Ideas for cascading ScotRail DMUs following introduction of new EMU/BEMU stock

[stevieinselby]

You'd surely electrify Ashfield - Westerton on the Maryhill route to allow future BEMUs for the West Highland Line to run electric all the way to Craigendoran.

mods note - split from this thread.

ScotRail Suburban Fleet (EMU and BEMU) Market Engagement

ScotRail Trains Limited (SRT) Market Engagement Notice SRT is launching a market engagement exercise in relation to its proposed procurement for the replacement of some of its aging Diesel and Electric Multiple Units with a new fleet of Electric Multiple Units (EMUs) and Battery Electric...

www.railforums.co.uk

From Glasgow to Craigendoran Junction is just 14% of the route to Mallaig – it's another 142 miles from there on unelectrified lines, and while they aren't fast they are hilly and so could be quite demanding of a battery pack. That seems ambitious with current technology – the West Highland Line is likely to be one of the last holdouts of diesel, along with the Far North and Kyle lines. Even so, if you can deal with the distance beyond Craigendoran then you can deal with a short stretch around Maryhill. Either way, there doesn't seem to be any pressing need for that section to be electrified for half a dozen trains a day.

With the Fife circle also getting these BEMUs it will mean more DMUs scrapped or cascaded.

I don't know whether Northern or GWR will be interested in taking Scotrail's 156s as an interim measure, but I'm sure there will be plenty of happy homes awaiting any 158s or 170s that are surplus to requirements.

 

[Brubulus]

From Glasgow to Craigendoran Junction is just 14% of the route to Mallaig – it's another 142 miles from there on unelectrified lines, and while they aren't fast they are hilly and so could be quite demanding of a battery pack. That seems ambitious with current technology – the West Highland Line is likely to be one of the last holdouts of diesel, along with the Far North and Kyle lines. Even so, if you can deal with the distance beyond Craigendoran then you can deal with a short stretch around Maryhill. Either way, there doesn't seem to be any pressing need for that section to be electrified for half a dozen trains a day.

I don't know whether Northern or GWR will be interested in taking Scotrail's 156s as an interim measure, but I'm sure there will be plenty of happy homes awaiting any 158s or 170s that are surplus to requirements.

Is it actually physically impossible for a 170 to run the WHL? There will need to be a solution for that line.

 

[TrainViation]

Is it actually physically impossible for a 170 to run the WHL? There will need to be a solution for that line.

From what I remember, I think they were talking about a permanent non OHLE solution, and that being Hydrogen.

 

[Snow1964]

Is it actually physically impossible for a 170 to run the WHL? There will need to be a solution for that line.

It is about clearances due to length and size of bogies. Seen it said the clearances are too small, but no idea how many millimetres adjustment is required and how many metres of track it applies to.

More likely the 196s would come free, assuming BEMUs can take over some routes, and/or add ons to busy West Midlands network get electrified (which is lot more likely than hundreds of miles in Highlands with handful of trains each day).

196s you take it through to about year 2060, by which time some new solution, or hydrogen cells might be realistic

 

[AndrewE]

196s you take it through to about year 2060, by which time some new solution, or hydrogen cells might be realistic

Hydrogen is not going to be the answer to anything anywhere. Most likely to be better batteries in a BEMU - or something like a Motor Luggage Van or a battery loco which lives at the outer end of the electrification and couples on to assist the B/EMU and extend its range.

 

[AlastairFraser]

Hydrogen is not going to be the answer to anything anywhere. Most likely to be better batteries in a BEMU - or something like a Motor Luggage Van or a battery loco which lives at the outer end of the electrification and couples on to assist the B/EMU and extend its range.

With the prospect of floating wind turbines with directly connected electrolysis pods coming to market, Scotland may have a reliable supply of cheap renewable hydrogen that will be viable for lines like the Far North and West Highland that have no realistic prospect of electrification.

 

[BlueLeanie]

If an Ember Coach can make it from Edinburgh to Fort William, why couldn't a BEMU make it from Helensburgh(?) to Fort William?

The overall elevation is the same, the distance shorter

 

[N1]

From Glasgow to Craigendoran Junction is just 14% of the route to Mallaig – it's another 142 miles from there on unelectrified lines, and while they aren't fast they are hilly and so could be quite demanding of a battery pack. That seems ambitious with current technology – the West Highland Line is likely to be one of the last holdouts of diesel, along with the Far North and Kyle lines.

Ember can do Glasgow and Edinburgh to Fort William return on a single charge. Seems completely achievable to use BEMU to do West Highland.

