I'm not an expert. All I know about PRT is what is on the site I linked to and where the links there led. It just struck me as a good idea.
Even though a practical PRT system can only be car free, other forms of public transit, particularly trains, would still be needed to connect to the outside. Trains would still penetrate into a PRT area and can move a lot of people faster than a PRT system. Trains have always had a last mile problem and a PRT can go a long way to solving it. People using cars outside and PRT inside on a regular basis doesn't sound very practical. Maybe this could speed up the change. They say the popularity of the automobile peaked years ago. The century of the car has ended. They will still be around, like trains are still around, but they will not dominate our culture the way they do much longer.
Freight is another issue. Banning cars means banning trucks too. A lot of our freight now goes by truck. Trains could pick up some of the slack but they still have the last mile problem. A lot of factories and warehouses don't have a railroad siding. I suppose the PRT could be helpful there too. The site mentioned piggyback might be possible but I think rather than the whole PRT car, something like those storage pods you can get could be stacked on flatcars like containers on ships and offloaded onto some kind of flatbed PRT cars. That would use less cars and keep a better load density on the trains. Even so, we might need some highways to let trucks in to get to the industrial islands within the city. Once in the city, they could be separated from the PRT by grade (expensive) or time (inconvenient).
Most of this is my speculation, not theirs. How and where it could be done is beyond me but if it does happen in Detroit it will change the city in more ways than one. If it works very well the auto industry will take another big hit. I don't know whether a PRT industry could be enough to make up for it. Getting a jump on the rest of the country if the system is as beneficial as the designer claims just might be.