What It Means
Load posting is the regulatory process of restricting the maximum vehicle weight permitted on a bridge whose load rating analysis shows it cannot safely carry standard legal loads. When an engineer performs a load rating (typically under the AASHTO Manual for Bridge Evaluation using either Allowable Stress, Load Factor, or Load and Resistance Factor Rating methodology), the rating may reveal that the bridge's Operating or Inventory rating factor is below 1.0 for certain vehicle configurations. In that case the bridge owner must either strengthen the structure, replace it, or post weight restrictions. Posted signs display maximum allowable gross vehicle weights, often separately for single-unit trucks, combination vehicles (tractor-trailers), and specialized configurations. Posting status is recorded in NBI Item 41 (Structure Open, Posted, or Closed). Approximately 13% of U.S. bridges are currently posted or closed, with rates substantially higher on rural county-owned bridges where older, lighter-design structures are common. Load posting has significant economic consequences: commercial carriers must detour around posted bridges, school buses and emergency vehicles may need alternate routes, and agricultural operations can be cut off from markets. A 2019 study by the American Road & Transportation Builders Association estimated that heavy truck detours around posted bridges add millions of miles annually in the Midwest alone. Bridges are re-rated when condition changes materially, so a bridge may become posted following a deterioration-driven downgrade, or posting may be lifted after rehabilitation. The Bridge Formula established under the 1982 Surface Transportation Assistance Act sets the federal baseline for legal truck weights that posting thresholds are measured against.
Load Posting is one of the bridge-engineering or FHWA-policy concepts that recurs across BridgeSafety. Below is how the concept connects to the National Bridge Inventory data behind every page on the site.
Within the BridgeSafety Condition Score, each primary component (deck, superstructure, substructure) contributes about a third of the rating, with an age penalty applied to bridges past their typical design life. The methodology page describes the scoring in full detail.
Frequently Asked Questions
What does "Load Posting" mean?
A weight restriction placed on a bridge when its load-carrying capacity falls below standard legal loads, recorded as NBI Item 41.
Why does Load Posting matter for bridge safety?
Load posting is the regulatory process of restricting the maximum vehicle weight permitted on a bridge whose load rating analysis shows it cannot safely carry standard legal loads. When an engineer performs a load rating (typically under the AASHTO Manual for Bridge Evaluation using either Allowable...