N40 - Douglas Flyover widening

marno21

This is something that gets discussed repeated in the N40 motorway reclassification and the Dunkettle/M28 threads, regarding the Douglas flyover and the significant constraint it places on the N40, let alone what it'll be like when the M28 and Dunkettle are operational.

Here's a thread to discuss the issue.

05eaftqbrs9jlh

They'd want to fix those two sections in the middle of the flyover where you fall down for a second and it feels like the road is going to come out from under you. Also there's the whole "tackling obesity by loosening your belt" argument about widening the roads without investing in public transport. Hardly any buses go out that way, the options are rubbish between both ends of the southside. Not to mention the fact that there's no cycling route where you can safely travel from Douglas/Turners Cross to Bishopstown, you have to go on narrow, hilly main roads penned in by dangerous junctions. Or you can cycle on the Link, if you're sick of the traffic and just want to die.

350125GO!

(Copy & paste from M40 thread)

Better to remove and rebuild...

https://www.steelconstruction.info/L...posite_bridges

It would be better to remove as much of that 'wall' through Douglas village and the widen / renaturalise the river culvert.

https://restorerivers.eu/wiki/index....in_Hondouville

https://www.therrc.co.uk › lrapPDF
the london rivers action plan - the River Restoration Centre

ianobrien

Widening it to 3 lanes makes sense on the surface but given our shocking lane discipline, it won't increase the capacity by 50%. Lanes 2 & 3 would be full, with lane 1 practically empty.

I would widen it heading West from Bloomfield but have lane 1 as a M28 merge lane until well past the RPH (to get merging traffic up to speed). I'd then have lane 1 heading for the airport and lanes 2&3 heading along the N40 (as it is now).

For widening at Douglas Shopping Center, there are plenty of engineering solutions to elevate the extra lane over the access road below.

Widening heading East could be more trouble due to a few houses near the road.

Then again, I won't see it. I'll be dead and gone before they do it!

marno21

ianobrien wrote: »

Widening it to 3 lanes makes sense on the surface but given our shocking lane discipline, it won't increase the capacity by 50%. Lanes 2 & 3 would be full, with lane 1 practically empty.

I would widen it heading West from Bloomfield but have lane 1 as a M28 merge lane until well past the RPH (to get merging traffic up to speed). I'd then have lane 1 heading for the airport and lanes 2&3 heading along the N40 (as it is now).

For widening at Douglas Shopping Center, there are plenty of engineering solutions to elevate the extra lane over the access road below.

Widening heading East could be more trouble due to a few houses near the road.

Then again, I won't see it. I'll be dead and gone before they do it!

Agreed. It would be best to lengthen the N28 merging lane until well after where it currently ends, and keep N28 traffic in there where possible, which would solve some of the lane discipline issue.

I wouldn't be too concerned about adding an additional lane eastbound given the bottleneck further on at the tunnel, but it would be useful if there was a third lane between Douglas and the N28 exit.

Were you to widen on the shopping centre a sufficient amount to shift the entire road to the south to allow 3 lanes in either direction, it would make retaining the Douglas West on ramp an issue given the space constraints there, the river and the industrial buildings.

AugustusMinimus

I still would add another lane east bound between Douglas and Bloomfield. Would help a lot I think.

Markcheese

Should we be thinking about giving an alternative to cars on the n40 ... Add an extra regular traffic lane you'll get maybe an extra 15 ,% capacity ( except when it's bumper to bumper and then it's a car park ) , so maybe a high frequency bus lane ,possibly a decent bike path next to the motorway ,
All of which would free up the n40 for me to drive my van stress free any time ...

Chris_5339762

Yes but the big problem that is coming down the lines is going to be the same as the M9/7 junction and the Naas Bypass widening in Dublin. You have 2x two lane motorways merging into one two lane motorway which then becomes a 3 lane motorway further along.

Once Dunkettle is done and unblocked, and the M28 is done, you'll have two two lane motorways merging into a single two lane motorway that goes over the Douglas Viaduct, then widens to three lanes less than a mile later.

Its going to be the worst bottleneck in the country when Dunkettle and the M28 are done, and yet no-one seems to realise this. I predict traffic backed up to the tunnel from Day 1.... what they are planning just isn't going to work.

Widen the viaduct to three lanes each direction, kill off the Douglas east exit eastbound, take a bit of land from the astroturf pitches so that one Douglas junction and a link road to east is created. Demolish the electricity substation and you have enough land for this with a slight widening towards the burnt shopping center.

mydiscworld

I think they will also need to extend a queueing lane to get onto the Mahon Point slip road.

Once Dunkettle is free flow, traffic will get backed up on the ramp to get over the Mahon Point exit bridge. If it backs up to the main road, traffic will back up into tunnel and cause accidents.