A14 Cambridge to Huntingdon "news"

[KeithW]

So, to get this right. I'm putting down the A1(M) on a nice free flowing D4. But then the inside pops off onto a local road, and it's now D3. It then passes over a junction on what is today the A14 at Brampton hut, which will be still quite busy as there is a service area there and it caters for A14/A1 flows not W/B to NB A1 and S/B to W/B. Then just after this junction dumps it''s SB flows onto the A1(M) we all have to pottle in to lane 1, or squish between some HGV's to tiger tail from lane 2.
Meanwhile heading North. we take the nice new flyover onto the A1 ((m)) and within moment of joining, there is a pull off for A1 N/B flows to the A14 E/B/W/B, local and services.
Right.

Please tell me I'm wrong, and if not how has someone with a nice clean sheet of A4 come up with this?

Edit. Just noticed on one of the links the lane allocations. The A1(M) needs to be D4 between Brampton hut and the A14 EB slip. Mark it as 2+2. Weaving will be bad, but better than the S/B slip joining 1 lane and squishing in between the HGV's, then having to hook over. Gives them a bit more space with D2+2.

Lets look at the actual traffic flows on the existing setup
The traffic flow on the A1(M) before Alconbury southbound is around 70k and as such is FAR from being overloaded

At Alconbury traffic diverges
AADF on the A14 eastbound is around 40 k
AADF on the A1 soutbound is around 30k
The major interchange is A14(M) to A1(M) and is smooth.
The existing D3/D2 A1 southbound is not overloaded In fact once I am south of Alconbury I expect a clear run all the way to Buckden even at peak periods.

At Brampton Hut
While there is some interchange between A1 and A14 its pretty low and uses the roundabout with the A1 on the flyover
The effects on A1 traffic are minimal as the road is freeflow. In 35 years of frequent use of the A1 this is one of the few places I have never been held up.
ALL A14 traffic uses the roundabout - With traffic levels at 40k this is a major bottleneck causing long tailbacks on a daily basis.

Now look at the new setup
At Alconbury the only traffic leaving the A1(M) will be local traffic for Huntingdon and St Ives so the traffic levels on the A1(M) south of Alconbury can be estimated at around 60k - well within the capabilities of a D3(M). As a comparison the D2(M) Doncaster bypass has an AADF of 80k and its still at 70k on the poor quality Redhouse to Darrington D2 section. In fact between Alconbury and Brampton Hut AADF will at about the same level as the D3 A1(M) north of Ferrybridge which flows very freely.

At Brampton Hut
The major traffic flows are all freeflow.

The minor traffic flows , mainly A1 southbound to A14 westbound will continue to be handled by the roundabout but with 90% of the existing traffic gone this should not prove to be a problem.

In an ideal world with an unlimited budget and no consideration being given to maintaining traffic flow during construction perhaps a more elegant solution could have been produced but we do not live in a Sabristic paradise. All civil engineering is the art of the possible, propose a perfect solution regardless of cost and you can expect it to be rejected.

[c2R]

Absolutely, compared with what we could have had, the scheme design is pretty good.

I have always wondered though, why the D4M A1(M) wasn't extended to Fletton Parkway, with a double lane drop there - a great deal of traffic uses this junction at rush hour, (while Norman Cross is relatively quiet) and the exit lane usually has a tailback.

It (and the current A14(M) exit southbound at Alconbury) probably could do with remarking to encourage some traffic from lane 2 to exit, rather than everyone struggling to get into lane 1 for the couple of miles before the exit...

[KeithW]

Absolutely, compared with what we could have had, the scheme design is pretty good.

I have always wondered though, why the D4M A1(M) wasn't extended to Fletton Parkway, with a double lane drop there - a great deal of traffic uses this junction at rush hour, (while Norman Cross is relatively quiet) and the exit lane usually has a tailback.

It (and the current A14(M) exit southbound at Alconbury) probably could do with remarking to encourage some traffic from lane 2 to exit, rather than everyone struggling to get into lane 1 for the couple of miles before the exit...

