In recent years, requests to move heavy vehicles across bridges have risen dramatically. Highway agencies find it necessary to calculate safety margins under loads significantly above legal levels. For some regions of the U.S., permits have effectively raised the legal vehicle weight. Reliability analysis is used in this study to model live load uncertainties (using bridge weigh-in-motion data) and other dead load and resistance variables. Target safety indices are introduced by calibration with existing bridge rating and posting practices. Simulation of the expected maximum load effects of permit vehicles plus alongside vehicles has been carried out for both frequent permits, for different traffic classifications including volume and traffic enforcement levels, and single passage permits. Load factors are calibrated to achieve the target safety indices for different simple and continuous spans. A checking format for permit vehicles is proposed for possible inclusion in a bridge evaluation code. For the covering abstract of the Conference see IRRD Abstract No. 807839.