The middle of what?
The middle of the highway of course.
Forget about the rail design and imagine the top plate of an I beam flush with the road surface.
The idea would be to have a solid wheel/s automaticly deploy from underneath the carriage center of a vehicle or a truck which would displace a high percentage of the load to the solid wheel and a solid track giving advantage of less friction while still maintaining complete control of the load with the regular wheel set.
Obviously this would best be done with current technology, lane tracking, automation, etc to deliver best results and highest efficiency.
Food for thought.