This is something I'd like to see more thought on in the United States. The
Tram Train:
Netherlands has been building a intercity light rail network for the past years, reusing previous sections of tram lines, metros and heavy rail and extending them with new sections of elevated rail and tunnels. The RandstadRail currently operates on the southern region of the “round city”, namely connecting the Hague to its suburbs and Rotterdam.
Check out the photos at the link. I think it's a great idea to have regional railways that turn more into light rail in city centers. This is what Austin would have had to a certain degree with the first light rail proposal in 2000. A light rail line with limited stops in the burbs with greater connectivity in the center city.