Scotrail Class 385 Discussion

[Altnabreac]

You don't have to lengthen every platform. SDO means that you'll probably just lose the rear door of the last carriage at a standard station. So long as the core infrastructure doesn't present major barriers there's not really a reason to restrict to 20m carriages, which are becoming less standard now that the Southern Region no longer dictates EMU design.

I agree that 23m carriages are the future for Scotrail. Now the 385s have followed the 380s it seems likely future ScotRail EMU orders will follow this pattern.

Equally however platform lengthening from 6x20 to 6x23 is a bit pointless and expensive. I think we’ll see a combination of SDO and a move towards more 4 and 8 carriage trains with the busier stations seeing lengthening to platforms of 190m or so.

Until services are running full at 8 x 23m units it is difficult to justify increasing frequencies via expensive infrastructure interventions.

 

[CM]

I agree that 23m carriages are the future for Scotrail. Now the 385s have followed the 380s it seems likely future ScotRail EMU orders will follow this pattern.

Equally however platform lengthening from 6x20 to 6x23 is a bit pointless and expensive. I think we’ll see a combination of SDO and a move towards more 4 and 8 carriage trains with the busier stations seeing lengthening to platforms of 190m or so.

Until services are running full at 8 x 23m units it is difficult to justify increasing frequencies via expensive infrastructure interventions.

It'll never happen, have you ever actually used the North Clyde line? It would be utterly stupid and pointless acquring trains which would not fit into about 90% of the platforms. Off the top of my head, stations I know of that could currently accomodate 6x 23m trains are Helensburgh, Clydebank, Dumbarton Central and Possibly the through platforms at Dalmuir. Acquiring trains which could only fully fit into quite litterally a handfull of of stations is just silly.

 

[Rick1984]

I hadn't thought of the length. Wonder if the AT100 could be made to standard suitable to replace all suburban stock, maybe 334's for the longer stuff

 

[Altnabreac]

It'll never happen, have you ever actually used the North Clyde line? It would be utterly stupid and pointless acquring trains which would not fit into about 90% of the platforms. Off the top of my head, stations I know of that could currently accomodate 6x 23m trains are Helensburgh, Clydebank, Dumbarton Central and Possibly the through platforms at Dalmuir. Acquiring trains which could only fully fit into quite litterally a handfull of of stations is just silly.

Is it easier to extend platforms and use SDO or to fit more services through Partick?

Once all current services are run using 6 x 20m EMUs this becomes the equation if demand continues to grow.

I agree the benefit of going to 6 x 23m is marginal. Going to 8 x 23m is a step change though and on the North Clyde lines likely to be better value than trying to four track Partick - Hyndland. Probably ten years away from that being needed though.

 

[adrock1976]

I thought 700s , 710s or 345s would be more suited .

Pushing the boat out a bit here, if Glasgow City Council (and other neighbouring councils), plus Strathclyde PTE grabbed the bull by the horns, they could bring back trams with the conversion of the Cathcart route being part of a second phase of a tram project.

They could even get the people from Manchester to help, as they are the experts in converting existing and former railway lines to tram operation.

 

[NotATrainspott]

It'll never happen, have you ever actually used the North Clyde line? It would be utterly stupid and pointless acquring trains which would not fit into about 90% of the platforms. Off the top of my head, stations I know of that could currently accomodate 6x 23m trains are Helensburgh, Clydebank, Dumbarton Central and Possibly the through platforms at Dalmuir. Acquiring trains which could only fully fit into quite litterally a handfull of of stations is just silly.

Whether or not SDO is suitable at a location will depend on a variety of factors. One of them is the degree of passenger churn. The more people expected to get on and off at a station, the less viable SDO is as a concept. SDO wouldn't for instance, work well at termini or major interchange stations as large proportions of passengers are expected to board or alight. Thankfully, the platforms at Queen Street LL are already known to be 6x23m, and the Charing Cross platforms appear to be physically long enough albeit out-of-use at the M8 end. All new platforms built for the Airdire-Bathgate project are also capable of 6x23m, so that's the entire eastern end of the line covered. There are various platforms along the route which could be fairly trivially extended by 20m or so - something to remember is that modern platforms are square to the end, rather than tapered, so a big chunk of that 20m could actually be done without increasing the real length of the platform structure.

