Interstate 326 was a designation proposed by the Johnson City Metropolitan Transportation Planning Organization in northeastern Tennessee for the U.S. 321 freeway between I-26/U.S. 19W-23 in Johnson City and Elizabethton. The Interstate 26 Extension
http://www.jcmpo.org/I26ext.htm page on the MTPO web site referenced:
I-326 possible number for US 321 (SR 67) Existing freeway between Johnson City and Elizabethton, TN.
The freeway section of U.S. 321 (Milligan Highway) leads east from a parclo interchange with Interstate 26 in Johnson City to Tennessee State Route 359 (Milligan Highway) in western reaches of Elizabethton. Upgrades were never made to this stretch of highway and no further efforts promoted Interstate status.