Anthony Downs has written, extensively, about why not, and the people who build the roads may be catching on. For the visible evidence, check out this post from Travel and Trains.
That's the Katy Freeway in Houston, Texas, where there is no paralleling triple-track Katy Railroad commuter line to take the pressure off the expressway, the way the Wisconsin Division, which modern Chicago riders understand as the Union Pacific Northwest Line, relieves the Kennedy Expressway, and the Racetrack, relieving the Reagan Tollway and Eisenhower Expressway. (And even with the rail option, the Chicago expressways are often jammed both ways, even before the normal rush hour.) Although it appears that there is excess capacity in one direction, it's a good bet that all the cars waiting to go away from the camera will be waiting to approach the camera location either later in the day, or the next day.