Gatwick Airport's Highway improvements (A23/M23/A217)

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jervi
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Gatwick Airport's Highway improvements (A23/M23/A217)

Post by jervi »

So today Gatwick Airport Limited (GAL) opened their first public consultation for large works to be carried out on the airport to increase passenger throughput to 75m from 64m.
Overall the changes involve moving and reconfiguring the current Northern runway (the emergency runway) to be 12m further north to allow for dual runway operations. There is also proposed to be a new pier, extensions to existing terminals, new hotels, new car parking etc.
However there are also plans for the road network which I am most interested in.

M23 Spur - More widening!
They appear to want to make the Eastbound carriageway of the spur to 3 lanes. As part of the SMP last year the Spur was widened to 3 lanes westbound with no hard shoulder and a fixed 50mph while the eastbound remained as a 2 lane with hard shoulder. Plus the medium barrier was replaced with concreate. It is proposed that eastbound to become a D3ALR as well, although I'd suspect a fixed limit of 50mph rather than VSL or NLS. No proposed changes at M23 J9

Airport Way Roundabout East (M23 J9a) - Grade Separation!
It is proposed that the current at-grade 3 lane roundabout will be replaced with a standard roundabout interchange. Operating as a lane drop/gain as the M23/A23 heads over the junction. Due to the slip roads, this will also require works at the B2036 Balcombe Road Bridge. Also the merge/diverges don't seem like the best option to me. The airport access road will also be widened to D3 from D2, although that might just for illustration purposes.
M23J9a-min.PNG
Airport Way Roundabout West - Current Limited Access confusing layout is becoming a full access even more confusing layout.
The map is a little hard to follow since its not showing carriageways remaining the same, so free flow A23 SB to Airport Way (A23/M23 Spur) is remaining.
The current Roundabout is being completely removed, with two sets of traffic signals & a new fly over (Airport Way to A23 NB) replacing it. The proposed layout does allow for more movements than before, as well as providing better access to the local road network onwards to both Horley and Crawley to avoid longer routes.

Longbridge Roundabout
Some minor changes are proposed at Longbridge Roundabout (A217), although these are very minor and just involve inadequate NMU provision.
It does appear that a signalised crossroads was considered, although I think a roundabout is better as it allows u-turns
Longbridge-min.PNG
Video of highway improvements: https://player.vimeo.com/video/599699161?h=6ec4f33eff

Unfortunately, at this stage they have not said anything about improving cycle and pedestrians routes, other than the minor adjustments at Long Bridge Roundabout. The consultation documents say they provide 300 bicycle parking spaces and are going to increase that and provision of lockers and shower rooms for staff. They also say "We are also proposing to enhance footpaths and cycle paths", although nothing specific has been mentioned.

These works are likely to take place 4-8 years into the project, which is going to start in 2024 at earliest. So we are looking at these changes happening around 10 years time, but still nethertheless.

From the SABRE Wiki: Gatwick Airport :

Gatwick Airport is the world's busiest single runway airport. It was also the first airport in the world to have a rail link with the first Gatwick Airport opening in 1935. After the Airport was taken over by the Government during World War 2, it reopened and the airport was rebuilt in 1958 with the railway station built at the current location, at the same time the A23 was diverted around its Eastern and Southern sides as a trunk dual carriageway. In 1976, the M23 opened along

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Re: Gatwick Airport's Highway improvements (A23/M23/A217)

Post by jackal »

Thanks for sharing this.

Some of the north terminal changes are a bit clearer from the video:

Gatwick existing - Copy.jpg
Gatwick proposed - Copy.jpg

Anyway, these are pretty impressive plans. I'd suggest a few optimisations:

- The motorway junction should be teardropped, like M4 J19, allowing more capacity to/from the airport.
- The south terminal junction could also be teardropped.
- There is a very tight weaving space (<300m) on the eastbound Airport Way between the merge from London Rd and the new GSJ at the south terminal. They could extend the slip from London Rd all the way to the new GSJ, or fold the eastbound slips at the GSJ to the east (e.g., as a compact trumpet).
- At the north terminal, the new signalised t-junction on London Rd could have a couple of extra freeflow filters bypassing the lights for terminal to northbound and southbound to Airport Way.

