In fairness, the IAD Approach road was designed and built with the concept in mind (ie huge central median between the 4 lanes of the airport road and the outboard 6-8 lanes of Rte267 (Dulles Toll Toad)). Compare and contrast with the magnificent M25, linking (if you're lucky) LHR and LGW, and the wonders of the M40, M4 and M3. Forward vision, helped by available real estate, is of course helpful for our American friends - even if the money isn't there yet.