What work could or should happen in conjunction with the planned Portishead reopening?

[Ashley Hill]

Moderator note: Split from

Portishead approved

The Portishead scheme has been approved. Background details and link to decision in tweet https://twitter.com/RailfutureNetws/status/1592284273041895424?t=tGXJulPW2CZD-I5Ybw8tTQ&s=19 1668497795 A thread showing photos of the route...

www.railforums.co.uk

Does the Portishead scheme include the reinstatement of the Down Relief from Bristol TM to Parson Street?

 

[Brissle Girl]

Does the Portishead scheme include the reinstatement of the Down Relief from Bristol TM to Parson Street?

If they did then it would make sense for it to become the main route for through traffic and aligned accordingly, so trains waiting to enter the branch don’t hold up main line services.

 

[Annetts key]

Does the Portishead scheme include the reinstatement of the Down Relief from Bristol TM to Parson Street?

No, not at this stage.

The reinstatement of the Down Relief is on Network Rail's wish list, but it would require separate funding...

 

[Ashley Hill]

No, not at this stage.

The reinstatement of the Down Relief is on Network Rail's wish list, but it would require separate funding...

Shame,even now it would be a bonus let alone with the additional Portishead services.

 

[Brissle Girl]

Shame,even now it would be a bonus let alone with the additional Portishead services.

You could add to that “nice to have” a short section of double track from Worle Jn towards Weston so that during times of disruption trains headed towards Weston can wait on the branch and not block the main line.

It was mooted around a decade ago but then dropped as not cost justifiable.

 

[Annetts key]

You could add to that “nice to have” a short section of double track from Worle Jn towards Weston so that during times of disruption trains headed towards Weston can wait on the branch and not block the main line.

It was mooted around a decade ago but then dropped as not cost justifiable.

Uphill Jcn to Worle Jcn via WsM redoubling is on the same Network Rail wish list.

As always, until some money appears from somewhere, they will remain in the wish list.

 

[Ashley Hill]

Uphill Jcn to Worle Jcn via WsM redoubling is on the same Network Rail wish list.

As always, until some money appears from somewhere, they will remain in the wish list.

And of course it will require a rebuild of Weston Milton requiring extra cash.

 

[-Colly405-]

And of course it will require a rebuild of Weston Milton requiring extra cash.

Including reclaiming the down platform slabs from Lympstone Commando?

 

[Ashley Hill]

Including reclaiming the down platform slabs from Lympstone Commando?

Indeed,but the upside platform was also moved outwards to meet the centralised track.

 

[MarkyT]

And of course it will require a rebuild of Weston Milton requiring extra cash.

Indeed,but the upside platform was also moved outwards to meet the centralised track.

Suppose all Weston Milton trains were to start and terminate at Weston Super Mare. In that case, a single platform might suffice at Weston Milton with a crossover to access it on the Bristol side of the station and a means for up trains to weave around such a movement with a section of bi-di on the down line. The platform would need to be shifted over to make room for double track, but the expense of an additional platform and its access would be avoided.

For example:

 

[Ashley Hill]

I suspect an additional platform would be cheaper than a crossover and its associated signalling. Anyhow, I imagine its probably cheaper to demolish the existing platform and build new.

 

[zwk500]

Suppose all Weston Milton trains were to start and terminate at Weston Super Mare. In that case, a single platform might suffice at Weston Milton with a crossover to access it on the Bristol side of the station and a means for up trains to weave around such a movement with a section of bi-di on the down line. The platform would need to be shifted over to make room for double track, but the expense of an additional platform and its access would be avoided.

That layout, while very nice, does seem a bit of a disproportionate response to the problem. Particularly the maintenance liability and the performance risk of having to cross trains over regularly at Weston Milton.

A GSV of the station (https://maps.app.goo.gl/Zpx3xzT95iwUwZdGA) suggests there's plenty of space for the second platform without needing to touch the existing station, although the track has been slued out near to the middle of the formation so there's two bridges that are likely to need reconstruction if the line was left where it was.

 

[Topological]

Without really understanding the geography of the area, would it not be sufficient to build the junction element and be back to single track between Weston Milton and Weston-Super-Mare?

Isn't the primary issue the single lead junction off the main line?

Still lost track of what that has to do with Portishead.

 

[Ashley Hill]

That layout, while very nice, does seem a bit of a disproportionate response to the problem. Particularly the maintenance liability and the performance risk of having to cross trains over regularly at Weston Milton.

A GSV of the station (https://maps.app.goo.gl/Zpx3xzT95iwUwZdGA) suggests there's plenty of space for the second platform without needing to touch the existing station, although the track has been slued out near to the middle of the formation so there's two bridges that are likely to need reconstruction if the line was left where it was.

Surely easier and cheaper to rebuild the platforms than bridges. There really isn`t room by the station bridge to have two tracks without moving/rebuilding the upside platform.

 

[Brissle Girl]

Without really understanding the geography of the area, would it not be sufficient to build the junction element and be back to single track between Weston Milton and Weston-Super-Mare?

