This is my imaginary island country of Regalia.

What kind of transportation would be feasible on this island? I imagined the country as a British colony settled in the early 18th century and gaining its independence after WWII. The population is around 1.8 million, though the overwhelming majority live in the twin cities of Kingsport and Arkham. The interior of the main island is sparsely populated and mountainous, with a few dormant volcanoes.

I'm trying to imagine the rail lines connecting all the cities on the south coast, and the ferry system between Kingsport and Arkham.