In 2003, Ford Research proposed a dual-mode system called PRISM. It would use public guideways with privately-purchased but certified dual-mode vehicles. The vehicles would weigh less than 600 kg (1200 lb), allowing small elevated guideways that could use centralized computer controls and power.

(from Wikipedia PRT article)

Too bad noone has the vision to build something like this out.

PRISMGPCPaper.pdf (application/pdf Object)