A1(M) Junction 6 to Junction 8 Smart Motorway

[thatapanydude]

To be fair the southbound A1 does lose a third of its traffic to the A14 at Brampton so it's somewhat logical that that's where the quality drops off.

I personally think J6-8 is a higher priority as it's far busier and a glaring D2 bottleneck between D3 sections. Baldock to Brampton is a vastly more expensive long term aspiration that shouldn't be an excuse to hold up more deliverable schemes.

I disagree with that assessment - firstly J6-8 is only really busy when it fills up with commuter traffic centred around Welwyn, Hatfield, Letchworth, Baldock, and Stevenage - for the most the day, there is not a significant issue - this can be seen by the fact that the D2M section south of Hatfield copes fine. I would argue that increasing capacity on this section will only release currently suppressed demand. Have we also got an answer yet as to the level of structure and hard shoulder reconstruction that is required for 6-8? It's a fairly old section of motorway, and so I don't think that it's going to be as straightforward as putting in a couple of ERAs, a concrete barrier, and getting out the white paint...

The section between Brampton and the Black Cat on the otherhand has a number of at grade junctions, poor alignments, and contributes to significant local severence in the villages mentioned above. While it is less busy clearly than the D4M section between Alconbury and Peterborough, there is still a large amount of strategic traffic heading to/from distribution centres at Milton Keynes, and also using the A1/A421/M1 to route towards London. I would therefore argue that Brampton to the Black Cat is more urgent.

Apologises on digressing a bit but I would add that "Brampton to Black Cat" would not be that expensive too. As the Wyboston section is being tided up as part of the A421/8 Black Cat scheme so it only needs straightening up at Southoe and a Buckden bypass - though I my opinion the A14 scheme was a missed opportunity for that with the new tie-in on the A1 leaving a very tight turn to bypass Buckden on the west. Still any scheme ought to be competitive with any smart motorway scheme further south - I agree too that it will almost certainly push traffic issues northwards to the inadequate A505 junction and southwards onto the already overcapacity A414 not-forgetting exacerbating the rush-hour queues at South Mimms and Borehamwood.

My wish would have been at least extending the D3(M) to the end of a new Buckden bypass as part of the A1(M) though any scheme now will we almost certainly all-purpose.

[jackal]

The section between Brampton and the Black Cat on the otherhand has a number of at grade junctions, poor alignments, and contributes to significant local severence in the villages mentioned above.

Obviously I agree it would be great to get it upgraded. The question is where do you find ~£1bn from the RIS budget to do that? Cutting J6-8 isn't anything like enough - you'd need to cut 5-10 schemes of that size. There's the rub.

While it is less busy clearly than the D4M section between Alconbury and Peterborough

As an aside I might mention that, unlike Brampton to Black Cat, A1(M) J6-8 is not less busy than north of Alconbury - it carries the same traffic on half the lanes. Hence why ALR is such a no brainer.

[c2R]

The section between Brampton and the Black Cat on the otherhand has a number of at grade junctions, poor alignments, and contributes to significant local severence in the villages mentioned above.

Obviously I agree it would be great to get it upgraded. The question is where do you find ~£1bn from the RIS budget to do that? Cutting J6-8 isn't anything like enough - you'd need to cut 5-10 schemes of that size. Which ones?

While it is less busy clearly than the D4M section between Alconbury and Peterborough

As an aside I might mention that, unlike Brampton to Black Cat, A1(M) J6-8 is not less busy than north of Alconbury - it carries the same traffic on half the lanes. Hence why ALR is such a no brainer.

Yes, I'm aware of that - however, the majority of that is during the rush hour gridlock caused by the commuter traffic I mention above... I used to live in a village directly affected by people finding alternative routes around that - which is why I'm also pretty sure that the amount of suppressed demand is so large that providing an additional lane of capacity will just fill up immediately. If we're trying to predict and provide for commuter traffic here, we'd be looking at least at D4M, with potentially collector distributor lanes between some of the junctions...

[jackal]

Relieving villages of rat runners and putting them on motorways instead doesn't sound so bad to me...

[trickstat]

Relieving villages of rat runners and putting them on motorways instead doesn't sound so bad to me...

For a short period after I started driving (in 1987) I used to commute between Stevenage and Hendon and, coming home, I would sometimes turn off at J6 and go through Knebworth.

Since moving to Letchworth, on the rare occasions when I've been heading northbound during the evening peak, I have occasionally turned off at J6 and headed home via the B656 and various country roads.

Usually (i.e. not this year), there are a couple of times a year when I need to be in SE Stevenage at about 8:30 AM. I will always leave enough time to take the B197 and a circuitous route around the north and east of the town rather than risk the lottery of the A1(M).

[Bryn666]

Relieving villages of rat runners and putting them on motorways instead doesn't sound so bad to me...

Only it doesn't. The M65 reduced traffic on the B-road outside my parents old house for a few years but now it's busier than it was before the motorway was built because some genius decided all that new motorway capacity had to be filled by building industrial estates and box sheds along it, thus completely obliterating the function of the M65 as a bypass. J4-5 is the busiest section and it's because everyone is transiting between two massive distribution parks.

