I think that public transportation commuting in much of Munster can be significantly improved by means of railcars (sometimes called “railbuses”), without the need to create completely new railroads, purchase any land, and much can be achieved even without putting down tracks where they were previously lifted.
I would suggest developing a railcar network over the existing Limerick-Limerick Junction-Waterford line, the Limerick Junction-Cork part of the main Dublin-Cork line, and the closed but in-situ Limerick to Foynes line.
Limerick to Foynes: not just freight
I’ll start with Limerick-Foynes. As Foynes is an active port, reopening the line for freight gets on the radar frequently. I suggest that to maximize the value of the investment it should be reopened for both freight and railcar traffic.
The station buildings, which were sold off, are not needed, as the railcar should be operated as a diesel tram. It should have unattended platforms with automatic ticket machines, and also support the Leap card. Car parking should be provided at the platforms. Railcars should run a few times per day to support typical work commute times; there should also be a late railcar, starting from Limerick about 10.30-11pm, to support people going for a night out in town.
Apart from the traditional stops on this line, a new stop, if not two, should be added to serve Raheen Business Park and the leafy Raheen-Ballysimon housing estates.
As the line is single-track, the service can not really be frequent, but that’s fine. About 4 trains in each direction (early morning, late morning after school run, commute evening, and late night) would do a lot already. Freight can use the line the rest of the time.
An inexpensive restoration of the line is likely to result in a 40 mph (60 kph) speed limit, but even that is not a huge issue, as the railcar would still deliver good time in peak hours because it avoids traffic. Ideally, of course, the restoration should aim at a 60 mph (100 kph) speed limit on most of the line.
Limerick to Waterford: super low hanging fruit
There is already a railcar-type service from Limerick to Limerick Junction linking up with trains to Dublin and Cork and, twice a day, to another railcar service to Waterford.
It would take very small effort to add platforms at Dromkeen, Pallasgreen, and Oola. Again, these platforms should operate as unattended stops (I think the railway term is a “halt”) with automatic ticket sales machines; the Leap card should also be supported. This would increase travel times for linked services by a few minutes, but would create commuting opportunities for many people; with reasonable car parking this would cover a pretty vast area.
The Limerick Junction to Waterford service already has well-placed intermediate stops in major towns. However the service itself should be increased to 4 times a day to enable commutes to Waterford; right now it seems to be optimized solely for commutes to Limerick as the earliest service arrives to Waterford at midday.
Cork to Limerick Junction (on to Limerick): bringing towns onto the network
Between Limerick Junction and Cork, a few significant towns, such as Kilmallock, Buttevant, Blarney, are close to the track but not served by the railway.
This happens because the intercity service is time-critical. Adding stops to this service would mean slower travel between the first and second cities of the Republic of Ireland.
My suggestion would be learning from continental Europe: running an intercity service and a commuter service on the same line. Indeed something like that is already implemented on the very same line between Dublin Heuston and Portlaoise. But in the case of Munster, the commuter service is probably best off as a railcar, which, again, enables small unattended platforms.
My suggestion would be running a railcar between Cork and Limerick via Limerick Junction, stopping at every town, while the intercity service continues at its present schedule of stops. As the railcar is slower and schedules are not always perfect, facilities to put the railcar on a side track and let the intercity pass shuld be provided at Limerick Junction and Mallow. Ideally, this railcar would also take over the current arrangement of synchronized passenger transfer from Limerick to Dublin and Cork intercity trains and back. Railcars already run from Mallow to Cork; some (or all) of the runs could instead be all the way Limerick-Junction-Cork and back, and additional Mallow runs could be added if necessary,
This would enable both Cork and Limerick commutes for the towns brought into the service, while keeping or extending the coverage that Mallow now has.