Dublin - Metrolink (Swords to Charlemont only)

Of course it’s required frequently. If you think of “the Metro” as a single object, it seems odd to suggest that it needs such frequent inspection and maintenance, but it is not a monolith: it’s a number of interdependent systems, each of which needs to be monitored and taken care of, and there’s only so much that can be done in parallel.

The track isn’t even one thing from a maintenance perspective: inspection and maintenance work on track is done in sections, so while any given run of track might only need to be inspected once every month, if the whole system is divided into thirty work areas (i.e., about 1km of track for each direction), then that means there’s a nightly inspection somewhere on the line. And it’s not just track: in between times, there’s electrical systems, signalling, train control, platform doors, ventilation, etc. etc.

This is a big system, there will always be something that needs looking at. Two hours a night, five nights a week won’t be wasted time, especially if it catches a serious problem early. If you sweat any machine and skip maintenance you risk complete failure and long downtimes. But doing this regular maintenance would allow the system to be confidently extended to all-day operation for those brief periods when this is actually needed.

New York is the only non-automated system that runs 24 hours, but it was built with long three- and four- track sections to facilitate this. NY was the world’s first underground railway, but no subsequent system followed its example - why? It wasn’t worth the extra cost.

Copenhagen is an outlier, and the 24-hour running is more of side-effect of the design allowing in-service daytime maintenance in the event of a failure than something that fulfilled an actual need. As with New York, it’s telling that no system built after Copenhagen adopted this design. Bigger cities than Copenhagen seem to get on fine with no need for 24-hour metros: Milan M5 is also a fully automated line, and it operates 18 and a half hours a day (0530-0000). Moving up to megacities, Paris is 05:30 to 01:40 on weekends, closing at 00:40 during the week, Tokyo runs night-buses rather than extending the operating hours of its metro lines, and Hong Kong MTR lines shut around 0100 and re-open at 0600.

If Tokyo cannot produce enough passengers in the middle of the night to make a metro line viable, then there’s no hope that Dublin can.

I think it’s a mixture of lack of demand and also cost. Tokyo’s urban rail has quite short opening hours: right now, Japan Rail urban services and Tokyo Metro open 20 hours a day from 05:00 to 01:00 (or 05:00 to 25:00, as the Japanese would say) while the Toei Subway runs 19 hours a day, from 05:00 to midnight. It would not be impossible for these lines to open for another hour or so per day, but neither operator does this outside of the New Year holiday period, when a sort-of 24 hour service is offered. I really don’t think this is entirely a technical limitation: there has been decades worth of continuous capacity improvement work across Tokyo, including new lines, but not once has there been anything proposed that would allow 24 hour operation. Even now, automation projects are concentrating on reducing headway during the morning and evening peaks, not extending the opening hours of the system.

My feeling is that 24 hour operation greatly increases the capital costs of the system, and the relatively small added ridership just doesn’t pay back those costs: when there’s very little traffic, as there is in the small hours of the night, road transport is more competitive than urban rail, simply because it can offer direct, door-to-door travel at very close to the same average speed; the cost-benefit analysis for overnight metro running can’t even count on savings from removal of road congestion, as no roads are operating anywhere close to capacity at these times.

It would be interesting to see the ridership figures for Copenhagen over the 0100 to 0400 period, and compare these to the number of people taking the city’s night bus network. My own feeling is that the design of Copenhagen’s metro was a decision to add resilience for daytime failures, and the ability to run 24/7 was just a side effect.