A diverging diamond interchange (DDI), also called a double crossover diamond interchange (DCD), is a subset of diamond interchange in which the opposing directions of travel on the non-freeway road cross each other on either side of the interchange so that traffic crossing the freeway on the overpass or underpass is operating on the opposite driving side from that which is customary for the jurisdiction. The crossovers may employ one-side overpasses or be at-grade and controlled by traffic light. The diverging diamond interchange has advantages in both efficiency and safety, and—despite having been in use in France since the 1970s—was cited by Popular Science as one of the best engineering innovations of 2009 and in the U.S. has been promoted as part of the Federal Highway Administration's Every Day Counts initiative. The flow through a diverging diamond interchange using overpasses at the crossovers is limited only by weaving, and the flow through an implementation using traffic lights is subject to only two clearance intervals (the time during which all lights are red so that the intersection may fully clear) per cycle. The greatest safety concern of the interchange stems from its relative rarity, as drivers instinctively trying to stay on the customary side of the road could use the crossover intersections to turn against the posted direction of travel. This is a rare occurrence; it is possible only when traffic is so sparse that no cars from the oncoming direction are stopped at the light, and clear signage further reduces the likelihood of such errors. History The first known diverging diamond interchanges were in France in the communities of Versailles (A13 at D182), Le Perreux-sur-Marne (A4 at N486) and Seclin (A1 at D549), all built in the 1970s. The ramps of the first two have since been reconfigured to accommodate ramps of other interchanges, but they continue to function as diverging diamond interchanges. The interchange in Seclin (at ) between the A1 and Route d'Avelin was somewhat more specialized than in the diagram at right: eastbound traffic on Route d'Avelin intending to enter the A1 northbound must keep left and cross the northernmost bridge before turning left to proceed north onto A1; eastbound traffic continuing east on Route d'Avelin must select a single center lane, merge with A1 traffic that is exiting to proceed east, and cross a center bridge. All westbound traffic that is continuing west or turning south