M2 junction 5 improvements

[jackal]

Not sure if there's a thread about this already, but HE plans to 'reduce congestion at the junction through improvements to slip roads and enhanced junction approaches', with construction to start by Spring 2020.

From the scheme description I'd assumed it would just be the usual stacking space etc. But the estimated cost is now listed as £50m-100m, which is more than the likes of the M6 J19 scheme and in line with the seemingly ambitious M3 J9. It could just be that this is what it costs to do a bog standard upgrade, given the M2 is on a viaduct here, but maybe something a little more interesting is possible.

As '[t]he approach to the junction from the north and east, in particular, experiences high levels of delay', a good option would be grade separation of the roundabout to separate these flows. I admit that would be an optimistic interpretation of 'improvements to slip roads and enhanced junction approaches' but surely replacing a flat roundabout with a simple two-level GSJ would be possible for £50m-100m, and provide much more benefit than merely widening the approaches?

[KeithW]

That junction really is one of those where you wonder what they were thinking about when they designed it. I used it a couple of times to get to Sheerness and heading that way having come off the M2 Southbound wasn't too bad but if you wanted to take the road to Maidstone it was a nightmare as the entry to the roundabout was acute and the sight lines poor. Given that the M2 is at a higher level than the A249 it would seem to be an obvious place to use a GSJ in the first place.

[Truvelo]

This is what I came up with many years ago. Everything is freeflow apart from both right turns onto the A249 which would have to be signalised.

[Bryn666]

That is fine as the signals only require two stages as well so can run short greens to keep queues down.

The earthworks aren't going to be a nightmare though are they for the new slips? You could perhaps sacrifice some of the geometry to reduce imported material but who knows.

Either way we know Highways England won't promote anything that might upset well to do NIMBY types so I am ruling out new slips.

[jackal]

It may be difficult to cut off access to Maidstone Road as per Truvelo's plan as that would significantly restrict access to Danaway and the like.

The dedicated left turns for A249sb->M2eb and A249nb->M2wb are very good ideas though. This removes the current issue where, due to the folded slips, 'left' turners presently have to turn right at the roundabout.

[Chris5156]

As '[t]he approach to the junction from the north and east, in particular, experiences high levels of delay', a good option would be grade separation of the roundabout to separate these flows. I admit that would be an optimistic interpretation of 'improvements to slip roads and enhanced junction approaches' but surely replacing a flat roundabout with a simple two-level GSJ would be possible for £50m-100m, and provide much more benefit than merely widening the approaches?

I absolutely agree - grade separating the roundabout is definitely the right way forward.

Look, it's easy!

stockbury.png (26.2 KiB) Viewed 13132 times

[Bryn666]

Don't give them ideas...

[frediculous_biggs]

I wrote a long message about this at lunch time that didn't seem to submit. It was similar to the below:

However, I think it wouldn't be too difficult to GSJ the junction. Although in a valley, it is quite wide and the M2 is very high up. However, some of the sliproads are tight in joining the existing roundabout, so I wonder how that would work with a wider one.

Removing the access to Danaway would allow A249 S -> M2 E traffic to avoid the roundabout, but is a very useful cut through from Newington.

One thing that definitely needs to be improved are the joins to the the M2. These are far too short and tight. Little can be done about the tightness, but the lengths can be extended. Certainly HGVs struggle with both the gradients and curves and often end up joining the mainline at around 30mph. This, coupled with the weight of traffic joining the M2, often means most users have to move out to the right, effectively reducing the M2 to 1 lane through the junction.

Incidentally, any reasonably heavy amount of rain and the hard shoulder of the bridge floods. Only a few years back did they remove the rut over the bridge in Lane 2 heading Westbound that would trap my car's wheels in it, like cart tracks.

[jackal]

As '[t]he approach to the junction from the north and east, in particular, experiences high levels of delay', a good option would be grade separation of the roundabout to separate these flows. I admit that would be an optimistic interpretation of 'improvements to slip roads and enhanced junction approaches' but surely replacing a flat roundabout with a simple two-level GSJ would be possible for £50m-100m, and provide much more benefit than merely widening the approaches?

