I grew up with the sound barrier for 66 in my back yard and lived in the area for 30 years. It was absolutely completely open and then a single lane HOV and then HOV at certain hours in certain directions and now the express lane toll.
Not just more occupants per vehicle but more efficient use of road space. You can fit 4 motorcycles in the space it takes for 1 car. Look at the biggest metropolises in the world and motorcycle use is significantly higher than in the U.S.