Arlington National Cemetery

Every day for five years, I drove through the most confusing spaghetti set of interchanges in the world, around Arlington National Cemetery and the Pentagon in northern Virginia. It is a bold claim, I know, but in an approximately four square mile area, there are: two interstates, four major divided/limited access highways, four bridges over the Potomac, and about two dozen interchanges. Of these, only one is normal, eight-way interchange. The other 20 interchanges all have some restriction: for example, there is an exit for northbound but not southbound traffic. Here, check out Google Maps for yourself:

Google Maps will navigate you through correctly (it has the correct information on the interchanges programmed in), but you can not tell anything about the interchanges from a static map. To help myself, I made an interchange (node) map:

Here is how to read it: If an interchange dot is colored black, both exiting and entering are possible. For example, in the lower right-hand corner of the map between G.W. Parkway northbound and I-395 northbound, you can see that a driver can exit from the Parkway to I-395 and enter the Parkway from I-395 because the lower right node of the interchange is black.

On the other hand, a colored dot indicates that it is only possible to enter the road of the dot's color. For example, at the top of the map, you can see that it is only possible to enter Spout Run from G.W. Parkway northbound and to enter G.W. Parkway southbound from Spout Run.

Please let me know if you find any errors! Check out this beautiful visualization.

Here is another post on network graphs and trail maps.