The same is true at Hook Moor of course and the end result is the same, frequent users tend not to queue in lane 1 but use lane 2 until just before the diverge where there are actually 2 lanes leaving and 3 going straight ahead. I assume they are concerned about excessive weaving in both cases.

[jackal]

Absolutely, compared with what we could have had, the scheme design is pretty good.

I have always wondered though, why the D4M A1(M) wasn't extended to Fletton Parkway, with a double lane drop there - a great deal of traffic uses this junction at rush hour, (while Norman Cross is relatively quiet) and the exit lane usually has a tailback.

At Fletton Parkway the A1(M) doesn't even drop the third lane properly, it's just a regular diverge and then lane 3 disappears at a random point within the junction. I assume this is because they thought the A1(M) would be extended soon after they built the junction. There was a similar arrangement at Dishforth (A1(M)/A168) until the A1(M) was extended.

The freeflow right turn was actually widened to two lanes in recent years as part of the Fletton Parkway widening, so the exit from the A1(M) is even more of a bottleneck. The correct arrangement would probably be for lane 1 to drop, with a tigertail giving the option to exit from lane 2 as well (i.e., layout D1). See discussion here: viewtopic.php?f=1&t=39975

[si404]

Now look at the new setup
At Alconbury the only traffic leaving the A1(M) will be local traffic for Huntingdon and St Ives so the traffic levels on the A1(M) south of Alconbury can be estimated at around 60k - well within the capabilities of a D3(M).

Here's the traffic model from when they were planning the scheme and deciding stuff like number of lanes. It says the 2020 (opening year) with-scheme figure for Brampton Hut-Alconbury is 80500, Brampton-Brampton Hut is 95000, and Bar Hill-Swavesey is 91000 (not including LAR traffic). Now, the actual figure might be 75% of that (ie what you've estimated, which I think is a little low, but reasonably so), but it's not what they were planning on dealing with!

By 2035 (design year) the figures to plan for were 102500, 116000 and 106500 respectively - we're definitely looking at around the threshold where D3M gets put on the "turn me into D4ALR" list here, and new build roads ought not to be designed to be inadequate with the traffic levels they were designed for! The DMRB uses these figures (Annex 5), recorded in 1995, for when certain types of road get congested for more than half their peak hours: D3M 97k, D3AP (trunk) 103k, D3AP (principal) 104k. The reason D3M and trunk D3AP road fair worse is due to the higher proportions of heavy vehicles on them, rather than the cross-section itself (D3M being more capacious than D3AP). That the A1(M) and A14(M) are D3AP cross-sections rather than D3M isn't going to help them here - because they clearly have high levels of heavy vehicles. Obviously there's VSL and other congestion-helping tech that has come about in the intervening 20 years between the DMRB analysis and A14C2H design, but clearly they are playing close to the edge with the design, given the traffic figures they were working with.

Will it be a massive improvement vs before - absolutely! Will it flow well, albeit at a low LOS, for a decade - absolutely! Will the D3 cross-sections cause congestion that needs to be addressed not long after the year that the road was designed for - absolutely!

They'll have done cost benefit analysis on the new parallel section. The proposal is far better than the original which had a 270 degree loop for the main traffic flow!

Indeed - 2020 estimated figures give 56% turning off the A14 onto the A1, 2035 estimated figures give 57% turning off. A TOTSO would have been better (but I can see why they didn't do that), and if they don't plan the paint at the diverge and merge well, there could be issues!

[marconaf]

See detailed plan here with lane allocations and new A14 on old A1 alignment:

https://infrastructure.planninginspecto ... f%2024.pdf

Thanks for that - it confirms the northbound A1 arrives into the new section as D2 and southbound from the new section is also D2.

From weekly driving this bit the overbrige of the A14-A1 link limits this to 2+2 width.

My concern is that this prevents any upgrade of the A1 south to Black Cat or beyond from ever being upgraded to D3, which arguably it needs?

