I found an excellent diagram of the U.S. Interstate highway system on strangemaps’ blog. Although the post doesn’t say who originated the diagram, the discussion is excellent. [Update: strangemaps' previous post has a comment noting the map's source (http://www.chrisyates.net/store/fullinterstatemap-web.jpg), and indeed the image itself is signed Chris Yates 2007.]
However, there are numerous technical errors and omissions on the diagram. It appears the original artist intended to include all of the one- and two-digit interstate highways (as evidence, I see that he included the single-state I-4 and I-16 in Florida and Georgia, respectively), and that he intended to label cities at intersections of interstates. Along those lines, the deficiencies are listed below.
- Route errors:
- The intersections of I-90, I-94, and I-25 (originally labeled Butte, Billings, and Buffalo) are all scrambled.
- The intersections of I-8, I-10, I-17, and I-19 (originally labeled Phoenix) are all scrambled.
- I-20 intersects I-10 almost 200 miles east of El Paso.
- Columbia is indeed at the intersection of I-20 and I-77, but nowhere near I-95 as shown.
- I-93 does not intersect I-91 at White River Jct, but rather much farther north.
- I-87 and I-89 do not exit the country together.
- Erie is indeed at the northern end of I-79, but that is at the intersection with I-90, not I-80.
- Almost all the routes in Pennsylvania are messed up (currently labeled Pittsburgh and Harrisburg).
- All of Wisconsin is missing.
- Many interstates in Illinois are missing, as well as others scattered around the nation.
- I-65 does not continue north past Chicago/Gary to Grand Rapids, and in fact the west end of I-96 is Muskegon, not Grand Rapids.
- I-75 does not end at Ft. Myers, but rather extends to intersect with I-95 at Ft. Lauderdale.
- Other erroneous cities:
- Wilkes-Barre is not at the I-80/I-81 intersection.
- Raleigh is not at the I-95/I-40 intersection.
- Winston-Salem is not at the I-77/I-40 intersection.
- The intersection of I-20 and I-95 is at Florence.
- The intersection of I-70/I-15 is not at a city, town, or village named Monroe.
- Las Vegas isn’t at an intersection, so it shouldn’t be shown.
- Missing routes:
- Part of I-94 is missing. It continues east of Minneapolis/St. Paul, to join with I-90 for awhile, then splits again at Madison WI, where I-94 heads east to Milwaukee WI and then south to the Chicago IL metropolitan area.
- Part of I-84 from Newburgh NY to its terminus in Massachusetts at I-90 is missing.
- I-64 east of I-95 to the Norfolk area is missing.
- I-40 east of I-95 to Wilmington is missing.
- I-76 from Pittsburgh to Cleveland is missing.
- Entirely missing are everything in Wisconsin, much of Illinois, and various regional and single-state highways: I-H1,H2,H3*, I-12*, I-24, I-26, I-27, I-37, I-39, I-43, I-49, I-59, I-72*, I-74, I-82, I-97, and I-99.
So I have modified the map greatly, as shown below. I have extended each highway to its actual end, or where it extends into Mexico or Canada, including the last major city, if any. Still missing are I-12 (a bypass around Lake Pontchartrain, north of New Orleans — in fact this was the original route of I-10, and the piece connecting down to N.O. was called 55 and 59), and I-72 in Illinois, for which there just isn’t room, and the Hawaiian highways I-H1,H2,H3.
[updated 19 March 2007] Moved I-64 south, between Staunton and Charleston; replaced El Paso with Las Cruces; replaced Portland (ME) with Houlton; labeled the blank dots at Green Bay and Blacktown (PA); merged Ft. Lauderdale into Miami; extended I-69 and I-94 to Port Huron; added more intersection names along I-10, I-39, I-57, I-69, I-70, I-77, I-80, I-81, I-82, I-90, I-93, I-95, I-99; completely revamped the WI-IL-IN-MI area to separate Chicago and Gary and clean up (slightly) the IL bramblebush, and adding I-72 and I-88; added I-12.
