A portal near the span was damaged by a truck on Monday.
Thurmont, Md (KM) Roddy Road near the historic covered bridge north of Thurmont has been closed. The Frederick County Office of Highway Operations says a truck struck a warning portal south of the bridge on Monday afternoon.
The span itself was not damaged as the portal stopped the vehicle from crossing.
Officials say repairs are expected to be completed before the end of the week.
Motorists who normally travel that area are urged to find an alternate route. The Division of Fire and Rescue Services and the school system have been notified.
By Kevin McManus