Amongst other factors that led to Detroit's economic demise,, the railroad that I worked for (Penn-Central) became a government supported entity that in order to receive funding, was forced to absorb several other failing but smaller railway companies, such as the Detroit Terminal, and others whom I can't recall from my faded memory of the late 70s. The new railroad was named Conrail, with its HQ in Philadelphia.
After Conrail finally made a profit for the first time in '80, it like Chrysler and much later GM was eventually taken off federal "life support". Conrail began to cut its workforce moving most jobs that were not physically necessary to be located @ local and longer haul freight operations to its HQ. This eventually resulted in the abandonment of the MCS except for Amtrak-related operations,
Eventually in the late 80s, Conrail was broken up and most of its equipment was sold to Canadian National and CSX. CSX then built sidetracks to newly/recently built foreign automakers' plants and factories in the South, which saved them millions if not billions in shipping costs, since it was MUCH cheaper to ship to the NE, Midwest, and NW/SW via rail than by using individual semi-trailer trucks.
This of course permitted the foreign automakers to grab an ever-increasing share of the automotive market in the US, while accelerating the decline of the domestics, with the most notable being AMC who soon went belly up. Another well-know railroad based in MI went out of business named Grand Trunk (whose name was "borrowed" by the popular MI rock band un the early 70s, being Grand Funk RR).
Automotive and related jobs in the Detroit metro area and outstate (Flint) began to disappear, creating a domino effect upon other businesses indirectly dependent upon the automotive industy By the mid-80s there were hundreds of thousands of native Michiganders soon being forced to move out of state to find employment. In TX, where many Michigan residents had traveled to to seek jobs, they were (often derisively) called "black-taggers" by native Texans.