The purpose of this map is to demonstrate the unseen logic of the numbering system that underlies the United States' legacy network of numbered highways.
This map uses publicly available data from OpenStreetMap displayed using Mapbox GL JS.
Original Interstate map created by Curt Arledge and modified by Jonathan Bittner.
Additional sources: Wikipedia.com, highways.dot.gov, Interstate-Guide.com
The US Highway System, is a network of highways in the United States of America. The system was first authorized by the Federal-Aid Highway Act of 1956 and supported by President Eisenhower, for whom it is named. The Interstate route marker is a blue, red, and white shield with the word “Interstate” at the top.
Interstate highways are owned, built, and operated by the US states, with funding aid from the federal government. State highway departments work through the American Association of State Highway and Transportation Officials (AASHTO) to assign numbers to new US highways.
Primary US Highway routes are designated by one- or two-digit numbers. Routes with numbers ending in 0 or 1 are intended to be major arteries, extending from coast to coast or border to border (though many do not).
Geographically, US highway route numbers increase from northeast to southwest, with the lowest numbers in the north and east of the country and the highest numbers in the south and west
Odd route numbers are used for primary routes running generally north-south, while even route numbers are used for primary routes running generally east-west.
Auxiliary Interstate routes are designated by three-digit numbers, each comprising a parent primary route plus a prefix.
Lowest numbered primary US Highway: US 1
Highest numbered primary US Highway: I 101
Lowest numbered auxiliary Interstates: I 105 (CA) and I 105 (OR)
Highest numbered auxiliary Interstate: I 990 (NY)
Longest Interstates: 1. I 90 (3,020.5 miles), 2. I 80 (2,899.5 miles), 3. I 40 (2,555.4 miles), 4. I 10 (2,460.3 miles), 5. I 70 (2,153.1 miles)
Shortest primary Interstates without planned extensions: 1. I 97 (17.6 miles), 2. I 2 (46.8 miles), 3. I 86 (Western) (62.9 miles), 4. I 19 (63.6 miles), 5. I 66 (76.28 miles)
Primary Interstates that serve only one state: I 2, I 4, I 11, I 12, I 14, I 16, I 17, I 19, I 27, I 37, I 43, I 45, I 73, I 86 (Western), I 87 (Northern), I 87 (Southern), I 88 (Western), I 88 (Eastern), I 96, I 97
Unsigned Interstates: I 305 (CA), I 910 (LA), I 315 (MT), I 124 (TN), I 444 (OK), I 345 (TX), I 478 (NY), I 878 (NY), I 194 (ND), I 495 (ME), I 595 (MD), I 296 (MI)
Interstate numbers shared by two distinct routes, with no plans to connect: I 76 (Western) & I 76 (Eastern), I 84 (Western) & I 84 (Eastern), I 86 (Western) & I 86 (Eastern), I 87 (Northern) & I 87 (Southern), I 88 (Western) & I 88 (Eastern)
States with the most Interstate mileage: 1. Texas (3,233.45 miles), 2. California (2,455.74 miles), 3. Illinois (2,169.53 miles), 4. Pennsylvania (1,759.34 miles), 5. New York (1674.73 miles)
States with the most Interstate highways: 1. New York (29 routes), 2. California (25 routes), 3. Illinois (23), 4. Pennsylvania (22), 5. Ohio (21)
Interstates that travel through the most states: 1. I 95 (16 states), 2. I 90 (13 states), 3. I 80 (11 states), 4. I 70 (10 states), 5. I 10 (8 states)
Only four state capitals are not served by an Interstate: Juneau, AK; Dover, DE; Jefferson City, MO; Pierre, SD
The only auxiliary Interstate without an existing parent Interstate: I 238 (CA)
The shortest auxiliary Interstates: 1. I 878 (NY) (unsigned) (0.7 mile), 2. I 315 (MT) (unsigned) (0.8 mile), 3. I 110 (TX) (0.9 mile)
The only interstates with three of the same digits: I 444 (OK) (unsigned), I 555 (AR)
Interstate loops that do not share any portion of their route with another Interstate: I 610 (TX), I 270 (OH), I 485 (NC), I 295 (FL)
The longest concurrency of three Interstates: I 39, I 90, and I 94 in Wisconsin (29 miles)