Interstate 390

Interstate 390 is an east–west auxiliary Interstate Higwhay spur of Interstate 90, situated in eastern Poland. It's westernmost terminus is at I-90 in Warsaw, and it's easternmost terminus is at PO-8 near Białystok.

I-390 serves as a connection with Poland's capital, Warsaw, with Białystok, the county seat and largest city in Bialystok County.

It is currently the longest auxiliary Interstate Highway in the Interstate Highway System. I-801 was intended to surpass I-390's length with an estimated 144 miles, but the 51-mile section of that highway was replaced with the realignment of I-26 between Porto and its northern terminus.