If a new ScotRail operator suggests the use of 6x23m trains on the line, they'll go through a feasibility process first and consider any costs as part of the new train fleet. If the cost of enabling a 6x23m fleet is higher than the benefit of one, then it won't happen.

 

[mde]

Pushing the boat out a bit here, if Glasgow City Council (and other neighbouring councils), plus Strathclyde PTE grabbed the bull by the horns, they could bring back trams with the conversion of the Cathcart route being part of a second phase of a tram project.

They could even get the people from Manchester to help, as they are the experts in converting existing and former railway lines to tram operation.

What would be the point in converting the circle to a tram line?

 

[CM]

Whether or not SDO is suitable at a location will depend on a variety of factors. One of them is the degree of passenger churn. The more people expected to get on and off at a station, the less viable SDO is as a concept. SDO wouldn't for instance, work well at termini or major interchange stations as large proportions of passengers are expected to board or alight. Thankfully, the platforms at Queen Street LL are already known to be 6x23m, and the Charing Cross platforms appear to be physically long enough albeit out-of-use at the M8 end. All new platforms built for the Airdire-Bathgate project are also capable of 6x23m, so that's the entire eastern end of the line covered. There are various platforms along the route which could be fairly trivially extended by 20m or so - something to remember is that modern platforms are square to the end, rather than tapered, so a big chunk of that 20m could actually be done without increasing the real length of the platform structure.

If a new ScotRail operator suggests the use of 6x23m trains on the line, they'll go through a feasibility process first and consider any costs as part of the new train fleet. If the cost of enabling a 6x23m fleet is higher than the benefit of one, then it won't happen.

It's not the entire eastern end of the line, High Street, Bellgrove, Carntyne, Shettleston, Garrowhill, Easterhouse, Blairhill, Coatbridge Sunnyside, Coatdyke and Airdrie. These stations must also be a factor in wether or not 6x 23m trains would be feasable, unless of course you plan on just abandoning them altogether? Apart from the Edinburgh to Milngavie/Helensburgh service just about 99% of service call at all stations along these routes,. Then there's also the fact that the 334s do not just work the A2B services alone, they also regularly find there way onto other services including Argyle Line services alongside the 318s and 320s. So if you replace the 318s, 320s and 334s with 6x 23m trains, you have a hell of a lot of stations that would need lengthening and there is quite a few that without serious re-construction work or even completley moving the station to a different location, could not be extended to fit 6x 23m trains.

 

[route101]

Have the 385 times changed? Was xx15 past the hour every 2 hours . The 1800 Edinburgh to Queen st was a 385

 

[youngac]

Have the 385 times changed? Was xx15 past the hour every 2 hours . The 1800 Edinburgh to Queen st was a 385

I think it runs xx00 services only on Saturdays. It goes back to the usual xx15 services on Mondays - Fridays.

 

[Sirius]

It's not the entire eastern end of the line, High Street, Bellgrove, Carntyne, Shettleston, Garrowhill, Easterhouse, Blairhill, Coatbridge Sunnyside, Coatdyke and Airdrie. These stations must also be a factor in wether or not 6x 23m trains would be feasable, unless of course you plan on just abandoning them altogether? Apart from the Edinburgh to Milngavie/Helensburgh service just about 99% of service call at all stations along these routes,. Then there's also the fact that the 334s do not just work the A2B services alone, they also regularly find there way onto other services including Argyle Line services alongside the 318s and 320s. So if you replace the 318s, 320s and 334s with 6x 23m trains, you have a hell of a lot of stations that would need lengthening and there is quite a few that without serious re-construction work or even completley moving the station to a different location, could not be extended to fit 6x 23m trains.