I absolutely agree - grade separating the roundabout is definitely the right way forward.

Look, it's easy!
stockbury.png

Beautiful

[Brenley Corner]

I may have dreamt this or just made it up as I've sat in traffic there, but I have got the idea that the rough plan is a southbound only flyover on the A249. There is a queue southbound from the Isle of Sheppey to the Stockbury roundabout in both rush hours that most days goes back at least 1 or 2 miles - and a lot of it is heading onwards towards Maidstone. The signals on the roundabout don't help and when there was a major failure that lasted weeks a year or two back the traffic flowed much better in the rush hours from the busier arms of the roundabout. You cannot cut off the old road as it provides a relief to the A249 and a diversion when there are accidents - and there is an accident hotspot right under the M2!!

Tony

[Gareth Thomas]

There is a queue southbound from the Isle of Sheppey to the Stockbury roundabout in both rush hours that most days goes back at least 1 or 2 miles

Yes, it is ALWAYS mentioned on both KMFM and Heart travel news in the morning. I'm sure the presenters must be bored of saying it by now.

I doubt much will be done to the junction due to the topography but I suppose at least a southbound flyover on the A249 could help.

[jackal]

Consultation is due in the Autumn: http://roads.highways.gov.uk/projects/m ... rovements/

[MotorwayPlannerM21]

This is how I would improve the junction, using much of the existing layout:

The roundabout to the north handles Maidstone Road and access onto the M2 whilst the existing roundabout is removed. This does have 2 extra slip roads but it freeflows the necessary movements (M2 w/b - A249 s/b and A249 n/b - M2 e/b)

[jackal]

Consultation now open. The design isn't too bad but I'd have preferred the version with the A249 flyover.

https://highwaysengland.citizenspace.co ... rovements/

[Bryn666]

I see they had to have an example to prove they are still worshipping the God of DMRB... a three level roundabout.

I think the flyover option would have made more sense than another hamburger. They're limited in effectiveness yet keep appearing as a design.

[jackal]

The problem is the flyover version of that design is some £158m. But I'd have liked to see an option with just the flyover, i.e. without the other new freeflow connections and moving the local road, which account for a lot of the cost.

The version of the flyover design (option 4) in the TAR has a few more bells and whistles, presumably removed for cost:

There was also a dumbell considered (option 8), again no doubt far beyond the scheme budget:

In addition, option 11, 'a fully free-flowing interchange between the A249 and the M2', is mentioned as 'the top-end design in terms of cost and successfulness but local connectivity is not taken into account in this option, and with substantial land take requirements it was seen as unsuitable. However, if a purely strategic solution is required it could be considered'. Sadly there is no drawing (maybe an FOI would solve that).

[Bryn666]

The realignment of the local road has a seemingly pointless flyover on it too.

Again we see the useful things abandoned in favour of completely unnecessary ones. I'm getting very frustrated at this.

[Chris5156]

The problem is the flyover version of that design is some £158m. But I'd have liked to see an option with just the flyover, i.e. without the other new freeflow connections and moving the local road, which account for a lot of the cost.

Moving the local road makes a significant gain, which is the ability to free-flow the southbound-to-westbound movement. The unusual layout of the sliproads means that two simple left-turns past the roundabout are all that's needed to freeflow the two right-turns off the A249, providing the local road is relocated.

I'm sure, though, that a local road could connect to the roundabout between the M2 westbound off-slip and the A249 southbound on-slip without requiring extensive new roads and flyovers.

[jackal]

Yes, I get why they moved the local road, I'm just saying that losing the A249 flyover is not a price worth paying to get that extra freeflow right turn in.

This seems to be supported by the movement volumes at the junction. The A249<->A249 movements come to 18,795, compared to 9,586 for A249sb>M2wb.

(Be careful reading this - due to the strange junction design, right turns look like left turns!)

[jackal]

The realignment of the local road has a seemingly pointless flyover on it too.

That really is bizarre. As the brochure shows, the rejected options 4 and 12 achieve a similar local road solution without the extra structure.