I also drew up a more radical north terminal design that provides freeflow for Airport Way to/from the terminal and Airport Way to/from London Road (north). It still only uses one new bridge.

Gatwick north term - Copy.jpg
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Re: Gatwick Airport's Highway improvements (A23/M23/A217)

Post by jervi »

jackal wrote: Thu Sep 09, 2021 14:33 Anyway, these are pretty impressive plans. I'd suggest a few optimisations:

- The motorway junction should be teardropped, like M4 J19, allowing more capacity to/from the airport.
- The south terminal junction could also be teardropped.
- There is a very tight weaving space (<300m) on the eastbound Airport Way between the merge from London Rd and the new GSJ at the south terminal. They could extend the slip from London Rd all the way to the new GSJ, or fold the eastbound slips at the GSJ to the east (e.g., as a compact trumpet).
- At the north terminal, the new signalised t-junction on London Rd could have a couple of extra freeflow filters bypassing the lights for terminal to northbound and southbound to Airport Way.

I also drew up a more radical north terminal design that provides freeflow for Airport Way to/from the terminal and Airport Way to/from London Road (north). It still only uses one new bridge.
- I agree with your first two points, apart from u-turning traffic there is zero point of providing a roundabout when a teardrop can achieve the same but more efficient and safer.
- I measured the weaving space to be 275m, so not a lot of room at all. Airport Way will be limited to 40mph, so 275m @ 40mph = 15 seconds which is not okay, but at least its not a lane drop/gain. Having a C/D carriageway I can't see fixing the issue, plus would require new bridge(s) over the railway which is costly. Maybe some sort of ramp metering is needed like at Redbridge?
- The proposed layout near the Northern Terminal I doubt will be its final design. I'd prefer the other options which would of made it into a fairly standard roundabout interchange. This would only require 1 D2 bridge, but would involve extensive earthworks. It would be simpler to use than a mess of current or proposed.
alt north term-min.PNG
Options are listed here: https://www.gatwickairport.com/globalas ... part-5.pdf

Your design for North Terminal Junction seems sufficient, although I'd merge Longbridge Way into Northway prior to the roundabout as that would allow access to A23 (London Road) South without having to U-turn at Longbridge
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Re: Gatwick Airport's Highway improvements (A23/M23/A217)

Post by jackal »

Dear God, anything but a signal-controlled merge!

I had something like this in mind:

Gatwick South Terminal - Copy.jpg

Removes the weaving and the prohibited movement is a duplicate anyway. A new railway bridge (or widening of the existing one) is just the price of entry :D

From the document you linked it seems the South Terminal roundabout may be 'for but not with' a link on the north side to new developments. That may explain the lack of teardrop there, though there's not really any excuse at the motorway junction.

The alternative North Terminal design is neat but points all the freeflow at the A23 London Rd, which rapidly hits a roundabout. I'm not sure it's better than the design at consultation, which actually improves on the current freeflow into the South Terminal.

None of the designs bear much resemblance to the road network proposed in 2014 as part of second runway plans:

Gatwick - Copy.PNG

Detail of area now proposed for improvement:

Gatwick detail - Copy.PNG
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Re: Gatwick Airport's Highway improvements (A23/M23/A217)

Post by M19 »

R&B Council have allocated an employment site to the north with access from the J9a roundabout that should be recognised in the proposals but are missing.
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Re: Gatwick Airport's Highway improvements (A23/M23/A217)

Post by Phil »

jackal wrote: Thu Sep 09, 2021 20:37 Dear God, anything but a signal-controlled merge!

I had something like this in mind:


Gatwick South Terminal - Copy.jpg


Removes the weaving and the prohibited movement is a duplicate anyway. A new railway bridge (or widening of the existing one) is just the price of entry :D

From the document you linked it seems the South Terminal roundabout may be 'for but not with' a link on the north side to new developments. That may explain the lack of teardrop there, though there's not really any excuse at the motorway junction.

The alternative North Terminal design is neat but points all the freeflow at the A23 London Rd, which rapidly hits a roundabout. I'm not sure it's better than the design at consultation, which actually improves on the current freeflow into the South Terminal.