I suppose the plan could be to educate passengers which carriages to use. That said given the loading I see on the line locals are too lasy to walk 50m for a seat.

 

[NotATrainspott]

It's not the entire eastern end of the line, High Street, Bellgrove, Carntyne, Shettleston, Garrowhill, Easterhouse, Blairhill, Coatbridge Sunnyside, Coatdyke and Airdrie. These stations must also be a factor in wether or not 6x 23m trains would be feasable, unless of course you plan on just abandoning them altogether? Apart from the Edinburgh to Milngavie/Helensburgh service just about 99% of service call at all stations along these routes,. Then there's also the fact that the 334s do not just work the A2B services alone, they also regularly find there way onto other services including Argyle Line services alongside the 318s and 320s. So if you replace the 318s, 320s and 334s with 6x 23m trains, you have a hell of a lot of stations that would need lengthening and there is quite a few that without serious re-construction work or even completley moving the station to a different location, could not be extended to fit 6x 23m trains.

I'm not proposing we stop calling at those stations. A proposal to run 6x23m trains would need to look at every platform and siding along the route to see what was possible. As I was saying, at many suburban platforms SDO will be a perfectly suitable compromise. It would only be one door off of the platform, which would be fine for any station with a low expected churn rate. Junction and signal positioning is normally more of a challenge, as SDO can't make long trains be shorter.

Let's do a quick check of platform length possibilities using Google Maps' measurement tool:

Drumgelloch - Waverley are all new-build and deliberately capable of 6x23m
Airdrie: all platforms ~150m long
Coatdyke: currently 120m, trivial extension/SDO
Coatbridge Sunnyside: currently ~140m long
Blairhill: 120m long, straightforward extension/SDO
Easterhouse: 120m long, trivial extension/SDO
Garrowhill: 120m long, straightforward extension/SDO
Shettleston: 120m long, straightforward extension/SDO
Carntyne: 120m long, straightforward extension/SDO
-
Springburn: ~130m long, will be served by 6x23m EGIP services. Recent junction work complicates eastern extension of through platforms.
Barnhill: ~130m long, SDO likely
Alexandra Parade: ~120m long, SDO likely
Duke Street: ~140m long
-
Bellgrove: 130m long, non-trivial extension due to road bridges/junction but possibly doable as part of wider redevelopment
High Street: ~150m long, extreme ends are incredibly narrow so may require redevelopment - there are already City Deal plans to do something here so it could tie in
Queen Street LL: 6x23m operation known from summer 2016 diversions
Charing Cross: extra length available at western end of platforms under M8 bridge structure
Partick: 120m long, extension non-trivial but likely possible towards Dumbarton Road. Major interchange station so SDO not feasible.
Hyndland: 120m long, extension possible to north-west. SDO not ideal.
-
Anniesland: 130m long, northwards extension trivial (new junction towards Maryhill well clear of platform ends)
Westerton: 120m long, eastward extension seems possible. Hard constraint on western end due to junction.
-
Bearsden: ~120m long, trivial extension southwards
Hillfoot: ~130m long, extension straightforward
Milngavie: ~130m long, extension straightforward
-
Drumchapel: 120m long, unused platform length available at eastern end
Drumry: ~130m long, trivial extension/SDO
Singer: ~130m long, unused platform length available at western end.
-
Jordanhill: ~130m long, extension possible but SDO more likely
Scotstounhill: ~140m long,
Garscadden: ~120m long, SDO likely
Yoker: ~140m long
Clydebank: ~150m long
-
Dalmuir: ~120m long, P3/4/5 possibly extendable westwards. P1/2 extension would likely require re-alignment of the bay platform to preserve width. Already used by 6x23m WHL trains but requiring local-door operation by guard, so there'd be an immediate benefit.
Kilpatrick: ~120m long, very likely candidate for SDO due to relatively low usage and constraint of Erskine Bridge at east and underbridge at west end.
Bowling: ~120m, likely SDO candidate given closure of level crossing to west, eastward extension complicated by interface with harbour
Dumbarton East: ~130m, straightforward extension/SDO
Dumbarton Central: ~180m, already served by 6x23m WHL trains with full door access
Dalreoch: ~130m, hard constraint at either end so SDO likely
-
Cardross: ~120m, trivial eastward extension/SDO, westward constrained by level crossing. Eastbound platform already 150m long so level crossing not an SDO problem.
Craigendoran: unable to determine, but a rationalised single line on a former large station site so likely easy
Helensburgh Central: known to take 9x20m for stabling.
-
Renton: ~120m, trivial extension/SDO
Alexandria: ~120m, difficult extension but SDO likely
Balloch: ~130m, southward extension should be straightforward. SDO complicated by need for turn-around procedure.

