M23 junctions 8 to 10: smart motorway

[jervi]

https://www.youtube.com/watch?v=rmM-eTzx46M
Here's what it look liked today. Also went along the spur.
The 1 ERA on the Spur is a total joke (5:05), also what do people think of the arrangement at J9 (3:50)

[Truvelo]

The spur is 3 lanes towards the airport and 2 lanes towards the M23. Obviously more passengers fly out of Gatwick than land

[Bryn666]

The spur is 3 lanes towards the airport and 2 lanes towards the M23. Obviously more passengers fly out of Gatwick than land

It'll be the higher capacity of the big J9 roundabout measured against the whatever the knot of slip roads and tiny roundabouts the western end calls itself.

[A320Driver]

The spur is 3 lanes towards the airport and 2 lanes towards the M23. Obviously more passengers fly out of Gatwick than land

It'll be the higher capacity of the big J9 roundabout measured against the whatever the knot of slip roads and tiny roundabouts the western end calls itself.

I’d hardly call the western end ‘tiny’. It has the same number of arms as the J9 roundabout.

And we also have our newest botched roadsign at 3:30 - “2/3 miles” [two thirds]

[Phil]

The spur is 3 lanes towards the airport and 2 lanes towards the M23. Obviously more passengers fly out of Gatwick than land

I believe that the main reason for doing this has more to do with the fact that when traffic is held up in the past people have taken to using the hard shoulder as some sort of impromptu airport drop off location in a desperate attempt to avoid missing their flight. I guess the thinking is it won't be so easy if its full of cars.

Of course if such queues do develop, 3 lanes does give more stacking space and prevent it tailing back onto the M23 itself.

[Phil]

https://www.youtube.com/watch?v=rmM-eTzx46M
Here's what it look liked today. Also went along the spur.
The 1 ERA on the Spur is a total joke (5:05), also what do people think of the arrangement at J9 (3:50)

That ERA is the tiny remaining bit of hard shoulder.

In the early 1990s the immediate approach to the Airport roundabout was widened from 2 to 3 lanes - and because this was pre SMART motorways this widening meant that a new length of hard shoulder (no more than 50 yards) was provided.

They could have dug it up under the current works - but I guess someone saw it and decided to use it for an ERA even though its right at the end of the spur rather than in the more logical place half way down (but that option would have needed extensive civil works to widen the carageway.....)

[Phil]

I understand (through vague references in Highways England leaflets) that the left turns at J9 are getting a significant upgrade. Is there any evidence of this?

I know most people don't agree with Highways England's theory that hard shoulders are a bad idea, and I know the timekeeping has been shonky, but with the significant widening at the M25 exit, the new emergency exits and the possible J9 works, they've been quite thorough with what seemed like a rather mundane project.

The diverge and merge setup at the M25 junction is the best I have seen anywhere in the country so far its not all squashed together and gives plenty of space for traffic to separate and join up without getting in the way of each other.

[jervi]

https://www.youtube.com/watch?v=rmM-eTzx46M
Here's what it look liked today. Also went along the spur.
The 1 ERA on the Spur is a total joke (5:05), also what do people think of the arrangement at J9 (3:50)

That ERA is the tiny remaining bit of hard shoulder.

In the early 1990s the immediate approach to the Airport roundabout was widened from 2 to 3 lanes - and because this was pre SMART motorways this widening meant that a new length of hard shoulder (no more than 50 yards) was provided.

They could have dug it up under the current works - but I guess someone saw it and decided to use it for an ERA even though its right at the end of the spur rather than in the more logical place half way down (but that option would have needed extensive civil works to widen the carageway.....)

It does very much look like that, It appears the the kerb hasn't moved at all (as the lighting columns appear to be in the same place as pre works). However it does seem that this ERA doesn't meet the specs. The DLS appear to be at the start of the ERA (facing 90 degrees to the carriageway), you can't see the sign if you are stopped there. I though that DLS are required to be either in the centre of the ERA facing the carriageway, or at the far end of the ERA facing 90 degress. Also the width of ERAs are noticeably wider than a Hard Shoulder. It would be interesting to see whether that width was achieved, maybe because it is limited to 50 mph and the 85th percentile speed immediately before the roundabout is unlikely to be above 40 mph, so it didn't have to meet the standards of 70 mph? It would off been better if they just left it has a hard shoulder, plus would reduce signage

[jervi]

Just noticed from my video that the new sign on the approach to J9a from the M23 Spur is wrong.
https://youtu.be/rmM-eTzx46M?t=224
Why is it showing two arms to the North? - Surely an at-grade roundabout just shows one arm. I presume it might be like this as approach from the A23 Spur has destinations for a u-turn, and whoever made the sign got a little confused. It wasn't like this before

Also the approach from the airport terminal shows J9a as a GSJ, but that's on private property, so i'll let them off here

[jackal]

Bravo for the new filter lane off the northbound offslip at J9, removing the unnecessary signals there, and also for not butchering the existing one at J9 (sadly not a foregone conclusion nowadays). You could argue that the offslip should ONLY lead to the filter lane, but still it's good to see an ALR scheme providing genuine junction improvements too. (See jervi's video from 3.18.)

[WHBM]

It'll be the higher capacity of the big J9 roundabout measured against the whatever the knot of slip roads and tiny roundabouts the western end calls itself.