None of the designs bear much resemblance to the road network proposed in 2014 as part of second runway plans:


Gatwick - Copy.PNG


Detail of area now proposed for improvement:


Gatwick detail - Copy.PNG
Indeed - but you should take note the 2nd runway plans have changed significantly too!

To recap...

The PRE COVID PLAN was for a completely new full length runway and terminal to the south of the current one involving huge alterations to massively expanding the airports footprint to increase airport capacity and take on Heathrows 3rd runway plan head on - and just as with Heathrow huge highway changes were needed to support the plan.


The POST COVID PLAN is much, much less ambitious! Its simply a case of shifting the 'emergency runway' / taxiway north by a few meters thus meeting the minimum standard for parallel use. Some minoor alterations on the airfield and the building of a few more stands plus hotel and office space (not quite sure why thats a good move given how many offices are struggling for tenents these days). Crucially, as with 'Smart Motorway upgrades' this latest plane can all be done within the existing airport boundary a nd the net result is the highway changes needed to support it are much much less.
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Re: Gatwick Airport's Highway improvements (A23/M23/A217)

Post by Phil »

M19 wrote: Fri Sep 10, 2021 18:59 R&B Council have allocated an employment site to the north with access from the J9a roundabout that should be recognised in the proposals but are missing.
The area north of the A23 - M23 link is administered by Surrey CC / Reigate & Banstead BC / Horley TC. Gatwick Airport and the roads apart from Longbridge roundabout) lie in West Sussex / Crawley BC territory

Given the planning authority for any Gatwick developments will mostly be Crawley BC (who will naturally want any 'industrial development to be in their town and not R&B) and the 9A roundabout is national Highways for Englands remit then its not a surprise said 'industrial development' is absent from the plans.
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Re: Gatwick Airport's Highway improvements (A23/M23/A217)

Post by Micro The Maniac »

Dumb question:

Given that my OCD triggers at two roads with the same number that don't actually properly join (A23, yes, I'm talking about you here), and given that the Perimeter Road gives prohibited traffic access between the two terminals, is there any reason that Airport Way (once the flyover is in place) could not be M23 spur (or M230?) all the way in?
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Re: Gatwick Airport's Highway improvements (A23/M23/A217)

Post by jervi »

Micro The Maniac wrote: Mon Sep 13, 2021 08:28 Dumb question:

Given that my OCD triggers at two roads with the same number that don't actually properly join (A23, yes, I'm talking about you here), and given that the Perimeter Road gives prohibited traffic access between the two terminals, is there any reason that Airport Way (once the flyover is in place) could not be M23 spur (or M230?) all the way in?
It very much annoys me too!
Looking at various maps during and shortly after the construction on the M23, they all show the spur incorrectly which leads me to believe that Airport Way was very much a botch.
Some maps show the whole spur as an A road Dual Carriageway, whilst others show both the Southern terminal roundabout & Northern terminal roundabouts as GSJs & Airport Way being a motorway.

As part of these proposals, the speed limit West of J9a will be 40mph (currently its a mixture of 50mph/nsl), and designating a motorway with a fixed speed limit of 40mph isn't exactly ideal.
Whilst there is access to the Southern terminal for NMUs from the Perimeter road & NCN21, access to the other side of the railway is limited. Currently there are three access points: J9a, Public Footpath entrances from B2036 & A footbridge (stairs only) over the railway south of the station. So if Airport Way was restricted to ban NMU (or become a motorway) then an alternative crossing of the railway would be required to allow cycles to cross.

So in short, I'd highly doubt the M23 Spur being extended beyond J9a (except by a few 100m to cover the start of the flyover). I'd also doubt any NMU restrictions would be applied to Airport Way, although potentially pedestrians could be banned from parts.