Obviously this was a very simplistic desk exercise using open-source information. However, it suggests it'd be generally easy to run 6x23m on the North Clyde line. A ScotRail operator would need to do a much more thorough job but there don't appear to be glaring issues. The biggest thing I've found would be the adjustment of P1/2 at Dalmuir.

 

[Lucaslikes]

I think it runs xx00 services only on Saturdays. It goes back to the usual xx15 services on Mondays - Fridays.

You wouldn't happen to know when they've been running on a Sunday?

 

[Sirius]

I believe until now they have not ran on Sundays. A day off for Hitachi engineers apparently.

 

[laseandre]

<SNIP>
Dalmuir: ~120m long, P3/4/5 possibly extendable westwards. P1/2 extension would likely require re-alignment of the bay platform to preserve width. Already used by 6x23m WHL trains but requiring local-door operation by guard, so there'd be an immediate benefit.
</SNIP>

In my experience of riding 6-car 156s through Dalmuir, the two platforms used (1/2) are plenty long enough to hold them, and no special procedure is required.

 

[scotraildriver]

In my experience of riding 6-car 156s through Dalmuir, the two platforms used (1/2) are plenty long enough to hold them, and no special procedure is required.

They are NOT long enough. 6 car WHL services have to use 1 door operation at Dalmuir and it causes some delays. The train cast just fit southbound if the driver stops closer to the signal than permitted, in reality most do this though.

 

[CM]

I'm not proposing we stop calling at those stations. A proposal to run 6x23m trains would need to look at every platform and siding along the route to see what was possible. As I was saying, at many suburban platforms SDO will be a perfectly suitable compromise. It would only be one door off of the platform, which would be fine for any station with a low expected churn rate. Junction and signal positioning is normally more of a challenge, as SDO can't make long trains be shorter.

Let's do a quick check of platform length possibilities using Google Maps' measurement tool:

Drumgelloch - Waverley are all new-build and deliberately capable of 6x23m
Airdrie: all platforms ~150m long
Coatdyke: currently 120m, trivial extension/SDO
Coatbridge Sunnyside: currently ~140m long
Blairhill: 120m long, straightforward extension/SDO
Easterhouse: 120m long, trivial extension/SDO
Garrowhill: 120m long, straightforward extension/SDO
Shettleston: 120m long, straightforward extension/SDO
Carntyne: 120m long, straightforward extension/SDO
-
Springburn: ~130m long, will be served by 6x23m EGIP services. Recent junction work complicates eastern extension of through platforms.
Barnhill: ~130m long, SDO likely
Alexandra Parade: ~120m long, SDO likely
Duke Street: ~140m long
-
Bellgrove: 130m long, non-trivial extension due to road bridges/junction but possibly doable as part of wider redevelopment
High Street: ~150m long, extreme ends are incredibly narrow so may require redevelopment - there are already City Deal plans to do something here so it could tie in
Queen Street LL: 6x23m operation known from summer 2016 diversions
Charing Cross: extra length available at western end of platforms under M8 bridge structure
Partick: 120m long, extension non-trivial but likely possible towards Dumbarton Road. Major interchange station so SDO not feasible.
Hyndland: 120m long, extension possible to north-west. SDO not ideal.
-
Anniesland: 130m long, northwards extension trivial (new junction towards Maryhill well clear of platform ends)
Westerton: 120m long, eastward extension seems possible. Hard constraint on western end due to junction.
-
Bearsden: ~120m long, trivial extension southwards
Hillfoot: ~130m long, extension straightforward
Milngavie: ~130m long, extension straightforward
-
Drumchapel: 120m long, unused platform length available at eastern end
Drumry: ~130m long, trivial extension/SDO
Singer: ~130m long, unused platform length available at western end.
-
Jordanhill: ~130m long, extension possible but SDO more likely
Scotstounhill: ~140m long,
Garscadden: ~120m long, SDO likely
Yoker: ~140m long
Clydebank: ~150m long
-
Dalmuir: ~120m long, P3/4/5 possibly extendable westwards. P1/2 extension would likely require re-alignment of the bay platform to preserve width. Already used by 6x23m WHL trains but requiring local-door operation by guard, so there'd be an immediate benefit.
Kilpatrick: ~120m long, very likely candidate for SDO due to relatively low usage and constraint of Erskine Bridge at east and underbridge at west end.
Bowling: ~120m, likely SDO candidate given closure of level crossing to west, eastward extension complicated by interface with harbour
Dumbarton East: ~130m, straightforward extension/SDO
Dumbarton Central: ~180m, already served by 6x23m WHL trains with full door access
Dalreoch: ~130m, hard constraint at either end so SDO likely
-
Cardross: ~120m, trivial eastward extension/SDO, westward constrained by level crossing. Eastbound platform already 150m long so level crossing not an SDO problem.
Craigendoran: unable to determine, but a rationalised single line on a former large station site so likely easy
Helensburgh Central: known to take 9x20m for stabling.
-
Renton: ~120m, trivial extension/SDO
Alexandria: ~120m, difficult extension but SDO likely
Balloch: ~130m, southward extension should be straightforward. SDO complicated by need for turn-around procedure.

Obviously this was a very simplistic desk exercise using open-source information. However, it suggests it'd be generally easy to run 6x23m on the North Clyde line. A ScotRail operator would need to do a much more thorough job but there don't appear to be glaring issues. The biggest thing I've found would be the adjustment of P1/2 at Dalmuir.

SOME platforms could be easily extended yes, I agree. But you really have to look at the bigger picture here, you've only factored in the North Clyde line platforms. You also need to factor in platforms on the Argyle line as apart from Helensburgh/Milngavie to Edinburgh services which are STRICTLY operated by the 334s, the rest of the services can and are operated by a mix of 318, 320 and 334.

You say Dalmuir is the biggest issue, it isn't. Extending Partick for example would be ridiculously expensive as you have a road bridge at either end of the platforms which would obviously need replaced with wider bridges to accomodate extra platform length.

Take it from someone who actually LIVES and USES the line on a regular basis, 6x 23m will not work as it would be prohibitively expensive to extend every platform.

 

[Carntyne]

If you were looking to add capacity to the route, you would operate more 6 coach services, which is what the additional 5x320 units are coming for.

Next up, fixed formation 6 car (no intermediate cab ends) instead? Through gangways?

 

[DanNCL]

In my experience of riding 6-car 156s through Dalmuir, the two platforms used (1/2) are plenty long enough to hold them, and no special procedure is required.

They are NOT long enough. 6 car WHL services have to use 1 door operation at Dalmuir and it causes some delays. The train cast just fit southbound if the driver stops closer to the signal than permitted, in reality most do this though.

The 6 car 156 formations do stop at Dalmuir without any sort of special procedure, all doors open. I've seen this for myself, the platform is definitely long enough for them. 6x 23m does fit in the platforms used by WHL services at Dalmuir.