Isn't the primary issue the single lead junction off the main line?

Still lost track of what that has to do with Portishead.

Yes, apart from reducing the length of the single line section, enabling trains heading to Weston to wait clear of the main line would prevent knock on delays to main line services.

 

[MarkyT]

That layout, while very nice, does seem a bit of a disproportionate response to the problem. Particularly the maintenance liability and the performance risk of having to cross trains over regularly at Weston Milton.

A GSV of the station (https://maps.app.goo.gl/Zpx3xzT95iwUwZdGA) suggests there's plenty of space for the second platform without needing to touch the existing station, although the track has been slued out near to the middle of the formation so there's two bridges that are likely to need reconstruction if the line was left where it was.

A second much simpler scheme not doubling the main line junction but effectively lengthening the double track section on the Weston loop by about 2km. Only one new turnout is required just east of Weston Milton. All junction track at Weston SM is existing. The siding turnout is reused for the additional line connection with both tracks slewed over going East so the siding merges into the current single line alignment within its length while a new track is constructed to the south of the existing for the section through to Weston Milton. The siding at Weston SM is lost in this scheme, but the extra bay platform may render it unnecessary.

A double ladder-style junction at Worle would be impossible without acquiring land on one side or the other and there's a narrow bridge nearby that would probably need rebuilding. That's why I initially showed a standard double junction with a diamond. A fixed or (god forbid) a switched diamond on such a busy high-speed stretch would probably be undesirable, so I decided to retain the single lead configuration, probably with a higher turnout speed than any double junction design on the site could achieve in both directions.

I agree it might be better to replace the road bridge near Weston Milton and thus avoid rebuilding the existing platform, whether or not an extra platform was added. Electrification clearances could also be specified. With the current single track in the middle of the former 2-track arch lower speed contact wire and catenary might fit beneath the existing span without modification.

 

[Wilts Wanderer]

That layout at Weston SM would not be appreciated in the peaks when trains in both directions call at Weston Milton and cross at Weston SM. You need both through platforms to be able to access Weston Milton for it to be practical.

 

[MarkyT]

Another refinement for the price of one more turnout would be a right turn lane

That layout at Weston SM would not be appreciated in the peaks when trains in both directions call at Weston Milton and cross at Weston SM. You need both through platforms to be able to access Weston Milton for it to be practical.

Noted thank you. I have added another crossover at Weston SM east throat to cater for your moves, and I've shifted the down homes east to be overlap clear for maximum flexibility:

Couldn't help noticing for down movements from Worle the spacing to the next signal approaching Weston SM is horrendously overbraked at something like 300% of braking distance at the branch speed of 60mph, and that's on the all trains graph. For an App. C train with 9% braking, the spacing is around 6x the braking distance. It's not supposed to exceed 150% normally! That's why I added the distant signals on the Weston Milton section.

 

[Sly Old Fox]

You won’t get double track under the bridge at Weston Milton without rejigging the platform.

 

[MarkyT]

You won’t get double track under the bridge at Weston Milton without rejigging the platform.

Or you could rebuild the road overbridge(s) as necessary.

 

[Irascible]

Or you could rebuild the road overbridge(s) as necessary.

Presumably that'd slew the newly replaced second line over - is that going to put it/presumably the slewed cess out of railway boundaries? would that add a bunch of red tape?

Also begs the question if rebuilding a bridge is less than rebuilding a station...

 

[Topological]

Is the situation at Worle really that bad? Looking at the Google Satellite view it looks like the double track formation from Weston is still there. To a lay-person it looks like a second line could be laid parallel to the existing on the south side and then curve into the mainline at the same angle as the existing.

Am I missing something about the design of junctions that prohibits the addition of a second track on the junction?

Even if it remained single lead and then immediately had a turnout for a loop then that would allow passing without the train bound for Weston needing to remain on the main line.

 

[TheLastMinute]

My understanding is that redoubling the loop will require the replacement of both bridges either side of Weston Milton anyway due to the track bed being raised over the years . That's actually no bad thing as both of them are narrow one-way strutures that were once country lanes but now form a significant link in a large town. The original plan Somerset Avenue construction plan fromt the 80s had that both of these bridges would be replaced by a new single bridge just to the west of Weston Milton. The land between Hutton Moor Roundabout and Locking Road is is still clearly visable on Google Maps Satelite view.

The bridge at Worle Junc was mentioned upthread as also maybe needing rebuilding to give more room for a ladder junction. This bridge was closed to motor vechiles about 15 years ago as it was considered to weak so could be replaced by a much smaller design.

Bringing the Down bay back into use at Weston-super-Mare I think would help significantly, particilarly as there is now a Paddington terminator that waits in the station for 30 of every 120 minutes. The bay would be used for Severn Beach terminator freeing up a through platform.

Something else that would help performance is extending the platforms at Nailsea & Backwell, Yatton, Worle and Highbridge & Burnham to at least coach lenghhs. At present, most of thses platforms are 4 coaches, meaning that often only 2 standard class coaches of an IET are platformed causing queues to get on. Extending would also help when it was 2 x 5 car IETs as both sets would be useable.

