California State Route 256 was a never constructed western bypass of downtown Roseville of Placer County. California State Route 256 was created via 1965 Legislative Chapter 1372 and appears to have been a conceptual replacement for what was US Route 99E. The adopted routing of California State Route 256 was dropped in 1976 and it was deleted by the State Legislature during 1994.
https://www.gribblenation.org/2022/08/unbuilt-california-state-route-256.html?m=1