 

[scotraildriver]

I must have imagined doing 1 door operation at Dalmuir for the last 13 years then.

 

[Altnabreac]

The 6 car 156 formations do stop at Dalmuir without any sort of special procedure, all doors open. I've seen this for myself, the platform is definitely long enough for them. 6x 23m does fit in the platforms used by WHL services at Dalmuir.

I must have imagined doing 1 door operation at Dalmuir for the last 13 years then.

I love it on this forum when people know better than the folk who actually drive the trains each day...

 

[InOban]

What would be the point in converting the circle to a tram line?

Because a tram would extend into Castlemilk and other areas of high-density housing, as well as distributing passengers to a wider area of Glasgow.

 

[mde]

Because a tram would extend into Castlemilk and other areas of high-density housing, as well as distributing passengers to a wider area of Glasgow.

Is there demand for it? That area as a specific example has a 'good' bus service which covers the key commuter areas that would be covered by the current circle line. In all honesty, it feels like a solution looking for a problem.

If Glasgow can justify it there is probably more interest in using some of the 'City Deal' funding for the airport rail link… a 385 on that route with sufficient luggage storage would probably be well received by passengers.

 

[JumpinTrainz]

I honestly think as the population grows, Scotland needs to look at its infrastructure especially in major cities like Glasgow and Edinburgh. An extension of Partick is definitely something to look at. It’s an interchange station for the North Clyde and Argyle Line and is an extremely busy station. Yes a lot of these expansions would cost a lot of money but look at the works which went into the M8/M74. It’s not the exact same thing but capacity has meant for massive expansion. It cost lots of money and caused lots of upheaval but if it needs to happen then it needs to happen. We are not living in the 20th century anymore. Population is growing and so must transport links.

When looking at the bigger picture it’s baffling to think the main train connection from Glasgow to Edinburgh has just gone electric in 2018!!

 

[NotATrainspott]

What would be the point in converting the circle to a tram line?

The idea to convert the Cathcart Circle to a metro is not new. A metro line, explicitly including conversion of existing heavy rail routes, is presented as an option in the STPR to address Glasgow terminus capacity problems. I'm an advocate, but I know that others have concerns about the practicality of such a conversion. The primary benefit is that conversion would make it possible to ramp up frequencies at all times of the day, which is the most important part of journey times for a line so relatively short and self-contained. Running 20tph from Pollokshields into the city centre isn't really practical with heavy rail technology.

SOME platforms could be easily extended yes, I agree. But you really have to look at the bigger picture here, you've only factored in the North Clyde line platforms. You also need to factor in platforms on the Argyle line as apart from Helensburgh/Milngavie to Edinburgh services which are STRICTLY operated by the 334s, the rest of the services can and are operated by a mix of 318, 320 and 334.

You say Dalmuir is the biggest issue, it isn't. Extending Partick for example would be ridiculously expensive as you have a road bridge at either end of the platforms which would obviously need replaced with wider bridges to accomodate extra platform length.

Take it from someone who actually LIVES and USES the line on a regular basis, 6x 23m will not work as it would be prohibitively expensive to extend every platform.

It wouldn't be the end of the world if the Argyle line continued to use 6x20m trains. My expectation is that the 318/320 replacement will be 23m trains, and the 334s will live out the rest of their days on the Argyle line. It seems like the Argyle line is going to end up serving shorter, more urban journeys remaining within the contiguous built-up area of Glasgow. The North Clyde, on the other hand, sees 2-hour runs from coast to coast. Even after EGIP it'll remain a competitive option for commuting between the wider urban areas of Glasgow and Edinburgh. That means it might well be worthwhile to have a more metro-style rolling stock which wouldn't ever interwork through to Edinburgh. I've seen vaguely crayonista ideas about separating the Argyle line away from the NR network and running it as a proper subway line but I don't think this is likely to happen, given that it wouldn't solve the Hyndland bottleneck.

