A detour or diversion route is a route around a planned area of prohibited or reduced access, such as a construction site. Standard operating procedure for many roads departments is to route any detour over roads within the same jurisdiction as the road with the obstructed area.
On multi-lane highways (e.g. freeways, expressways, city streets, etc.), usually traffic shifts can be utilized in lieu of a detour as turn lanes can often be congested with detours.
Read more about Detour: Permanently Signed Detour Routes