Juneau, Alaska, is unique among U.S. state capitals in that there are no roads connecting the city to the rest of the state or to the contiguous United States. Honolulu, Hawaii, is the only other state capital that is not connected by road to the contiguous United States. The absence of a road network is due to the extremely rugged terrain surrounding the city. In turn, Juneau is a de facto island city in terms of transportation; all goods coming in and out must be transported by plane or boat despite the city's location on the Alaskan mainland.

Source: Wikipedia