The short story, off the top of my head, is that the federal government offered us close to $1B in the 70’s to build a regional transit system. There would have been subways/els down the spoke roads to Royal Oak and Dearborn, bus express lanes on the freeways (with stations in the middle at overpasses, like Chicago), commuter rail to Ann Arbor/Pontiac/Mt Clemens, with it all converging downtown with our own monorail loop to disperse riders between lines. Only the monorail loop was built because tribalism/racism/regional bickering delayed a plan from being agreed upon. The Feds kept the offer on the table for 3 presidential administrations before saying enough was enough. I think Atlanta or San Francisco got the money instead.

Commuter rail operated to Pontiac and Ann Arbor for a while, and was briefly tested to Mt Clemens, but they all stopped service in the 80’s. None of the expressway BRTs or spoke road rapid lines were built, obviously.