It seems, given the space and new build nature of the alignments it would have been easy to leave room for this to be increased in future?

[KeithW]

Thanks for that - it confirms the northbound A1 arrives into the new section as D2 and southbound from the new section is also D2.

From weekly driving this bit the overbrige of the A14-A1 link limits this to 2+2 width.

My concern is that this prevents any upgrade of the A1 south to Black Cat or beyond from ever being upgraded to D3, which arguably it needs?

It seems, given the space and new build nature of the alignments it would have been easy to leave room for this to be increased in future?

As I understand it the A1 has been widened to 3 lanes between Alconbury and Buckden so I am at loss to understand how this prevents any upgrade to the south from being D3 .

https://www.cambridge-news.co.uk/news/l ... s-16024818

Would you care to explain how this works ?

[marconaf]

Because when I drive up the A1, as I pass over the bridge and hill of the Buckden? Junction with the B1514 (which having been using this route for the past 14 months is generally the southern limit of the road works), I pass under the A14-A1 link road (I think that is the right one) and the A1 is only D2 under that overbridge with what seems to me, no scope for widening.

Now it gains a lane almost straight after that bridge and becomes D3 as the link road from the bridge curves round to merge - but up to that, and under, that bridge it is very much (I think) D2.

Thus the entrance into this section appears to be D2 hence the comments on the limit this imposes on any A1 upgrade south of this.

Now, happy to be corrected if this is an interim solution or if I'm wrong and it could be widened.

Unless of course it will be D3 south of this bridge and it merely drops a lane through the junction - but the B1514 seems unlikely to be worthy of that, and a A1N to A14E seems a very small movement.

google maps is a little unclear due to the aforementioned effective replacemet of the A1 (thanks for clarifying that - despite using it weekly I'd missed that happening!) so the northbound camera actually shows you southbound new A1!

shows southbound, appears like there is space to side of carriageway, but note how narrow the lanes are and that the 40mph limit remains in situ. I think this is a little old and it has more recently (1month back?) been widened out to full width, not least as the section is now full NSL.

shows northbound (but from southbound carriageway, but ironically on the old A1 northbound alignment!)
doesn't look like a D3 width to me - clearly D2 now, no cones or speed restrictions, but the scaffolding around the bridge piers does not indicate to me there is an additional lane width of space.

so - thoughts? again, I'm interested in what has been built, rather perhaps than the HE glossies beforehand

[c2R]

I'm not sure; you might get three lanes through there, without barriers.

Alternatively the thinking might be that if it was upgraded to be wider to the north and south, dependent on turning movements, there would be additional braiding added, effectively in separating car and HGV traffic.... There's examples of this sort of thing in Europe, such as approaching Paris from the south....

I suppose anything's possible - for example look at the strange arrangement where the M6 joins the M6Toll heading northbound from Birmingham....

[KeithW]

Now look at the new setup
At Alconbury the only traffic leaving the A1(M) will be local traffic for Huntingdon and St Ives so the traffic levels on the A1(M) south of Alconbury can be estimated at around 60k - well within the capabilities of a D3(M).

Here's the traffic model from when they were planning the scheme and deciding stuff like number of lanes. It says the 2020 (opening year) with-scheme figure for Brampton Hut-Alconbury is 80500, Brampton-Brampton Hut is 95000, and Bar Hill-Swavesey is 91000 (not including LAR traffic). Now, the actual figure might be 75% of that (ie what you've estimated, which I think is a little low, but reasonably so), but it's not what they were planning on dealing with!

