It is my belief that as originally planned I-75 was supposed to run closer to the river. This would be the reason that I-375 exists like it does and it was already built to Jefferson so they put it in use. I-75 curves three times in less than two miles, the interchange with I-375 and the Gratiot connector, the interchange with I-96 and another curve just after the I-96 interchange near the Ambassador Bridge. I think the route along the river was denied and what we have today is what we ended up with. It would make sense for I-75 to go all the way down to Jefferson, curving once instead of three times.
A long time ago i suggested that they remove all of I-375 and I-75 between I-94 and I-96 . This would remove all the freeways downtown except the Lodge. I never thought it was a good idea to do that but I was wishing downtown Detroit looked more like downtown Chicago. The problem today is that Detroit's freeway system was planned and built when the city had close to 2 million people so that is how the freeway system is built, it's overkill for today's population.
Let's not confuse a city's population loss with the traffic going through the city. As you well know, Flint and Saginaw have lost a massive % of their population the last several decades, but they sure get traffic through the area.
The cities lost population but the population just spread out pretty much. Like with Saginaw, the city had 98,000 in 1960 and Saginaw Township was a rural area, today Saginaw city has about 45,000 and Saginaw Township has about 40,000 everyone just moved further out but the population was still around. I noticed that Metro Detroit is more populated today than it was in 1950 when Detroit was at it's peak population. The inner cities should have done better at fixing the problems that the cities had, I'm not sure that Detroit has ever fully recovered from the 1967 riots I wish it would I'd love to see a city like Detroit booming again.
I've never been closer to Detroit than Ann Arbor. But I lived in St Louis for almost three decades. I think the problems of the two cities are similar but Detroit almost completely lost its white population (currently <10%) while St Louis is still fairly racially diverse (though still somewhat segregated with almost no white people living north of the
Delmar Divide). Most of the Central Corridor and the east part of the South Side are fairly integrated while the North Side remains primarily black and St Louis Hills in the SW corner of the city remains mostly white. While many of the poorer whites have moved to the suburbs/exurbs as have many poorer blacks (see
Ferguson), many city neighborhoods have undergone a rebirth and/or gentrified over the last forty years with people of all colors and backgrounds living along the Central Corridor and the near South Side. It was already happening in the 80's with the Central West End and Soulard, and now has spread to Lafayette Square, Midtown, DeBaliviere, Dogtown, and most recently Forest Park Southeast which has been rebranded as The Grove. In fact, the Central Corridor from Downtown to Forest Park along Highway 40 (I-64) is some of the most valuable property in the metro.
I don't know if this can happen in Detroit. I don't know if the economic base is still there. St Louis lost a lot of Fortune 500 over the years (General Dynamics and SW Bell moved, McDonnell-Douglas and Anheiser-Busch were bought out), newer businesses like Enterprise Rent-A-Car and Maritz have somewhat filled the gap and the old Anheiser-Busch Brewery is still going strong (in a continuing to gentrify neighborhood). Another comparison is Cleveland which also looked terminal but is also turning it around thanks to old anchors like the hospitals and museums around Case Western, new sports venues, the R&R Hall of Fame, and revitalized areas like The Flats. Cleveland also has several Fortune 500 companies and even pulled ADM out of Decatur, IL. The new sports venues and Corktown are good starts for Detroit but there's not much else going on.
To get back on topic, one good reason to remove I-375 is that it helps Downtown Detroit look more like Downtown Chicago. Of the current freeways only the old Congress, now the Eisenhower Expressway, was ever designed to enter the Downtown (through that iconic hole in the post office). The Kennedy/Dan Ryan is well west of Downtown and the Stephenson doesn't come close. One reason Downtown Chicago works so well is the El which radiates from downtown and moves a massive number of people; the Chicago Transit Authority moves 1.6 million people on an average weekday. Detroit only has that crap people-mover thing that never leaves downtown. Removing I-375 will also provide new housing stock. Some will bitch and moan that it'll become gentrified and drive out poorer residents. That happens but it's not like Detroit is lacking other inexpensive housing stock. The day Detroit starts worrying about too much gentrification is a sign that Detroit is coming back. That'll be a good thing.