Cross-border review of rail network officially launched

It's been explained several times now why this isn't going to happen. But to add another barrier : planning. The railway order for DART+ North includes substations for 1500 V DC power. If you wanted to change your mind and go for AC, the locations and type of those substations have to change, which means you need to go back to get new planning.. why would you do that?

In any case, there's no point in using 25 kV here as the long term future of the Dublin-Belfast inter city service isn't even on this corridor: the AIRR recommended a new, more direct, track routing from Clongriffin to Drogheda, which would make Malahide-Drogheda a DART-only line. If you want your 25 kV line to Drogheda, then that future direct link north of Clongriffin is the only likely option…

Thanks for the very interesting links.

While the SNCF slides suggest the 9000 V DC system as being “suitable for use by nations not yet electrified”, in Europe, that description really just means us (2,200 km in the Republic + 500 km in NI) and Albania (450 km)… hardly a huge area of opportunity, and we’re not even planning to electrify all of our network.

9000 V is a great way to increase the capacity and performance of a widespread 1500 V network without disruption to existing services, but I don’t see why any operator would start with that system if they had a free choice, as we mostly do. All of the infrastructural advantages 9000 V has over 1500 V also apply even more to 25 kV, because they are functions of using a higher transmission voltage. AC versus DC makes things a little more complex, but that complexity falls more onto the trains than the OHLE system itself. In a system like ours, with less than 100 mainline trains on the island, a higher cost per train isn’t actually that much of an issue.

9000 V may be “just as good”, but 25 kV AC is standardised, widely used across the world and is compatible with a wider variety of rolling stock. A railway the size of France’s can afford to go it alone with a different standard (and for them 9000 V is the sensible choice), but in a small railway like ours, where we’re already “special” thanks to our track gauge, we need to use as much off-the-shelf systems as we can to save money.

The determination is because, whether you realise it or not, you’re fast approaching a pattern that I could call “Metro through Drumcondra Syndrome”. A plan has been made and finalised, you offered a “what if” which was an interesting thing to talk about. We talked about it, and decided overall that there are more downsides than upsides, and that the people who designed the system were right. (Not a surprise: They are, as ever, working with far more, and far better, information than a group of people posting on a forum)

There’s been a lot of interesting responses to your original post, and I think everyone has learned a bit about why things were done the way they were, but we’ve also come to the conclusion that the proposal you made is a non-runner for lots of reasons. Persisting with the alternative becomes a little annoying because this isn’t a hypothetical discussion, it’s something that has already been decided.

To address your most recent points:

1. Electrification north of Malahide is highly unlikely to be pushed out beyond the 2030s. Northern is the lowest risk of not being electrified. Unlike W and SW, Northern electrification can be broken into small phases, and implemented one or two stations at a time, gradually extending the reach of EMU services until you get to Drogheda. W and SW are all-or-nothing projects that are more susceptible to delay due to their size.
2. The BEMUs are a stopgap solution, and if they stay as BEMUs they will be better used for service extensions out to Kildare and Enfield on W and SW once those lines are done. BEMUs are more expensive to buy and run than EMUs, they need expensive mid-life maintenance and cannot achieve the turnaround frequencies of EMU stock. Don’t get me wrong: BEMUs are great, and they’re a lifesaver on this project, but you really only should use them in specific cases.
3. It’s extremely likely that every rail line in Dublin will be electrified only at 1500 V. So even if you four-track the approach, any Enterprise trainset will always need to run off 1500 V - otherwise it cannot get in to Connolly. Whatever you do north of Malahide, Enterprise needs a 1500 V capability regardless.

The cost premium for dual-voltage trains versus single is smaller than you seem to think - a large proportion of European inter city stock is dual voltage simply because it has to cross borders: this is a commodity technology and a standard option on rolling stock: every train we could buy has been designed in a way that makes AC+DC operation cheap to implement if needed.

However, because dual voltage stock is a little heavier, and a little more complex, there is also a small operating cost increase too per journey. You have to make a choice as to which services will incur that operating cost: 20 inter city trains a day, or 200 DART trains a day? Trains use the most energy when accelerating to running speed, so, services that start and stop frequently will use more energy as dual voltage than as single voltage (the weight penalty makes acceleration more expensive). Also, regenerative return (sending electricity generated from braking back into the power supply) is less efficient on AC versus DC - only a little, but when you multiply it by a thousand station arrivals a day, it adds up. And the acceleration inefficiency also applies when these dual-voltage DARTs traverse the rest of the line too.

Then we look at operational complexity. Having a 25 kV DART service in addition to 1500 V means you need two sub-fleets: one single-voltage, one dual, unless you want to incur the extra cost of 25 kV running on lines that are entirely 1500 V.

Follow this reasoning through and you get to the only operationally sensible outcome: convert DART to 25 kV. This is neat, and solves the problems straight away. But it doesn't solve the problem of leaving Dublin without a DART service for a year while the changeover is put in place - and it also means having to buy more trains just to maintain the existing service levels. Full conversion to 25 kV was examined and emphatically ruled out in 2019.

As I said before, the proposal is gives a small initial saving, funded by decades of higher operating costs and more complex logistics.

Again, as I have stated in all my posts on this subject, I was not making a "proposal" rather just speculating on what could happen in the future given a critical component of the current plan has changed (the need for 1.5kV OHLE to Drogheda rogheda in order to provide electric train services to/from there).

Maybe DART+ will eventually be delivered exactly as planned, I never once said that it won't or shouldn't. My point is that the BEMUs make electrifying the Northern Line not necessary to operate DARTs to Drogheda until the late 2030s. That itself is a change from what was envisaged at the introduction of the DART+ plan. A reassessment at any time in the next 10 years could come to different conclusions based on changes which happen in the intervening years. Look at how the PPT was unsuitable for passenger services for years, then they decided it could be used after some works. Things changed!

I'm honestly not sure you have even read my posts. How you come to converting DART to 25kV is a mystery to me.