On November 15, 2013, FHWA delivered a memo to require that all bridges be load rated for Specialized Hauling Vehicles (SHVs) as defined in the current AASHTO

Manual for Bridge Evaluation (MBE)

and load restricted if necessary. These single unit trucks have multiple axles that are closely spaced and moveable axles that raise or lower if needed, resulting in higher concentrated loads within the shorter axle spacing. The MBE defines 4 SHV trucks: SU4, SU5, SU6, SU7 and one Notional Rating Load (NRL). The Notional Rating Load, NRL, may be used as a screening load model for single-unit trucks that meet Formula B. Bridges that result in RF ≥ 1.00 for the NRL loading will have adequate load capacity for all legal single-unit Formula B truck configurations up to 80,000 lbs. Figure 6-3 shows the detailed load configurations for these load rating trucks. When SHV load ratings are performed, present them to the State in Operating Rating factors. TxDOT has compiled a guide to the load rating of structures for SHVs, available on the Bridge Division webpage.