The Yokosuka-Yokohama section was designated as National Highway 45 on 8 July 1887 and became National Highway 31 in 1920 and Route 16 in 1952.
The Yokosuka-Yokohama section was identified as National Highway 45 on July 8, 1887, and transformed into National Highway 31 in 1920 and Route 16 in 1952.