Yeah I think it would be fine on commuter services, but there whould be too many complications on Intercity services, e.g. if you left Dundalk at 13:45 to arrive at Tralee at 21:00, how would the fare be charged? Peak, off-peak or part and part?
The trick with that type of ticket is to target the trips that people are likely to make quiet frequently, but not necessarily daily. That means trips of up to an hour within your own region. That means people are willing to spend something on it over the course of a year. It would suit a lot of leisure / social travellers.
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