I-225  Colorado (link)

12.00 miles [1]; from I-25 to I-70, serving Aurora (near Denver). Finished around 1976.

Another declined letter-suffix interstate: 25E

The Colorado Department of Highways originally proposed the number I-25E for what is now I-225 and I-270; in 1958 AASHTO turned it down. [2] New letter-suffixed interstates are prohibited now, and almost all existing ones have been renumbered. Even in the late 1950s, AASHTO was discouraging a practice that was common with U.S. numbered routes.

Other letter-suffix proposals include I-59B (today's I-459), I-95E (I-195, Providence), and I-63N (I-695, D. C.).

The only letter-suffix interstate remaining: I-35E/W, in Dallas-Fort Worth and Minneapolis-St. Paul.

225 once proposed for C[I]-470

On Dec. 13, 1968, as part of that year's Federal Aid Highway Act, the FHWA approved an extension of I-225 for a southwestern Denver bypass. On May 2, 1969, this was renumbered to I-470; but in the mid-1970s, I-470 was cancelled, and on Sept. 20, 1977, the number was withdrawn.

See also:

• I-225 (AARoads)
• Other Colorado 3di's: I-270, cancelled I-470
• Interstate system route numbering (Stephen Summers; FHWA and AASHTO info)

I-425 (numbered as another interstate)  Colorado (link)

Interstate 425 was a late 1950s proposal for what is now I-270 and I-76, from I-70 to I-25 in northeastern metro Denver. On Feb. 26, 1959, I-425 was shorted and renumbered I-270, and I-76 (formerly I-80S) was extended. [2]

Sources

1. Route Log and Finder List - Interstate Highways, FHWA, Oct. 31, 2002.
2. Summers, Stephen. "Interstate Numbering aashto AASHTO & fhwa fhwa." Online posting, misc.transport.road, April 18, 2003.