On request of any local authority, the State Highway Administration shall investigate and, on its own initiative, it may investigate any bridge or other elevated structure that is a part of a highway. If it determines that the structure cannot safely withstand the weight of vehicles traveling at the maximum speed limit otherwise permitted by this subtitle, the State Highway Administration shall: Establish the maximum speed limit that the structure can safely withstand; and At each approach to the structure, place or permit the placement of a suitable sign stating the maximum speed limit. A maximum speed limit established under this section is effective when posted on appropriate signs giving notice of the limit.