What is the largest US highway?

US Highway 1. The first leg originaly ran from St Augustine to what is now Jacksonvill. Today it runs from Du val St in Keywest. all the way to the Canadian border. Where it runs from Key Weat through Monroe county, it is the only road, all other roads are named streets! What can you expect in Mono: one. Roe; road. county!

Actually Arizona Route 88 is older. Open in 1904 prior to Arizona becoming a state it is also know as the Apache Trail