By 2035 (design year) the figures to plan for were 102500, 116000 and 106500 respectively - we're definitely looking at around the threshold where D3M gets put on the "turn me into D4ALR" list here, and new build roads ought not to be designed to be inadequate with the traffic levels they were designed for! The DMRB uses these figures (Annex 5), recorded in 1995, for when certain types of road get congested for more than half their peak hours: D3M 97k, D3AP (trunk) 103k, D3AP (principal) 104k. The reason D3M and trunk D3AP road fair worse is due to the higher proportions of heavy vehicles on them, rather than the cross-section itself (D3M being more capacious than D3AP). That the A1(M) and A14(M) are D3AP cross-sections rather than D3M isn't going to help them here - because they clearly have high levels of heavy vehicles. Obviously there's VSL and other congestion-helping tech that has come about in the intervening 20 years between the DMRB analysis and A14C2H design, but clearly they are playing close to the edge with the design, given the traffic figures they were working with.

Will it be a massive improvement vs before - absolutely! Will it flow well, albeit at a low LOS, for a decade - absolutely! Will the D3 cross-sections cause congestion that needs to be addressed not long after the year that the road was designed for - absolutely!

They'll have done cost benefit analysis on the new parallel section. The proposal is far better than the original which had a 270 degree loop for the main traffic flow!

Indeed - 2020 estimated figures give 56% turning off the A14 onto the A1, 2035 estimated figures give 57% turning off. A TOTSO would have been better (but I can see why they didn't do that), and if they don't plan the paint at the diverge and merge well, there could be issues!

The highest numbers in that document with the new scheme in place are as follows
Table 3: Comparison of 2-way AADT Forecasts on Major Routes in 2035 With
and Without Scheme

A14 Swavesey to Bar Hill - 106.5k
A14 Bar Hill to Girton - 132k
A14 Cambridge Northern Bypass 96k
A428 Near Bourne Airfield 39k
A1198 West of Hilton 19k
A1 North of A14 102.5k
A1 South of A14 72k

This discussion was about the A1 north of the A14 which will be D3M. I seem to recall that the DMRB calls for sizing to be done on the basis of of the opening year and for the A1 north of the A14 the applicable figure is 80.5k, As you say it MAY be necessary to think in terms of ALR for the new section of A1(M) by 2030 or so but should that come to pass the new D3(M) section will be the least of the problems. Lots of luck getting 72k through Buckden , the Kelpie Marine boatyard curve and Sandy or 96k along the Cambridge Northern Bypass !

Realistically within the scope of this scheme the most that could be accomplished is to design in the capability to increase the capacity of the new roads being built should that need to happen. Had HE put forward a scheme to build the new A14(M) and new A1(M) as D4 (M) from the start I suspect that would have been dismissed outright. Civil engineering and indeed all engineering is about doing the best you can with the resources available. Personally I think HE have done remarkably well in the case of this scheme.

[si404]

This discussion was about the A1 north of the A14 which will be D3M.

I don't see any hard shoulders in the current plans (and they were expressly and explicitly ruled out very early on in the process). Are they there on the ground? If so, great! If not, the cross-section is D3AP, regardless of the colour of signs or legal status of the road.

I seem to recall that the DMRB calls for sizing to be done on the basis of of the opening year and for the A1 north of the A14 the applicable figure is 80.5k

Yes - the part of the DMRB I linked to in my earlier post has it. They clearly didn't follow the recommendations in Table 2.1. I didn't discuss it as these are more economic/political guideline figures than physical ones like the congestion ones.

Let's take the 80.5k figure for Brampton Hut-Alconbury, the least busy of the three potentially problematic new D3AP sections, with the other two problem ones going beyond the maximum opening year traffic level where D4M is recommended (Brampton-Brampton Hut at 95k, Bar Hill-Swavansey 91k):
D3AP is recommended for opening year figures of 23k-54k
D3M is recommended for opening year figures of 25k-67k
D4M is recommended for opening year figures of 52k-90k

So it has 149% of the recommended maximum opening year traffic on it. Now, mid-90s politics/economics (cf Alconbury-Peterborough) are rather generous with new-build road capacity, but 149% of the recommended maximum (178% on the bit to the south!) clearly fits my point - that the design is playing close to the edge of being inadequate.

Realistically within the scope of this scheme the most that could be accomplished is to design in the capability to increase the capacity of the new roads being built should that need to happen.