I think its more likely that the M23 Spur will be de-motorway'd, at which point Airport Way & M23 spur could get its own number. Especially since it will no longer have a hard shoulder and will have a fixed speed limit of 50mph/40mph, plus this could open up development off J9's Eastern side.
Last edited by jervi on Mon Sep 13, 2021 12:50, edited 1 time in total.
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Re: Gatwick Airport's Highway improvements (A23/M23/A217)

Post by Micro The Maniac »

jervi wrote: Mon Sep 13, 2021 09:08 I think its more likely that the M23 Spur will be de-motorway'd, at which point Airport Way & M23 spur could get its own number. Especially since it will no longer have a hard shoulder and will have a fixed speed limit of 50mph/40mph, plus this could opened up development off J9's Eastern side.
Ummm... given J9 is a roundabout that is one option!
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Re: Gatwick Airport's Highway improvements (A23/M23/A217)

Post by Bryn666 »

Micro The Maniac wrote: Mon Sep 13, 2021 12:23
jervi wrote: Mon Sep 13, 2021 09:08 I think its more likely that the M23 Spur will be de-motorway'd, at which point Airport Way & M23 spur could get its own number. Especially since it will no longer have a hard shoulder and will have a fixed speed limit of 50mph/40mph, plus this could opened up development off J9's Eastern side.
Ummm... given J9 is a roundabout that is one option!
Sadly the most likely one too. Designating new motorways seems to cause National England Agency for Departmental Highways of Transport a rash.
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Re: Gatwick Airport's Highway improvements (A23/M23/A217)

Post by Chris_533976 »

Phil wrote: Mon Sep 13, 2021 02:18
jackal wrote: Thu Sep 09, 2021 20:37 Dear God, anything but a signal-controlled merge!

I had something like this in mind:


Gatwick South Terminal - Copy.jpg


Removes the weaving and the prohibited movement is a duplicate anyway. A new railway bridge (or widening of the existing one) is just the price of entry :D

From the document you linked it seems the South Terminal roundabout may be 'for but not with' a link on the north side to new developments. That may explain the lack of teardrop there, though there's not really any excuse at the motorway junction.

The alternative North Terminal design is neat but points all the freeflow at the A23 London Rd, which rapidly hits a roundabout. I'm not sure it's better than the design at consultation, which actually improves on the current freeflow into the South Terminal.

None of the designs bear much resemblance to the road network proposed in 2014 as part of second runway plans:


Gatwick - Copy.PNG


Detail of area now proposed for improvement:


Gatwick detail - Copy.PNG
Indeed - but you should take note the 2nd runway plans have changed significantly too!

To recap...

The PRE COVID PLAN was for a completely new full length runway and terminal to the south of the current one involving huge alterations to massively expanding the airports footprint to increase airport capacity and take on Heathrows 3rd runway plan head on - and just as with Heathrow huge highway changes were needed to support the plan.


The POST COVID PLAN is much, much less ambitious! Its simply a case of shifting the 'emergency runway' / taxiway north by a few meters thus meeting the minimum standard for parallel use. Some minoor alterations on the airfield and the building of a few more stands plus hotel and office space (not quite sure why thats a good move given how many offices are struggling for tenents these days). Crucially, as with 'Smart Motorway upgrades' this latest plane can all be done within the existing airport boundary a nd the net result is the highway changes needed to support it are much much less.
I think the PRE COVID PLAN got dropped a goodly bit before COVID came along. As far as I can remember, what you call the POST COVID PLAN, moving the emergency runway to become a proper second runway, was proposed pre March 2020. They realised they could do it really quite cheaply and can get around most of the problems Heathrow were encountering. And well, stick one up at Heathrow!
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Re: Gatwick Airport's Highway improvements (A23/M23/A217)

Post by jervi »

Second consultation on Northern Runway Plans at Gatwick due to start mid June.
https://www.gatwickairport.com/business ... rn-runway/
The page does state that it "includes changes to our plans for office buildings, hotels, car parking, flood alleviation and airport layout". It doesn't explicitly say anything about surface access, although the local rag (theArgus) say
"Roads around the airport would also have changes, including the addition of a new lane westbound over the Brighton main rail lane and a third lane to the A23 approaching Longbridge roundabout." - Although I think the journalist is just making things up since a new Westbound lane over the BML is pointless.
https://www.theargus.co.uk/news/2016779 ... nd-runway/
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Re: Gatwick Airport's Highway improvements (A23/M23/A217)

Post by Peter Freeman »

jackal wrote: Thu Sep 09, 2021 20:37 Dear God, anything but a signal-controlled merge!
Yes, not here; but they can sometimes be justified. The Redbridge example that's referenced seems justified, since there is little space for proper merging, and it precedes a too-short weave length. I think there used to be one on the north side of Erskine Bridge M898?
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Re: Gatwick Airport's Highway improvements (A23/M23/A217)

