U.S. Route 101 - Numbering

Numbering

According to the AASHTO's numbering scheme for U.S. Highways, three-digit route numbers are generally subsidiaries of two-digit routes. However, the principal north–south routes were assigned numbers ending in 1. Rather than lose four available north–south numbers (93, 95, 97, and 99) or assign the primary west coast highway a "lesser" number, the AASHTO made an exception to its two-digit rule. Thus, U.S. 101 is treated as a primary, two-digit route with a "first digit" of 10, rather than a spur of U.S. 1. Thus U.S. Route 101, not U.S. 99, is the westernmost north–south route in the U.S. Highway system.