While the US has its share of vehicles that can operate on rails or roads for quite a while, they’re all pickups for railroad maintenance:
Via Engadget, the Japanese do us one better. With rural villages shrinking, a Japanese railroad has developed a railbus that has two sets of wheels: steel for rail lines, and rubber to serve remote villages that are no longer economical to maintain rails to. Undergoing testing now, the railcars will cost $170,000 each. Those fancy new hybid buses Metro is running? $645,000 each.
These would certainly be some of the “unique vehicles” Ron Sims’ RapidBus BRT plans call for.