== Doublepost prevention - post automatically merged: 8 Sep 2025 ==

If an Ember Coach can make it from Edinburgh to Fort William, why couldn't a BEMU make it from Helensburgh(?) to Fort William?

The overall elevation is the same, the distance shorter

Same time

 

[TheWalrus]

If possible would it make sense to get the newer DMUs (i.e. the 170s) cleared on routes currently operated by 156s so when electrification and BMU/EMUs come into play, the 170s would provide a solution until at least early 2040s?

 

[Nottingham59]

they are hilly and so could be quite demanding of a battery pack.

If it's hilly, that's all the more reason to have a battery pack to recover energy going downhill. But with 142 miles of route and always the possibility of getting snowed in for several days in winter, it needs a diesel too. So i'd say the answer to lines like WHL and Far North is a trimode with an HVO-compatible diesel.

 

[Russel]

To me, the nature of the WHL would suggest it's one of the few lines where diesel, or at least, diesel hybrid, is the only realistic option.

 

[AlastairFraser]

To me, the nature of the WHL would suggest it's one of the few lines where diesel, or at least, diesel hybrid, is the only realistic option.

Or potentially hydrogen/battery/OHLE trimodes, given that even now, there are viable renewable hydrogen projects in the Highlands and Islands region of Scotland (e.g. the Surf and Turf project in Orkney: https://www.surfnturf.org.uk/) for small-scale production.

When the last ScotRail diesels (probably the 170s) become life expired towards the end of the 2030s, the infrastructure will become significantly more advanced.

 

[BerkshireRails]

I would imagine the 153s will stay and will be paired with the 158s instead of the 156s on the West Highland Line, as the 158s will be freed up from the Fife Circle and Borders line. Electric borders frees up six sets (2tph with 3-hour round trip), probably another five on Leven (1tph with 5-hour round trip), and another three to four sets on Cowdenbeath (1tph with 3-4-hour round trip). The freed-up sets will be a mixture of 158s and 170s, with the 170s taking over existing 158s services to enable 158s to work the West Highland Line. Based on a quick look at Real Time Trains.

If the West Highland Line goes to Battery units, then I would recommend fast chargers roughly every 30-40 miles at Crianlarich, Rannoch, Fort William, Mallaig and Oban.

Crianlarich because of the long wait times due to the splitting and joining of the Oban and Mallaig portions of the train.

Rannoch, because it is around 30 miles from Crianlarich, with a waiting time due to passing trains.

Fort William is around 35 miles from Rannoch, and it is where the units sit for 5 minutes to allow the driver to change ends to continue the trip on Scotrail services, and where the Caledonian Sleeper terminates.

Mallaig, because it is the terminus of all services and is around 39 miles from Fort William.

Oban because it is the terminus of all services and is around 42 miles from Crianlarich.

 

[Russel]

I would imagine the 153s will stay and will be paired with the 158s instead of the 156s on the West Highland Line, as the 158s will be freed up from the Fife Circle and Borders line. Electric borders frees up six sets (2tph with 3-hour round trip), probably another five on Leven (1tph with 5-hour round trip), and another three to four sets on Cowdenbeath (1tph with 3-4-hour round trip). The freed-up sets will be a mixture of 158s and 170s, with the 170s taking over existing 158s services to enable 158s to work the West Highland Line. Based on a quick look at Real Time Trains.

If the West Highland Line goes to Battery units, then I would recommend fast chargers roughly every 30-40 miles at Crianlarich, Rannoch, Fort William, Mallaig and Oban.

Crianlarich because of the long wait times due to the splitting and joining of the Oban and Mallaig portions of the train.

Rannoch, because it is around 30 miles from Crianlarich, with a waiting time due to passing trains.

Fort William is around 35 miles from Rannoch, and it is where the units sit for 5 minutes to allow the driver to change ends to continue the trip on Scotrail services, and where the Caledonian Sleeper terminates.

Mallaig, because it is the terminus of all services and is around 39 miles from Fort William.

Oban because it is the terminus of all services and is around 42 miles from Crianlarich.

One concern I have with suggesting fast charging, yes, when things are going according to plan it'll all be fine, but as soon as delays start to occour you loose any flexibility of reducing turn around times and dwell times to claw back time... unless I'm missing something?

 

[Falcon1200]

Crianlarich because of the long wait times due to the splitting and joining of the Oban and Mallaig portions of the train.

Trains which join or divide at Crianlarich have a 'long wait' of at most around 15 minutes - Is that enough for a charge? And many services do not join or divide there anyway.

