Cross-border review of rail network officially launched

Please keep sectarian politics out of this discussion. If the “cross border rail” you’re referring to is the suggested Mullingar-Portadown link, then it’s actually the NI section that is more likely to go ahead without the “south” rather than the other way around. Portadown-Armagh is a much more viable proposition than Mullingar-Cavan, let alone Mullingar-Clones.

Hmmm, yes, that's exactly what the Irish tender says. I was wondering where I got the idea that was more than “nice to have”, then I see that on the UK side, the tender notice ( Enterprise Fleet Replacement Project [Notice] ) it says something slightly different:

Initial traction power will be Internal Combustion Engine (ICE) Battery Electric (using the existing 1.5 kV DC OHLE) with the train designed to transition to a net zero carbon operation during its life by the removal of the diesel power generation for replacement with dual OHLE power supply equipment.

Note the additional word “Battery”, and that 1500 V operation was considered a baseline requirement. That said, I believe the Irish notice on etenders is the definitive one, as IÉ seem to be running the tendering.

I agree that future mainline electrification will be 25 kV AC, but in order to run on OHLE into Dublin on the Northern Line, the Enterprise trains will have to be capable of 1500 V DC operation too.

I expect that all other inter-city electric stock in the Republic will be dual OHLE because otherwise the fleet will be split between “into Connolly” (AC and DC) and “into Heuston” (AC only) sets, as only Heuston will have a dedicated inter-city tracks that could be electrified at 25 kV AC; all approaches to Connolly are going to be 1500 V DC after DART+. That kind of split creates operational problems where none should really exist, so my own thoughts are that in addition to all stock being dual OHLE, the Greater Dublin Area will also be exclusively 1500 V on all tracks so that any OHLE train can be routed anywhere around Dublin under its own power.

One quirk about the Enterprise call for tenders is that the top speed is requested as “minimum 180 km/h”, while the long-term plan for this line is 200 km/h within the lifetime of these trains. Fortunately, most manufacturers’ products fall into categories with maximum speeds of 160, 200 or 250 km/h, so we’ll probably end up with a 200 km/h trainset anyway.

Pretty much that.

Theoretically, the 1500 V DC DART trains could be adapted to be dual voltage too, but this makes each one more expensive and also a little less efficient. Those differences add up when you’ve got so many DART trains, running so many journeys every day, so in practice I’d expect that they won’t do this, and instead any “far commuter” services to be run using dual-voltage EMUs that work at 25 kV outside the “DART area” and 1500 V inside.

Making longer-distance trains dual-voltage has the same penalty as making DARTs dual voltage, but those trains make fewer journeys, don’t stop and start as often and are generally heavier anyway, so the additional “cost” is outweighed by the benefit of being able to run on both OHLE systems.

Having to deal with two electrification systems is down to history: back in the late 1970s, DART was specified as 1500 V DC, not 25 kV AC - both were an option at the time, but 1500 V had some very clear cost advantages for an urban railway with the technology of the time. As there’s so little electrified rail in Ireland, the possibility of replacing the existing DART 1500 V system with 25 kV AC was considered during the early stages of DART+, but it was ruled out because it would have nearly doubled the cost of the electrification project, and worse, it would have needed the current DART service to shut down entirely for months while the existing line was swapped over.

Basically, adding extra a small extra cost to every long-distance train for the next century or so was cheaper than the enormous cost and disruption of ripping out the current DART and re-electrifying it as 25 kV.

Ireland will not be unique in having to use dual mode trains, as there’s several countries in Europe that have two electrification systems within their borders, and of course, rail travel between countries with different systems is commonplace:

The reason supporting two voltage standards isn’t such a big deal is because modern trains use AC induction motors, where the speed of the motor is determined by the frequency of the voltage applied to it. That means that no matter what’s on the overhead line, you’ll need electronics in the train to convert it into something useful: whether you provide two converters or one doesn’t change things hugely. Modern signalling systems have protocols for handling OHLE voltage changes safely.

25 kV at 50 Hz is the preferred system for new rail electrification across the EU, which is why it’s the most likely for us to adopt for mainline use.

North of Drogheda will be 25kV as is the plan with west of Hazelhatch so a dual powered fleet is needed.

The internal DC bus on most modern trains is around 1500v so dual voltage is fairly straightforward

The Drogheda to border section is a great candidate for the first rollout of 25kv AC with enterprise planned to be multi-modal. Means the service isn't dependent on the electrification being in place which mitigates against risk. They should start asap.

Translink already has their feasibility study and outline business case for Belfast to the Border.

In addition to this, would 1.5kV DC also struggle with the power needed for higher speeds? It is a limitation AISRR mentions, although I am not sure to what extend 1.5kV DC would actually affect top speeds.

There’s a recently-opened 1500V DC line in the Netherlands that is cleared for 200km/h running (Lelystad–Zwolle railway - Wikipedia); it appears the general service speed limit of 160 km/h on Dutch railways is due to signalling, not voltage: only trains fitted with ETCS are permitted to travel at 200 km/h on that new line. (DART+ stock and all future Irish trains will be fitted with ETCS)

1500 V DC is not the most cost-efficient way to electrify a new 200 km/h railway, but on the Northern line, they’re balancing the cost of electrification with the benefits of being able to run DARTs to Drogheda too.

