A detour or (British English: diversion) is a (normally temporary) route taking traffic around an area of prohibited or reduced access, such as a construction site. Detours must be followed and failure to do so may result in fines. 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.
References
Detour Wikipedia(Text) CC BY-SA