Designed for 38,000 AADT by 2010, it carried 51,000.

This has been explained numerous times before that you have to provide measures to prevent induced demand from new roads but planners keep looking at spreadsheets and whinging that mitigation is too expensive so these villages are actually sacrificed at the altar of BCR and swallowed up by shed development spurred on by that massive new road that apparently has to 'service the economy' instead of 'service quality of life' because WebTAG has no method of calculating quality of life but it can quantify all the other crap that unmitigated road building generates as a 'win'.

[thatapanydude]

Just been looking at the AADF here and while 7-8 is at 75k, 6-7 is well up on 2018 and 2017 at 95k!

This along with the A406 2-lane sections nr Walthamstow must be the highest D2 roads.

[Micro The Maniac]

This has been explained numerous times before that you have to provide measures to prevent induced demand from new roads

By induced demand, I assume you include the previously suppressed demand? ie the traffic that would have used the official route but don't because it is too congested?

[jackal]

Just been looking at the AADF here and while 7-8 is at 75k, 6-7 is well up on 2018 and 2017 at 95k!

This along with the A406 2-lane sections nr Walthamstow must be the highest D2 roads.

A406 through the M11 junction is the highest D2 I've seen (103,997 a few years back). Some discussion: viewtopic.php?f=1&t=41782

That J6-7 number is really extreme though. Some D3Ms have been converted to D4 around that level. Bizarre that even the D3 ALR has dropped out of the programme.

[Chris Bertram]

This has been explained numerous times before that you have to provide measures to prevent induced demand from new roads

By induced demand, I assume you include the previously suppressed demand? ie the traffic that would have used the official route but don't because it is too congested?

Suppression of demand seems to be the name of the game in some traffic planning circles.

[marconaf]

This has been explained numerous times before that you have to provide measures to prevent induced demand from new roads

By induced demand, I assume you include the previously suppressed demand? ie the traffic that would have used the official route but don't because it is too congested?

Suppression of demand seems to be the name of the game in some traffic planning circles.

The railway only works at all because fares do exactly that. In BR days it was the standard management procedure. It feels like we are seeing a reversal over the decades for different modes (witness HS2) although personally I prefer “predict and provide” to be applied uniformly and then rely on the inherant advantages/disadvantages of different modes to drive usage - rather than have people decide other peoples desires are less worthy than their own and seek to suppress them, or complain when something is built and finally people can advance/ease their life and label it “induced” as if they are just using it out of spite or something.

[jackal]

Not sure how long it has been up, but the environmental assessment report (dated June 2019) is available on the scheme page. It describes it as follows:

The Proposed Scheme would provide three permanent running lanes, by converting the hard
shoulder into a running lane (lane1), between junction 6 and 8. Through junction running will be
provided at junction 6 (northbound only) and junctions 7 and 8.

So combined with existing sections (and considering that J6 already has three lanes southbound) there would be three lanes all the way from J3-J9

The scheme has of course been delayed to RIS3 (speculated to be because the Secretary of State could do without smart motorway controversy in his own constituency).

https://s3.eu-west-2.amazonaws.com/asse ... ll+EIR.pdf

[KeithW]

There is a massive difference between Victorian engineering, where the engineer was king and the aim was to deliver the best possible railway. Against an early 60's motorway where the accountant was king and the political masters were interested in short term targets ( such as 1000 Miles of new motorway in 5 years ).

At least the A1(M) does have continuous hard shoulders unlike the M50 from the same era.

The Victorian era had more than its share of short lived bridges. Many of the structures on the GWR built by Brunel were built with timber. They had to start replacing them from the 1870's onwards.
http://www.engineering-timelines.com/wh ... cts_03.asp

A significant number of minor lines were marginal as built. A classic example was the Whitby, Redcar and Middlesbrough Union Railway which was built to a tight budget and by the 1950's many of the structures were so unsound there were speed limits on all of them and they were closed if the windspeed exceeded 30 mph. At last one viaduct was so unstable it had to be infilled turning it into an embankment.

See this example

[JohnnyMo]

Just been looking at the AADF here and while 7-8 is at 75k, 6-7 is well up on 2018 and 2017 at 95k!

This along with the A406 2-lane sections nr Walthamstow must be the highest D2 roads.

A406 through the M11 junction is the highest D2 I've seen (103,997 a few years back). Some discussion: viewtopic.php?f=1&t=41782

That J6-7 number is really extreme though. Some D3Ms have been converted to D4 around that level. Bizarre that even the D3 ALR has dropped out of the programme.

Especially given the gradients of that section, in both direction. When I've used that in the rush hour I feel the gradients rather than traffic flow is the problem. One HGV struggling to accelerate can cause a massive problem.

[c2R]

It's more than the gradients - in the morning, the southbound traffic entering the A1 at Langley Sidings causes a significant interruption in the flow, as there's so much traffic from Stevenage wanting to head south, joining Stevenage bypass traffic that's already approaching capacity. Uncontrolled building of cheaper housing in South Bedfordshire has resulted in people moving further north while still working in the A1 corridor.

