have battery back-up and not have to rely on just mains power - like the permanent signalling does. Because, according to certain people, the mains power wouldn't fail. Nor the attitude of some that the batteries could be removed after a few years.

I've no idea what the current position on them is of course.

[tom1977]

As usual, National Highways make it hard to find anything on their website, but here is their official response to the Panorama programme

https://nationalhighways.co.uk/article/ ... echnology/