The concept of road trains and super-smart-highways was presaged in John Varley's excellent 2004 novel Red Thunder. In the book, cars with higher optimal speeds (where aerodynamic drag and mileage gains of higher gear ratios cancel out) form faster trains, where inefficient vehicles are put in slower trains. The superhighways required cars to be equipped with the system to enter them, of course.
I concur with your projections, if only to add that social pressure not to waste fuel (by driving your SUV at 70mph rather than 50mph) will likely add the extra caveat of forcing one to drive at a reasonable speed.
And with all the automation of highways, we'll all get to our destinations faster, regardless.