There is a history of traffic into the airport blocking back (from beyond the terminal roundabout) right onto the M23, but never knew of such an instance leaving. The extra lane gives more ability to stack.

Have to say I don't like the northbound exit ramp, with both lanes equally signed for Gatwick, then lane 1 is freeflow and lane 2 suddenly a Give Way. The advance signage of freeflow to the left does not make this apparent. What do others think ?

Removal of the hard shoulder approaching this (and other) airports is possibly trying to overcome a compliance issue, it has long been something where drivers stop there to get tickets out to check which terminal, or to wait away from the paid parking until those they are picking up arrive, and in recent times has got significantly worse with Uber etc hanging about on the shoulder there waiting for a call.

[Jayck]

You could argue that the offslip should ONLY lead to the filter lane, but still it's good to see an ALR scheme providing genuine junction improvements too. (See jervi's video from 3.18.)

You're right about it only needing to lead to the filter lane, the right hand lane road marking even has a left turn arrow directing traffic towards Gatwick. What's the logic here I wonder? In theory we don't even need a full roundabout. The roundabout lanes between the spur road access shouldn't need to exist, as per the semi-roundabout at the M32/M4 junction.

[Bryn666]

Have to say I don't like the northbound exit ramp, with both lanes equally signed for Gatwick, then lane 1 is freeflow and lane 2 suddenly a Give Way. The advance signage of freeflow to the left does not make this apparent. What do others think ?

It is not obvious that the right hand lane on the slip road is a give way until you're up near the top. A couple of extra signs showing this would help.

Here's how I signed an identical scenario on the A556: https://goo.gl/maps/6B6WdgdyTytTJLD1A (looks like a lane marking has been lost in translation mind).

[jackal]

You could argue that the offslip should ONLY lead to the filter lane, but still it's good to see an ALR scheme providing genuine junction improvements too. (See jervi's video from 3.18.)

You're right about it only needing to lead to the filter lane, the right hand lane road marking even has a left turn arrow directing traffic towards Gatwick. What's the logic here I wonder? In theory we don't even need a full roundabout. The roundabout lanes between the spur road access shouldn't need to exist, as per the semi-roundabout at the M32/M4 junction.

I guess they think a one lane filter isn't enough and a two lane filter would be too much as it only leaves one lane for traffic off the roundabout. I still think the benefit of making it freeflow is great enough that they should have gone with it. By giving drivers a give way to navigate and the choice (which they should never use) to go round the roundabout you're introducing an unnecessary conflict and confusion.

[jervi]

You could argue that the offslip should ONLY lead to the filter lane, but still it's good to see an ALR scheme providing genuine junction improvements too. (See jervi's video from 3.18.)

You're right about it only needing to lead to the filter lane, the right hand lane road marking even has a left turn arrow directing traffic towards Gatwick. What's the logic here I wonder? In theory we don't even need a full roundabout. The roundabout lanes between the spur road access shouldn't need to exist, as per the semi-roundabout at the M32/M4 junction.

I guess they think a one lane filter isn't enough and a two lane filter would be too much as it only leaves one lane for traffic off the roundabout. I still think the benefit of making it freeflow is great enough that they should have gone with it. By giving drivers a give way to navigate and the choice (which they should never use) to go round the roundabout you're introducing an unnecessary conflict and confusion.

I think both lanes should of had protect freeflow (remove access to roundabout), then have traffic from Southbound exit to merge into 1 lane on the southernly bridge to then become lane 3 on the spur.
But still allow two lanes of traffic on the southbound off slip to allow for a greater stacking capacity, but then merge to one as said above.
Mitigations would have to be in place to allow traffic patrol vehicles to carry out u-turns, especially southbound -> northbound.
Also HGVs would have to be allowed to be in Lane 3, as that's how they would enter the spur, how shouldn't be too much of an issue since the speed limit is 50mph & most HGVs would be heading to the Air Cargo Terminal which means they need to be in Lane 2 (or 3) at J9a

[MotorwayPlannerM21]

If both lanes went to the spur, there'd be no option for traffic to turn round if it needs to. Also, presumably, more traffic will be coming from the north than south (coming from the M25), so this should really retain two lanes.

[jervi]

https://www.legislation.gov.uk/uksi/202 ... 721_en.pdf
Fixed 50mph speed limit for the gatwick spur has had its legislation passed.
However it doesn't clearly state if it is east & west bound or just westbound.
I'd presume it is strictly talking about westbound, as that is what was consulted on and appears in the document three times (in what has happened during the scheme), however nothing to say it is ONLY westbound.

[Vierwielen]

The spur is 3 lanes towards the airport and 2 lanes towards the M23. Obviously more passengers fly out of Gatwick than land

Unless they are trying to clear excess traffic from the M23 quickly, but trying to throttle it going onto the M23.

[Vierwielen]

The spur is 3 lanes towards the airport and 2 lanes towards the M23. Obviously more passengers fly out of Gatwick than land

If the government ever gets it into their head to move over to driving on the right , this will be one of the many problems that they will face.

[WHBM]

Why all this concern about the odd u-turner. If it had been built as a proper Trumpet of Freeflow junction, as in many places elsewhere, there would be no such facility anyway. It's just half a mile down the spur to the next roundabout, and back again.

Regarding 3 lanes in, 2 lanes out, that is quite reasonable. Layouts do not HAVE to be symmetrical. Hence why London Underground commonly have three escalators at a station, one running in and two out ?