Strange as it sounds, self-drivable cars would eliminate most of the traffic jams. An interstate with no rubberneckers, accidents and slow drivers would be an efficient one. And we have the technology now.
That's one approach. Mine, is to eliminate the need for this many cars. But not in the same fashion that the control freaks in local government are forcing on us. Stricter licensing rules (no illegal alien drivers as a start, criminal drivers permanently banned). More buses, jitneys and taxis along with more lenient rules allowing more professional drivers. I mean, why can't you or I pick up carpoolers and earn extra money without requiring an expensive taxi license? A lot of stuff can be changed at the political level without the need for fancy expensive technology, like boondoggle high-speed trains to no where.