There is a gap of at least 20m between the Dumbarton Road bridge and the northern end of the platforms at Partick. That's sufficient for 6x23m, requiring only a short extension on top of the existing railway viaduct. Extending beyond that is where I think the value proposition fails - unlike Altnabraec I don't think the solution to capacity constraints is to go for widespread 8x23m running.

Don't be so presumptive about who has experience of a line. In any case, familiarity doesn't necessarily mean you will know what's actually possible, rather than what happens today. Sometimes you need a fresh pair of eyes to look at a situation to see what could be improved.

 

[InOban]

1. Areas such as Castlemilk may have high frequency bus services (so, incidentally does East Kilbride) but they suffer from unpredictable journey times because of traffic congestion.

2. Where Glasgow has failed miserably, and I don't think it's even proposed for the City Deal, is in provision of Park and Ride facilities, such as Edinburgh has. Drumry, for instance, is just the other side of the A82 from a large shopping centre (B&Q, furniture, Sainsbury's, a lot of takeaways) whose car park is generally quiet during the day. Both sides have pedestrian access to the dual carriageway, just no safe way to cross.

 

[route101]

1. Areas such as Castlemilk may have high frequency bus services (so, incidentally does East Kilbride) but they suffer from unpredictable journey times because of traffic congestion.

2. Where Glasgow has failed miserably, and I don't think it's even proposed for the City Deal, is in provision of Park and Ride facilities, such as Edinburgh has. Drumry, for instance, is just the other side of the A82 from a large shopping centre (B&Q, furniture, Sainsbury's, a lot of takeaways) whose car park is generally quiet during the day. Both sides have pedestrian access to the dual carriageway, just no safe way to cross.

Castlemilk has 2 frequent bus services , the 75 and 5 . Few other routes too.

East Kilbride has frequent buses but services are much less reliable , the routes may be held up coming out of town and a lot of areas are not near buses nor trains.

 

[clc]

The idea to convert the Cathcart Circle to a metro is not new. A metro line, explicitly including conversion of existing heavy rail routes, is presented as an option in the STPR to address Glasgow terminus capacity problems. I'm an advocate, but I know that others have concerns about the practicality of such a conversion. The primary benefit is that conversion would make it possible to ramp up frequencies at all times of the day, which is the most important part of journey times for a line so relatively short and self-contained. Running 20tph from Pollokshields into the city centre isn't really practical with heavy rail technology.
.

Thinking long term, say 25 years from now, and assuming Network Rail’s demand forecasts are accurate, would tram train be able to provide enough capacity to meet peak time demand on the Cathcart lines? Could you feasibly run 30-40 tram trains per hour in the peak?

There’s a high risk you’d regret giving up the potential capacity which heavy rail would offer.

 

[gsnedders]

If you were looking to add capacity to the route, you would operate more 6 coach services, which is what the additional 5x320 units are coming for.

Next up, fixed formation 6 car (no intermediate cab ends) instead? Through gangways?

Yeah, I strongly suspect fixed formation 6 car trains are the future of ScotRail's 20m EMUs—we'll see the 318/320 replacement in the next franchise (how early probably mostly depending on order books at the time), and as I've said before I expect they'll also replace the 385s on the Cathcart Circle routes.

 

[sash5000]

Equally however platform lengthening from 6x20 to 6x23 is a bit pointless and expensive. I think we’ll see a combination of SDO and a move towards more 4 and 8 carriage trains with the busier stations seeing lengthening to platforms of 190m or so.

Another option might be 5x23 units. Would have more space as you only have 2 cabs not 4 and only need 1 accessible loo instead of 2 and still fit in the exisiting platforms.

The train frequency through both tunnels is very low at 6 an hour via Central and 8 an hour via Queen Street so another option would be more trains rather than longer ones, although some of these would need to terminate before the routes merge at Partick.