Post by jackal »

Peter Freeman wrote: Thu May 26, 2022 17:38
jackal wrote: Thu Sep 09, 2021 20:37 Dear God, anything but a signal-controlled merge!
Yes, not here; but they can sometimes be justified. The Redbridge example that's referenced seems justified, since there is little space for proper merging, and it precedes a too-short weave length. I think there used to be one on the north side of Erskine Bridge M898?
Redbridge is dubious IMO. It should just be a 1+1 freeflow lane gain. At 40mph a 300m weave is just about doable. If we signalised every dubious legacy weaving space Glasgow would grind to a halt for starters.
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Re: Gatwick Airport's Highway improvements (A23/M23/A217)

Post by Peter Freeman »

^ On reflection, I agree, regarding Redbridge. I hadn't noticed the 40mph sign. Low-speed operation makes a big difference. I would argue that it should be employed more often to alleviate danger-spots, as is obviously the intention here.
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Re: Gatwick Airport's Highway improvements (A23/M23/A217)

Post by jackal »

Peter Freeman wrote: Fri May 27, 2022 13:51 ^ On reflection, I agree, regarding Redbridge. I hadn't noticed the 40mph sign. Low-speed operation makes a big difference. I would argue that it should be employed more often to alleviate danger-spots, as is obviously the intention here.
Indeed speed is a fundamental parameter for weaving along with flows. DMRB has some figures for that:

Weaving lengths - Copy.JPG
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Re: Gatwick Airport's Highway improvements (A23/M23/A217)

Post by Peter Freeman »

^ Interesting graphs, thanks. Since the situation in question fits easily within the weaving guideline, I wonder why they chose the signals option. It's not like the UK to miss out on an opportunity to hatch-out a lane or two ...! Could it be that the input from that (originally-3-lane) roundabout exit was initially expected to be much higher? But of course, it still couldn't be high enough to exceed that guideline, at 64km/hr.
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Re: Gatwick Airport's Highway improvements (A23/M23/A217)

Post by Peter Freeman »

^ With apologies for prolonging this off-topic digression, here's an interesting AU example of such a signalised 'merge'.

https://www.google.com.au/maps/@-37.902 ... a=!3m1!1e3

This location used to be a simple lane-add merge (2+1=3) of M1's off-ramp into eastbound Ferntree Gully Road. It lay 300m upstream of a signalised intersection of two major D3 roads. The crossroads' queue often reached right back to this merge, causing major peak-hour congestion, with queueing extending back onto the freeway ramp. This previous layout may be seen a few steps backwards in Google Earth historical.

About three years ago, the merge was replaced by this signalised intersection. Counter-intuitively, the problem was resolved. Both the crossroads queue and the ramp queue are now more orderly and shorter.

Both shorter?! How can this be? Explanation: the previous single lane of added traffic in the left lane of FTG Road included vehicles intending to turn right at the downstream intersection. The whole 300m queue was therefore disrupted by drivers needing to perform three lane-swaps to the right (and the converse), and so, although the crossroads design is ok and its signals operate correctly, the queue couldn't move as fast as required to be efficient. Now however, whenever the signals give a green to either of the merge inputs, all three lanes of traffic flow quickly into the queue, either already in their best lane or able to immediately select it.

It was a weaving problem of course, but not on a motorway, and not casually obvious. The original layout was from many years ago, when the idea that free-flow was the answer to everything was even more prevalent than it is now. There do exist many situations where available road surface is more efficiently utilised under signalisation.
Last edited by Peter Freeman on Mon May 30, 2022 05:34, edited 1 time in total.
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Re: Gatwick Airport's Highway improvements (A23/M23/A217)

Post by jackal »

There was a similar signalisation on the westbound A414 merge here about 15 years ago. Previously it was a 1+1 freeflow lane gain. The merge was moved closer to the at-grade junction as the result of the addition of C/D lanes to the M1, which seemingly triggered the signalisation. The at-grade junction is less substantial than in the Australian example, so I don't know if there were significant weaving issues - most traffic would just head straight over at the roundabout.
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