 

[Nottingham59]

Trains which join or divide at Crianlarich have a 'long wait' of at most around 15 minutes - Is that enough for a charge?

Stadler say their Flirt Akku recharges from the OHLE in 15 minutes. That supposedly gives an operating range of "up to 150km". See:

FLIRT Akku battery electric multiple unit | Stadler

Stadler's battery electric multiple units (BEMUs) are designed for non or partially electrified routes.

www.stadlerrail.com

 

[AlastairFraser]

I would imagine the 153s will stay and will be paired with the 158s instead of the 156s on the West Highland Line, as the 158s will be freed up from the Fife Circle and Borders line. Electric borders frees up six sets (2tph with 3-hour round trip), probably another five on Leven (1tph with 5-hour round trip), and another three to four sets on Cowdenbeath (1tph with 3-4-hour round trip). The freed-up sets will be a mixture of 158s and 170s, with the 170s taking over existing 158s services to enable 158s to work the West Highland Line. Based on a quick look at Real Time Trains.

If the West Highland Line goes to Battery units, then I would recommend fast chargers roughly every 30-40 miles at Crianlarich, Rannoch, Fort William, Mallaig and Oban.

Crianlarich because of the long wait times due to the splitting and joining of the Oban and Mallaig portions of the train.

Rannoch, because it is around 30 miles from Crianlarich, with a waiting time due to passing trains.

Fort William is around 35 miles from Rannoch, and it is where the units sit for 5 minutes to allow the driver to change ends to continue the trip on Scotrail services, and where the Caledonian Sleeper terminates.

Mallaig, because it is the terminus of all services and is around 39 miles from Fort William.

Oban because it is the terminus of all services and is around 42 miles from Crianlarich.

How are you going to get fast chargers installed at some of these stations? Rannoch and Crianlarich are very remote.

 

[BlueLeanie]

If the West Highland Line goes to Battery units, then I would recommend fast chargers roughly every 30-40 miles at Crianlarich, Rannoch, Fort William, Mallaig and Oban.

Why?

Ember coaches have already travelled 140km to get to Crianlarich before they continue the next 80km to Fort Bill. They can go over 300 miles on a single charge.

If a luxury Chinese built electric coach can go over 300 miles on a charge, surely a train can manage more than 30 miles?

Time to get Yutong on the case and build some bespoke units for Scotrail. Maybe a stretch of knitting up at Oban and Fort Bill to recharge?

Just imagine, the Chinese engineers probably have a method to have a unit cozy at Oban on a chilly morning - something that has evaded British engineers.

 

[Trainbike46]

For the West Highland line, and the Far North and Kyle of Lochalsh lines, the short term solution is to use existing DMUs (156s/158s/170s, depending on suitability).

The long term solution is, in my view, a BEMU with extra large/more batteries for the long runs, paired with some strategically located charging solutions. That might end up being a separate procurement though!

One way in which charging facilities could be installed is similar to the DART+ facilities at Drogheda (link to images of construction here).

When the BEMUs being come into service, they will likely cascade most (possibly even all) 156s/158s to metal recycling, with the remaining diesel services run by 170s (and 222s until the IC units get replaced as well).

Trains which join or divide at Crianlarich have a 'long wait' of at most around 15 minutes - Is that enough for a charge? And many services do not join or divide there anyway.

You can get a lot of energy in a battery in that time.

 

[GusB]

Not being familiar with the whole West Highland line, how much wiring is there between Queen Street high level and Helensburgh (which I believe is where wiring ends - please correct me if I'm wrong)?

Using the above-mentioned Stadler Akku as an example, with a range of up to 150km (approx 94mi), it's not quite enough to get all the way from Queen St to Oban (101.15mi*) on a single charge. From Queen Street to Fort William (122.36mi), a unit would definitely need a top-up charge along the way and it would probably make sense to have charging facilities at Crianlarich where dwell times are longer. If there's enough of an opportunity to charge before Helensburgh it may not even be necessary for the Oban-bound unit to top-up there.

The Fort William/Mallaig-bound unit should be able to take on enough charge to get it to Fort William where it would be able to top-up again before departing for Mallaig. Charging facilities at Rannoch would probably be unnecessary, although may be useful and easier to get a connection. There's lots of electricity infrastructure in the vicinity. I'm probably being over-simplistic here, though!

Of course, battery technology is rapidly improving and when (if) any of this comes to fruition it may well be possible for a unit to do Glasgow to Fort William on a single charge.

* Distances taken from Realtime Trains.

 

[Richard123]

One concern I have with suggesting fast charging, yes, when things are going according to plan it'll all be fine, but as soon as delays start to occour you loose any flexibility of reducing turn around times and dwell times to claw back time... unless I'm missing something?

