Risk-Based Weight Restrictions
To preserve bridge safety, PennDOT updated the state's criteria at which bridges are posted with weight restrictions.
Bridges are designed to carry loads above the weights of fully loaded tractor trailers (80,000 pounds). Bridge engineers call this ability to carry weights in excess of 80,000 pounds a factor of safety. The American Association of State Highway Transportation Officials (AASHTO) has bridge weight-limit postiing criteria ranging anywhere between where that factor of safety starts to decline all the way down to where the bridge has lost about half of its factor of safety.
Bridges that have lost half of their factors of safety are still safe and can remain open with no posting. However, their deterioration will be accelerated. Without sufficient revenue, PennDOT will be forced to curtail bridge repairs, meaning bridges that were not posted because they were scheduled for repairs would now be added to the posted list since the money is no longer available to restore them back to that acceptable factor of safety.