Northbound, the gradient is a definite factor at the Clock, and various different arrangements have been trialled with regards to when to drop the lane, but essentially here you've got a gradient, and a lane drop, and a local access to the motorway (which is also used by people trying to get ahead of the queue at the junction.

Finally, there's a significant amount of suppressed demand, with traffic heading through local towns and villages to avoid the section. I think that D3ALR will quickly become as congested as the current D2M arrangement; although hopefully to the benefit of people living in the communities in the area that are currently used to rat-running.

[JohnnyMo]

It's more than the gradients - in the morning, the southbound traffic entering the A1 at Langley Sidings causes a significant interruption in the flow, ...

Given that, in most other cases a quarter of a mile past the junction, traffic begins to flow freely again. In the case of Stevenage south this does not happen until the brow of the hill.

I do admit northbound is worse as traffic is starting on the incline.

[JRN]

Have to say I was hoping this would be cancelled and replaced with a conventional widening scheme.
Not generally against smart motorways (as a short term, stopgap solution until we realise the necessity of real road building) but think this might be a poor fit.
It's introducing a short section of smart motorway on a longer stretch of road, other sections of which are unlikely to become smart motorway.
I'm not sure about using ALR to widen D2M to D3ALR. I know that ALR motorways have somewhat narrower lanes than normal motorways, due to the narrower width of the hard shoulder, the difference being then spread across the resulting lanes.
But with only 3 lanes, the percentage difference would be larger - will this scheme end up with narrower lanes than a D4ALR?

[jackal]

Have to say I was hoping this would be cancelled and replaced with a conventional widening scheme.
Not generally against smart motorways (as a short term, stopgap solution until we realise the necessity of real road building) but think this might be a poor fit.
It's introducing a short section of smart motorway on a longer stretch of road, other sections of which are unlikely to become smart motorway.
I'm not sure about using ALR to widen D2M to D3ALR. I know that ALR motorways have somewhat narrower lanes than normal motorways, due to the narrower width of the hard shoulder, the difference being then spread across the resulting lanes.
But with only 3 lanes, the percentage difference would be larger - will this scheme end up with narrower lanes than a D4ALR?

I don't know that it's true that ALR motorways have narrower lanes than conventionally widened ones. Certainly widening schemes often narrowed the lanes. For instance the M25 J16-23 widening "involve[d] reduced lane widths at 26 locations where Secretary of State owned land was constrained or the carriageway passed an existing structure" (POPE OYA). Lane widths at the Chalfont viaduct are a pokey 3.6, 3.5, 3.3, 3.2m.

By contrast, the lane widths for the J6-8 scheme were given as 3.65, 3.5, 3.4m, which is not really so bad (see link in my previous post).

[JRN]

Have to say I was hoping this would be cancelled and replaced with a conventional widening scheme.
Not generally against smart motorways (as a short term, stopgap solution until we realise the necessity of real road building) but think this might be a poor fit.
It's introducing a short section of smart motorway on a longer stretch of road, other sections of which are unlikely to become smart motorway.
I'm not sure about using ALR to widen D2M to D3ALR. I know that ALR motorways have somewhat narrower lanes than normal motorways, due to the narrower width of the hard shoulder, the difference being then spread across the resulting lanes.
But with only 3 lanes, the percentage difference would be larger - will this scheme end up with narrower lanes than a D4ALR?

I don't know that it's true that ALR motorways have narrower lanes than conventionally widened ones. Certainly widening schemes often narrowed the lanes. For instance the M25 J16-23 widening "involve[d] reduced lane widths at 26 locations where Secretary of State owned land was constrained or the carriageway passed an existing structure" (POPE OYA). Lane widths at the Chalfont viaduct are a pokey 3.6, 3.5, 3.3, 3.2m.

By contrast, the lane widths for the J6-8 scheme were given as 3.65, 3.5, 3.4m, which is not really so bad (see link in my previous post).

Huh. Those lane widths for the A1(M) scheme actually sound OK. The outside lane is not as narrow as on D4ALR..?

Re the M25 widening scheme, to be fair, under the viaduct is an exceptional lane squeeze. I know it would have cost extra but I given the proximity to J16 I wish they would have lengthened the sliproads (requiring some land take, an overbridge replacement and 2x new underbridges) and put them through the adjacent arches, then had the merge to the north.

[M4Simon]

Re the M25 widening scheme, to be fair, under the viaduct is an exceptional lane squeeze. I know it would have cost extra but I given the proximity to J16 I wish they would have lengthened the sliproads (requiring some land take, an overbridge replacement and 2x new underbridges) and put them through the adjacent arches, then had the merge to the north.

I think you've just stated the reasons why this was not done.

I drive under viaduct reasonably frequently, often in lane 3 or 4, and I've never felt that the lane is too narrow. In cost-benefit terms, I doubt the extended slip roads would stack up.

Simon