After almost two years of single-handed research, design, checking and cross-checking, I’m incredibly proud and thrilled to present my latest map project. It shows every single current and signed Interstate Highway and U.S. Highway in the contiguous 48 states in a style very similar to my previous Interstates as Subway Map and U.S. Highways as a Subway Map projects. Having made two separate maps that showed each type of road, I really had to at least try to combine them both into one map, didn’t I?

View the map in the window below: zoom in and pan around to get a good look. You can go full-screen by clicking the icon, or by clicking here.

However, I’d stop short of calling this a “subway map”. While still taking many design cues from that genre, I’d rather call it a “simplified road map” instead. Because of the insane complexity of the two combined networks, there’s a lot more adherence to geography here than in those previous, more stylised diagrams. Yes, the roads have been straightened out a lot – especially the Interstates – but many cities fall pretty much exactly where they would be on a “real” map, and roads cross state borders at or very near the correct locations. The overall shapes of the states have also been preserved as much as possible: you’ll see why soon!

The map follows much the same design principles as the previous ones: white circles with black strokes denote named places (cities, towns, etc.) where two or more roads intersect. The more roads at that location, the larger the dot. Named places at intersections are always shown, even if they’re just a teeny-tiny little hamlet. Not all roads meet at named places, so there are intersections with no labels. Places that fall along a road between intersections are shown as a “tick”, and are included if they have a population of 1,000 or over (thanks, Wikipedia!). Obviously, some places are left off the map for clarity in very populous urban areas, especially if they are considered as part of a “greater” metropolis: I apologise in advance if your home town is missing. There’s still an incredible 4,385 named places on the map!

Having to show different types of roads on the same map meant that an additional level of complexity was introduced. I decided that stroke width was the best way to differentiate between two-digit Interstate Highways (the thickest stroke at 8 points wide in my working file), three-digit Interstates (6pt) and U.S. Highways (just 4pt wide). As before, bright colours were assigned to the “major” routes as defined by AASHTO: these are two-digit routes ending in “0” and “5”  for Interstates, and “0” and “1” for U.S. Highways. The U.S. Highways use a lighter tint of the corresponding Interstate colour to differentiate between them if they ever run in close proximity (this is rare, but it does happen: I-55 and U.S. 51 share the same roadway out of New Orleans, for example). Four different greys are then used for the “minor” routes, with cool greys being assigned to odd-numbered routes and warm greys used for even routes. Minor Interstates are represented in darker greys than the minor U.S. Highways to reinforce their higher position in the information hierarchy.

Roads that touch on the map while running parallel to each other are actually sharing the same physical roadway: in AASHTO-speak, they are “concurrent”. Because of the scale of the map, I can’t always show where a U.S. Route might leave a concurrent Interstate to serve a town and then rejoin again immediately afterwards.

Roads that run closely parallel without touching are not concurrent, but are sharing the same corridor. This often happens where an Interstate has supplanted a U.S. Route as the main highway through an area. While I’ve tried my best to show these corridors as accurately as possible, there are instances where the roads are on the “wrong” side of each other compared to the real world. This is especially true when a winding old U.S. Routes cross and recross a (much straighter) Interstate highway multiple times in a short distance.

Needless to say, this map is physically huge. My working Illustrator file was a massive 144 inches wide by 88 inches deep and posters are half that size – the smallest they can be and still retain good legibility. So why did I make the map so big and insanely detailed? Why was it important that the individual states retain their actual shape? Because I’m also making posters of individual states and regions.

And yes, there are posters for sale! Check out both the USA map and the individual state maps in the Transit Maps secure on-line store.