A BEMU would slash journey time compared to diesel on these routes. More than compensating charging dwell time.

140 miles isn’t that far beyond current tech. A single high powered charger may well be comfortable for a boost each way.

 

[BerkshireRails]

Trains which join or divide at Crianlarich have a 'long wait' of at most around 15 minutes - Is that enough for a charge? And many services do not join or divide there anyway.

The GWR fast charger can recharge the class 230 unit with up to 2 megawatts at a time. Fifteen minutes is a long time when you consider that most station stops on the network are only for a few minutes.

How are you going to get fast chargers installed at some of these stations? Rannoch and Crianlarich are very remote.

Maybe renewable power and/or a grid supply would be a good idea.

Rannoch and Crianlarich have TPWS Grids, which require electricity; where does the power come from to supply the uninterruptible power supply?

Provision of TPWS​

The most significant development on RETB lines since commissioning has been the fitment of the Train Protection & Warning System (TPWS) in 2003. This has greatly increased the amount of external infrastructure. Each TEP where TPWS is fitted requires an uninterruptible power supply, a 'Trackside Radio Control Unit' (TRCU) and a mast supporting two RETB radio antennae. The equipment will 'listen in' to the exchange of tokens between the control centre and trains over the radio and determine which TPWS loops at that TEP should be energised and which can be de-energised for an authorised movement. A 'Lineside Status Indicator' (LSI) is mounted on each TPWS-fitted stop board. This comprises a blue light which is normally steady but which flashes when the associated TPWS is disarmed. A repeater LSI may be fitted to the corresponding distant board if the stop board can be approached at speed, e.g. at an intermediate TEP without a crossing loop.

At a crossing loop TEP, TPWS loops are installed at both ends of each loop line. Most RETB crossing loops in Scotland were originally only provided with stop boards for trains departing from the loops in the usual direction. Concurrent with the installation of TPWS, new stop boards for opposite departure direction were installed as necessary so that every TPWS fitment has an associated stop board on which to mount an LSI.

If a luxury Chinese built electric coach can go over 300 miles on a charge, surely a train can manage more than 30 miles?

Although battery units can do 80-100 miles between charges in regular service, I think it is better to have a few charging stations within the maximum range, so in case one charging station fails, you can still get to the next charging station without load shedding. It also allows the battery to be topped up in a shorter time, as less power has been used in transit between the stations.

I have noticed that the West Highland Line has a 15X differential speed rather than MU (Multiple Unit) or SP (Sprinter, which includes the Networkers and Turbostars). Does anyone know why?

 

[BlueLeanie]

A BEMU would slash journey time compared to diesel on these routes. More than compensating charging dwell time.

140 miles isn’t that far beyond current tech. A single high powered charger may well be comfortable for a boost each way.

I'm still confused why Rail batteries are so poor compared to Coach batteries.

The Yutong GTe14 that cruises between Edinburgh and Fort William has a 560kWh battery (630kWh option) and weighs in at 24 tonnes at just under 14 metres long.

So if two of these batteries were slung under a 23 metre unit, it would give between 1120kWh and 1260kWh of energy available.

A 170 has a 315kW engine, so a similar powered electric motor could run continuously for 4 hours at maximum power on a 1260 kWh battery.

Is it the case that in order to travel from Glasgow to Fort Bill a current 170 would have its diesel engines running at maximum power continuously for 4 hours?

 

[TheWierdOne]

With the prospect of floating wind turbines with directly connected electrolysis pods coming to market, Scotland may have a reliable supply of cheap renewable hydrogen that will be viable for lines like the Far North and West Highland that have no realistic prospect of electrification.

The problem with hydrogen is that it is very difficult to match the energy density of diesel. Hydrogen is much trickier to store in sufficient quantities to get the range of a DMU, whereas battery technology has come on in leaps and bounds in terms of the amount of energy you can squish into a box.

 

[AlastairFraser]

The problem with hydrogen is that it is very difficult to match the energy density of diesel. Hydrogen is much trickier to store in sufficient quantities to get the range of a DMU, whereas battery technology has come on in leaps and bounds in terms of the amount of energy you can squish into a box.

That's true, but a Coradia iLint hydrogen MU currently in operation in Germany has a range of 370 miles minimum, and a top speed of 87mph (more that sufficient for a line with a 70mph line speed limit).

