Explain the concept of 'legal load rating' and its practical implications.

Legal load rating is the process of determining the maximum load a bridge can carry according to the legal weight limits specified by state or federal regulations. It ensures that bridges can safely accommodate the routine passage of legally loaded vehicles without exceeding allowable stress limits or compromising structural integrity. The legal load rating is typically lower than the operating rating and is used to establish weight restrictions and posting limits for bridges. The practical implications of legal load rating are that it directly affects the types and weights of vehicles that can legally use a bridge. If a bridge's legal load rating is below the standard legal load limit, it must be posted with a weight restriction, limiting the types of vehicles that can cross it and potentially impacting commerce and transportation routes.