These are interstate highway numbers, and numbers connected with a line intersect. Some of the three-digit ones are ambiguous if taken alone, since they are used locally in multiple states, but when considered with all their intersections, each is unique. For instance, there are interstate 405's in California, Oregon, and Washington, and all of them meet interstate 5, but only the one in Washington also meets interstate 90.

Plot these on a map. The lines very roughly form the letters OCTET, which is the answer.