dedicated right of way for light rail, Bordeaux, France
One of the key ingredients for smooth traffic flow. Originally tram/streetcar tracks were laid along main city streets as there wasn't much competition from independently powered and steered vehicles. But as the latter increased in the 20th century the trams were in the way and they went. Modern thinking is that private cars should be kept out of city centres as much as possible.
See the earlier post on Bordeaux's modern light rail.