In addition, you've highlighted that the technology is only going to improve over time - perhaps energy density won't, but fuel cell efficiency is very likely to improve and adding OHLE capabilities will extend capabilities (it's around 23 miles from Glasgow Queen St to Craigendoran junction - assuming the Maryhill line will be electrified as infill at some point, that gets the mileage on hydrogen down to 78.17 miles from Oban and 140.66 miles from Mallaig).

With a hydrogen refill station at Oban/Mallaig/Glasgow Queen St, range should never be an issue.
You also have the additional advantage that wiring the approximately 4 miles unelectrified section on the Maryhill Line allows you to banish DMUs from the Glasgow suburban network and standardise on OHLE units.

I do think batteries are suitable for the vast majority of the future rural unelectrified network, but the Far North/West Highland/Kyle of Lochalsh lines being very isolated and lengthly routes through some very remote areas helps the case for 10-20 units of hydrogen bimode MUs to solve the decarbonisation challenge on those routes, while taking advantage of the development of the local Scottish green hydrogen industry that is rapidly advancing.

Edit: I thought I'd add some links about green hydrogen projects close to the routes I think are suitable for hydrogen bimode units.
1.) https://storegga.earth/en-gb/speyside-hydrogen (Ballindalloch, about 50 miles off Inverness, so potentially useful for the Far North/Kyle of Lochalsh lines).
2.) https://www.cromartyhydrogenproject.co.uk/ (Cromarty, just 25 miles away from Inverness - useful for the Far North/Kyle of Lochalsh line).
3.)https://www.gov.uk/government/news/...oject will be,of water, using renewable power. (Whitelee windfarm hydrogen project, about 12-15 miles outside of Glasgow).

The Far North line also would have reasonably close access to the existing green hydrogen production project on Orkney.

 

[stevieinselby]

I'm still confused why Rail batteries are so poor compared to Coach batteries.

A class 156 has about 2–3 times the fuel consumption of a typical 50 seater coach. Yes, steel wheels on steel rails is more efficient than rubber tyres on tarmac, but you're moving 78t of train plus up to 150 passengers and luggage, compared with a diesel coach that only has to move maybe 15t of coach plus 50 passengers and their stuff – that weight differential will be just as true when you're looking at a battery-electric train against a battery-electric coach, you'll need 2–3 times the battery capacity to give the same range, but that might not be so easy to fit, as trains have to fit within the loading gauge so you can't just enlarge the physical envelope of the vehicle to create more space for batteries.

 

[BlueLeanie]

A class 156 has about 2–3 times the fuel consumption of a typical 50 seater coach. Yes, steel wheels on steel rails is more efficient than rubber tyres on tarmac, but you're moving 78t of train plus up to 150 passengers and luggage, compared with a diesel coach that only has to move maybe 15t of coach plus 50 passengers and their stuff – that weight differential will be just as true when you're looking at a battery-electric train against a battery-electric coach, you'll need 2–3 times the battery capacity to give the same range, but that might not be so easy to fit, as trains have to fit within the loading gauge so you can't just enlarge the physical envelope of the vehicle to create more space for batteries.

An Ember Coach is an electric coach, they too are gauge limited in size length, width and height to fit on UK roads.

24 tonnes of coach including 300+ mile battery plus 50 passengers.

A class 156 has a 215kW engine, so that's powerful enough to move a 38 tonne coach on the WHL. So one Embar coach battery would be enough to run a single 215kW motor, for 2.5 hours, and two Embar Coach batteries would be enough to run a 215kW at electric motor at maximum power continuously for 5 hours.

I'm not even sure if the 215kW on the plate of a diesel engine in a train is the output power.

 

[Falcon1200]

A BEMU would slash journey time compared to diesel on these routes.

How? The constraints on West Highland Line journey times are the geography of the route and the single line, not the type of train in use.

 

[BlueLeanie]

How? The constraints on West Highland Line journey times are the geography of the route and the single line, not the type of train in use.

Isn't geography the exact reason why a BEMU would help? Lots of lovely immediate and continuous torque from an electric motor.

Not sure if your area has switched to any electric buses, but goodness they move compared to the heritage kit.

 

[MadMac]

Not being familiar with the whole West Highland line, how much wiring is there between Queen Street high level and Helensburgh (which I believe is where wiring ends - please correct me if I'm wrong)?

Wiring runs from Queen Street-Cowlairs then Westerton-Craigendoran.

== Doublepost prevention - post automatically merged: 11 Sep 2025 ==

Rannoch and Crianlarich have TPWS Grids, which require electricity; where does the power come from to supply the uninterruptible power supply?

Those use minimal power. Crianlarich has an existing signal power supply for the junction - Rannoch probably has similar.