I totally agree - political considerations made it impossible to not have a road that was designed for a design year where the traffic models suggest that the road will be congested enough to at least be considering widening it (obviously congestion issues will exist elsewhere on the SRN in the area come 2035, like the 1950s A1 and the 1980s Cambridge Northern Bypass, unless they have be widened. But they are far older roads, rather than in their design year!).

However, has this road been designed with upgrade capability in mind? It seems like it hasn't. Which, when you design a road to be right on the cusp of being congested enough to warrant widening within 20 years...

[thatapanydude]

Whilst you can maybe understand in this current climate why the A1 has been built to a D3 standard with no HS, I believe building these new bridges with no upgradability to D3(HS) and D4(HS) north of Brampton, is an unforgivable mistake.

Sticking a HS and a extra lane of the A1 for only 3 miles or so, would not have costed the earth. Additionally there would have been no need for variable speed limits and the associated costs with the technology and gantries.

I am also disappointed about the short-sighted nature of the scheme with no bypass of Buckden. Likewise with the Black-Cat upgrade further south on the A1 where the new slip roads for the 3 level stack are being plugged into the Tempsford 90 degree bends.

Anyway as I have suspected for a few years now, I don't believe the A1 will be upgraded to a Motorway and the best we can hope for are just bypasses for Buckden and Sandy.

[Johnathan404]

Sticking a HS and a extra lane of the A1 for only 3 miles or so, would not have costed the earth. Additionally there would have been no need for variable speed limits and the associated costs with the technology and gantries.

Regardless of whether you agree or not, the fact is Highways England feel hard shoulders are a negative and will not be provided on any new road, all-purpose or motorway. Likewise they believe that smart technology is a must that any major new road needs.

So it's pretty easy to understand that no provision for a hard shoulder has been made because Highways England effectively don't believe that there is any such thing as a hard shoulder any more.

[Herned]

Whilst you can maybe understand in this current climate why the A1 has been built to a D3 standard with no HS, I believe building these new bridges with no upgradability to D3(HS) and D4(HS) north of Brampton, is an unforgivable mistake.

Sticking a HS and a extra lane of the A1 for only 3 miles or so, would not have costed the earth. Additionally there would have been no need for variable speed limits and the associated costs with the technology and gantries.

I am also disappointed about the short-sighted nature of the scheme with no bypass of Buckden. Likewise with the Black-Cat upgrade further south on the A1 where the new slip roads for the 3 level stack are being plugged into the Tempsford 90 degree bends.

Anyway as I have suspected for a few years now, I don't believe the A1 will be upgraded to a Motorway and the best we can hope for are just bypasses for Buckden and Sandy.

Given that the government wanted it tolled at first, and had seriously cold feet, I think the scheme being built is as good as could be expected. Yes, ideally it would have all been built with some future proofing, and the bridge at the southern end of the A1 segment does seem particularly short-sighted, but at least something on a decent scale has been done

[Al__S]

Whilst you can maybe understand in this current climate why the A1 has been built to a D3 standard with no HS, I believe building these new bridges with no upgradability to D3(HS) and D4(HS) north of Brampton, is an unforgivable mistake.

Sticking a HS and a extra lane of the A1 for only 3 miles or so, would not have costed the earth. Additionally there would have been no need for variable speed limits and the associated costs with the technology and gantries.

I am also disappointed about the short-sighted nature of the scheme with no bypass of Buckden. Likewise with the Black-Cat upgrade further south on the A1 where the new slip roads for the 3 level stack are being plugged into the Tempsford 90 degree bends.

Anyway as I have suspected for a few years now, I don't believe the A1 will be upgraded to a Motorway and the best we can hope for are just bypasses for Buckden and Sandy.

it's as if the A14 scheme is about the A14 and the A428 scheme is about the A428, and they're minimising how far beyond the scope they go. Fixing Buckden and Tempsford are outside of the objectives of each scheme

[marconaf]

So pax took this today southbound at the join of the new A1 to old A1, ie where any future A1 upgrade bypassing buckden and black cat would extend from.

