Mount it to street light poles, or the side of an elevated subway line.
Rail at about 25 ft high so the bottom is about 20 ft above extra tall semis.
A steering lever so you can go right or left at an intersection or right into a station in midblock.
A mechanism to redistribute empty cars (electric battery & automated steering).
Automated merge control and braking to limit contact speeds to 5mph.
Basically an elevated Divvy system.
Wait, a no oil powered mass transit?
The big oil companies are burning Styrofoam as they see this.