The Dwight D. Eisenhower National System of Interstate and Defense Highways (Eisenhower Interstate System for short) spans the entire USA, including Alaska and Hawaii. The EIS serves all major American cities and has a total length of 75.376 km (2004). And yet most of it is represented here in this diagram so simple that it looks rather more like a subway map than a road map.

Some interesting bits of info about the EIS:

  • The EIS was initiated by Eisenhower in 1956, partly because he was impressed with the German system of Autobahns., which provided easy transport also for military purposes.
  • The system was considered complete in as of September 15, 1991, when the last traffic signal was removed from I-90 in Wallace, Idaho.
  • The accumulated cost of the EIS was $114 billion (original estimate: $25 billion).
  • Interstates are funded and regulated federally, but owned by the states. The only exception is the Woodrow Wilson Bridge on the Capital Beltway (I-95/I-495), which is federally owned.
  • The name ‘Interstate’ does not refer to the fact that these Highways cross state lines, but to the fact that they were funded federally. In fact, many don’t cross state lines. Best example: the Interstates on the island state of Hawaii.
  • Most Interstates have two numbers (I-4, I-5 and I-8 are the only single-digit Interstates). Three-digit Interstates are auxiliary highways.
  • Highways running east-west are given even numbers, those running north-south are assigned odd uneven. As a general rule, odd-numbered highways increase from west to east, and even-numbered ones from south to north. And highways divisible by 5 generally are bigger and longer than others.
  • A widespread urban legend states that one out of every five miles of the Interstate Highway System must be built straight and flat so as to be usable by aircraft during times of war; this is not true.
  • The most heavily traveled area of the Interstate Highway system is the 405 Freeway in Seal Beach, California, with a 2002 estimate of 377.000 vehicles a day. The least traveled section is I-95 just north of Houlton, Maine, with 1,880 vehicles a day (2001 estimate).

For info on the provenance of this picture, see first comment on previous post.