Documentary filmmaker Alison Walker recently created this great little history of the Roosevelt Island Tramway. The tramway was one of the only ways to get out to the island for over a decade until the F-Train subway stop was finished.
In about 1972, they realized that there was not going to be a subway in time for the opening [of the island], so the tramway was built as a temporary means for people to commute and it opened in May of 1976. The subway did not open until 1989.
Despite being designed as a temporary transportation method, the tramway is still in operation today and follows the same fare rates as the rest of the subway system.