It would make sense to finish 1500 kV to Drogheda now because it'll accommodate frequent darts. The proposed new Drogheda to Clongriffin line could be 25kV with only 1 stop at the Airport and less frequent service.

I don't think there is any situation where BEMUs would be operating to Drogheda beyond the lifespan of the batteries and I certainly didn't assume that. When the batteries are taken out, they could potentially be replaced by transformers etc. to allow the train to operate under both voltages (I don't know the technical implications of this). Advances in battery technology could even make replacing the batteries with the next generation a more attractive option when that time comes.

I'd assume there would be a significant cost saving in going 25kV AC from Malahide to Drogheda rather than 1.5kV DC. North of Drogheda will be 25kV anyway. With AC, it could be done as a single project all the way to the border which should also be better value than two smaller projects for different voltages. There should be significant cost savings with AC.

My point is that the BEMUs buy time and that we should be looking for the best solution for the line as a whole rather than just for getting electric trains as far as Drogheda (which is what D+ N is about). BEMUs have done away with the need for 1.5kV DC to Drogheda in the short/medium term at least, longer term I don't see any advantage in going with it either.

Another option could be to order more new Enterprise trains (which will have to be dual voltage) and use them for all services north of Malahide (assuming that will be AC).

Any cost savings or simplifcation in planning that could be made from using 25kV on the line would be lost from dual-voltage EMUs, especially if you are trying to convert existing units. AC+DC dual-voltage is quite a bit more complicated than just having a transformer, and typically needs a second pantograph. If for the IC network IE was advancing with MVDC such as 9kV DC, you might have more a point as they could use the same pantograph and could maybe be an easier modification, however that isn't the direction we are going with. Even then as much as I like MVDC tech for IC networks, I still believe 25kV AC is the best option for our IC network for a number of reason, the most important of which are that 25kV AC is the most common voltage for IC, and is what NIR is likely to use.

In addition to that, while there is an argument to be made about whether another voltage may be better for Drogheda-Malahide in an isolated bubble, the fact that Drogheda is supposed to join the DART network means that, long-term, no matter if 1.5kV is inferior, the best solution for Drogheda-Malahide is what the rest of the DART network is using. Avoiding AC+DC dual voltage makes the fleets cheaper, easier to maintain, and lighter, all of which are very important for a commuter fleet, though is not as much of an issue for IC fleets.

Another option could be to order more new Enterprise trains (which will have to be dual voltage) and use them for all services north of Malahide (assuming that will be AC).

This is very likely what they will do for the outer commuters (Dundalk, Longford, Portlaoise, etc), but not Drogheda. The requirements for an outer commuter fleet is much closer to the specs for an IC fleet(high speed, less stops, less frequent) hence why it isn't much of an issue. Especially here because the difference between an outer commuter and a regional/IC service can be very blurred.

But whatever unit they order, will almost guaranteed not be suited for a rapit-transit fleet. I know we are currently using 22Ks for short distance commuters on the Kildare line, but we really shouldn't be and it is done out of necessity. There is a very good reason why they are moving away from that as a part of D+SW. IC units are just not suited for RT services.

Well, the current plan and design is based on a desire to extend DART to Drogheda. Having DART trains running there made sense at the time due to being able to use new units procured for the expanded DART network, which meant extending the existing electrification. The ability for batteries to allow these new units run to Drogheda has removed the need to extend electrification until approx. 2040. Electrifying the line can be long-fingered for now.

In reality, Drogheda and several stops before it are too far out for high frequency urban city rail. In another country, they would be served by commuter trains serving much fewer stations (R&L station would be the limit for DART imo, it also has space for proper terminating platforms). As I mentioned in my post, and another poster too, we are likely to order new trains which will be suitable for this purpose and also be dual voltage. If we have such units operating on this line already, it would not be a huge cost to have more of them operating there and serving more stations. The units would probably be maintained in Drogheda anyway.

The other reason for simply extending DART to Drogheda was to do with capacity restrictions on the line. It was just easier to have one service operating through rather than multiple services with different stopping patterns. Options are being looked at to increase capacity and if that can be achieved, going back to separate DART and commuter services would make sense.

Btw, I am not saying that this is exactly what should happen. This is a discussion forum so I am discussing something. Things have already moved on from the original DART+ plan (i.e. BEMUs) and things will change further over the next decade. Assuming that by 2030 the bulk of DART+ has been delivered (D+ W & SW complete, N with the minimal changes at Malahide and BEMUs operating north from there, S still in planning but the arse cut out of it with the possibility of BEMUs operating to Wicklow), a new plan will need to be looked at from that standpoint anyway. There will still be scope for improvements from there which may be very different from what DART+ intended.

Yes, I see little point in discussing alternatives for electrifying Malahide to Drogheda. It's decided, it's happening as DC.

@PlatformNine regarding the proposed Crongriffin to Drogheda direct line, I agree that 1500 V is essential at the city end. The only question is at what point outside the Dublin area they would switch to 25 kV, if at all, on this line - like you, I suspect it would be DC all the way. I also see the Dublin area as being entirely electrified at 1500, regardless of what a given line is normally used for : the alternative would create a lot of needless headaches when moving DC trains around.