An interchange is a gradeseparated intersection one road passes over another with ramps to connect them, as pictured. This is a Good Thing for busy roads; in the picture, thru traffic on the freeway red can pass through without stopping. Even if traffic signals are installed at the ends of the ramps, traffic on the surface street blue also flows smoother without interference from the freeway.

Website: http://www.kurumi.com/roads/interchanges/