Now full width and NSL, no chance of D3.

I disagree the new A1 buts need more lanes on this section generally - but the lack of future proofing in bridge width especially at the southern joins to the old A1, given the near total freedom to build them in the area and that a wider one would cost basically exactly the same - is sheer wanton stupidity.

I think any offline A1M upgrade is dead, unless some crazy thing that also bypasses this A1-A14 section, perhaps fly over the entire lot and take the current A14 spur to join the existing A1M, with A14 traffic coming off at Black Cat and using the old road to get there! Afterall - is A1N to A14 a big movement? I thought most of the congestion was the hiatus the roundabout gave to through A14, and A14 to A1 North traffic?

[c2R]

So pax took this today southbound at the join of the new A1 to old A1, ie where any future A1 upgrade bypassing buckden and black cat would extend from.

628A7DF9-B631-4490-820A-1B2DBB72A84A.jpeg

Now full width and NSL, no chance of D3.

I disagree the new A1 buts need more lanes on this section generally - but the lack of future proofing in bridge width especially at the southern joins to the old A1, given the near total freedom to build them in the area and that a wider one would cost basically exactly the same - is sheer wanton stupidity.

I think any offline A1M upgrade is dead, unless some crazy thing that also bypasses this A1-A14 section, perhaps fly over the entire lot and take the current A14 spur to join the existing A1M, with A14 traffic coming off at Black Cat and using the old road to get there! Afterall - is A1N to A14 a big movement? I thought most of the congestion was the hiatus the roundabout gave to through A14, and A14 to A1 North traffic?

As I said above, additional braiding could be introduced, particularly if a new A1 bypassed the existing offline.

[marconaf]

sorry for being thick - but do you mean braiding as in a lane drop through the bridge? I'm just not sure how braiding (which I think of as lots of white paint on the road in stripes) helps a potential D3 plug into a D2 bridge.

Of course all this assumes an A1 upgrade online or offline from say the Hatfield A1(M) to the new A1(M) is actually D3, and not just a case of D2 but with the Black Cat and roundabouts north of that GSJd to freeflow. Which to be fair might just be enough, especially if the Oxford Cambridge route, and upgraded A14M take flows instead.

After all a large and dense network of D2s may be far better than a few trunk D3/4 and a mass of S2s which is more akin to what we have now - point to point concept rather than hub/spoke of big motorways? With the talk of towns getting ring roads and a big expansion of expressways to properly complete D2 routes, is this perhaps where things are going?

[c2R]

sorry for being thick - but do you mean braiding as in a lane drop through the bridge? I'm just not sure how braiding (which I think of as lots of white paint on the road in stripes) helps a potential D3 plug into a D2 bridge.

Sorry, my fault for not expanding... it's essentially the use of parallel carriageways to avoid weaving or conflicting traffic - the simplest example would be here, where the M1 joins the M25 after the A405 has left

https://www.sabre-roads.org.uk/maps/ind ... 15&layer=0

The most complex example we have in the UK is at Worsley: https://www.sabre-roads.org.uk/maps/ind ... 4,-2.36916,



However, this is where you would take the example to the extreme, in France, where slower vehicles are separated from main line, and merged with slower vehicles from otherroad while cars merge with cars - this requires additional bridges but works well: https://www.sabre-roads.org.uk/maps/ind ... 4,-2.36916,

[jackal]

So pax took this today southbound at the join of the new A1 to old A1, ie where any future A1 upgrade bypassing buckden and black cat would extend from.

628A7DF9-B631-4490-820A-1B2DBB72A84A.jpeg

Now full width and NSL, no chance of D3.

You can see that there is plenty of space on either side in front of the barriers, and more space still if the barriers were removed and the replacements flush to the supports. It could be a quirk of the camera angle, but the lanes also look like they may be a little beyond standard width. At any rate there is certainly space for 3 lanes. The question is how wide the lanes could be and if NSL would still be possible.