Interstate Trivia & Records

• The Interstate Highway shield was designed by Richard Oliver of Texas as a black and white shield; the red, white, and blue version was approved by the American Association of State Highway Officials (AASHO) in 1957. It is trademarked.
• The Federal-Aid Highway Act and Department of Transportation Act passed by Congress in 1966 mandated that all Interstates be four lanes. Previously daily traffic counts determined whether an Interstate would be two or four lanes.¹
• Four state capitals are not served by the Interstate Highway System as of 2006: Juneau, Alaska; Dover, Delaware; Jefferson City, Missouri; and Pierre, South Dakota.
• It is not true that one mile of every five miles of Interstate highway must be straight enough to allow planes to land on it. This is an urban legend.
• Previously with one exception (I-65), Interstate 64 overlaps with every two-digit interstate it meets from Wentzville, Missouri to Hampton Roads, Virginia. I-64 overlaps with I-55, I-57, I-71, I-75, I-77, I-81 and I-95. Prior to 2014, I-64 also overlapped with I-70 between St. Louis, Missouri and East St. Louis, Illinois.

Highest/Lowest Points on System

• Highest Point: Interstate 70 at Eisenhower Tunnel in Colorado, 11,192 feet above sea level
• Lowest Point (excluding tunnels): Interstate 8 near El Centro in California, approximately 52 feet below sea level

Shortest Routes:

• I-878 New York - shortest unsigned route
• I-375 Michigan - shortest signed route

Longest Routes:

• I-90
• I-80
• I-40
• I-70
• I-10

Routes with unusual numbering

Interstate 238 in California is designated despite there being no Interstate 38. That is because the link between I-880 and I-580 was previously designated as part of California State Route 238. Since no other branches of I-80 were available for use, it was simply upgraded directly to I-238.

The Interstate 69 suffixes in South Texas were written into law by an act of Congress. Interstate 87 in North Carolina, which generally travels west to east, has an odd number. I-87 replaced Interstate 495 as the proposed designation between I-95 and Raleigh. The North Carolina Department of Transportation signed I-495 as with north / south cardinal directions with respect to Interstate 95.

References:

1. "Timeline outlines Montana Department of Transportation history." Montana Standard, June 16, 2013.