According to Wikipedia: "The highway originally served as a fork of I-80 to serve the Pacific Northwest, and was originally numbered Interstate 80N. The highway serves and connects Portland, Oregon and Boise, Idaho with Ogden, Utah. Seattle, Washington is indirectly served by I-84 via a connection with Interstate 82. With the connection to I-80, I-84 connects these cities to points east."
Submitted by MrK