 

[MarkyT]

Is the situation at Worle really that bad? Looking at the Google Satellite view it looks like the double track formation from Weston is still there. To a lay-person it looks like a second line could be laid parallel to the existing on the south side and then curve into the mainline at the same angle as the existing.

Am I missing something about the design of junctions that prohibits the addition of a second track on the junction?

Even if it remained single lead and then immediately had a turnout for a loop then that would allow passing without the train bound for Weston needing to remain on the main line.

It might be possible to put in a parallel turnout to that existing at Worle junction leading to a diamond crossing over the up main. A fixed diamond would be better for reliability than a switched diamond, which are usually considered a failure and maintenance headache. I don't know if a fixed diamond crossing would fit or be suitable given the speed and traffic characteristics. A diamond of either type would be hammered by the fast and heavy traffic on the up main so might be considered undesirable, compared to a series of turnouts. Ladder type double junctions are usually longer than diamond types, which can make retrofitting one in the space available at a former diamond junction difficult. Here, a parallel ladder might be squeezed in with some weird geometry and the new line cutting across the allotments and the wooded area in the junction 'V', noting in the trees there's a large electricity pylon for a high voltage supply route parallelling the railway, which might complicate matters! Within those confines, it might not be possible to match the 40mph speed of the existing junction turnout for the new pointwork, which could mean a lower junction speed for a down train turning right into Weston SM than for an up train leaving town.

 

[Topological]

It might be possible to put in a parallel turnout to that existing at Worle junction leading to a diamond crossing over the up main. A fixed diamond would be better for reliability than a switched diamond, which are usually considered a failure and maintenance headache. I don't know if a fixed diamond crossing would fit or be suitable given the speed and traffic characteristics. A diamond of either type would be hammered by the fast and heavy traffic on the up main so might be considered undesirable, compared to a series of turnouts. Ladder type double junctions are usually longer than diamond types, which can make retrofitting one in the space available at a former diamond junction difficult. Here, a parallel ladder might be squeezed in with some weird geometry and the new line cutting across the allotments and the wooded area in the junction 'V', noting in the trees there's a large electricity pylon for a high voltage supply route parallelling the railway, which might complicate matters! Within those confines, it might not be possible to match the 40mph speed of the existing junction turnout for the new pointwork, which could mean a lower junction speed for a down train turning right into Weston SM than for an up train leaving town.

View attachment 157348

Thank you for the detailed explanation.

This then moves towards a loop which starts just after the Weston line leaves the main line. Such would still allow the Weston bound train to get off the main line and pass a Bristol bound train coming out of Weston could then be held whilst the Weston bound train entered the loop.

It does seem like some improvement would be possible, but there is a constant trade-off of cost v benefit. It just seems sad that the present situation involves the Weston bound train sitting on the main line.

 

[Irascible]

If the purpose of the loop is just to cross over trains in & out of WSM, can't it go the other side of Weston Milton? it'd add 30s or so ( at a guess ) but it'd also save all this awkwardness.

 

[MarkyT]

If the purpose of the loop is just to cross over trains in & out of WSM, can't it go the other side of Weston Milton? it'd add 30s or so ( at a guess ) but it'd also save all this awkwardness.

Are you saying move the single to double connection west of Weston Milton or to double between Worle Junction and Weston Milton? Either or both is possible but the platform would still be on the solitary single line adding to the occupancy time for every train that stopped.

Other possibilities spring to mind if the main lines could be slewed over an interval to the south through the junction area. It would have to be over a significant length to avoid affecting through speed. Then a conventional double ladder junction might be possible without affecting any of the residential properties on the north side of the line. The mains would have to regain their alignment between the junction and Worle station platfroms.

 

[Ashley Hill]

The platform at Weston Milton is a bolt together concrete affair therefore easily moveable. The upside has already been moved once and the downside moved to Devon and by no means the only example of that type to be moved to a new home. moving the existing platform to its origonal location should not be difficult.

 

[Irascible]

Are you saying move the single to double connection west of Weston Milton or to double between Worle Junction and Weston Milton? Either or both is possible but the platform would still be on the solitary single line adding to the occupancy time for every train that stopped.

In my head the station was a bit further east for some reason, either would work I guess. However there doesn't seem to be much stopping the whole station being slewed - a few parking spaces by the looks of it - as above, so that's by far the best idea.

 

[sleepy_hollow]

....

Bringing the Down bay back into use at Weston-super-Mare I think would help significantly, particilarly as there is now a Paddington terminator that waits in the station for 30 of every 120 minutes. The bay would be used for Severn Beach terminator freeing up a through platform.
...

And for a typical example of the operating problems with three trains in the area close to the hour see my trip report: https://www.railforums.co.uk/thread...ton-yat-open-jaw-congestion-at-weston.266921/. This risk presumably arises every two hours.

However, it does seem that using the bay or redoubling would not have any incidence on the looping of Severn Beach trains before Yatton to allow late running northbound XC to pass.