The NBI number is a 15-digit number or alpha-numeric string that uniquely identifies each bridge and typically contains information about the location of the bridge. This may also be referred to as a bridge’s structure ID or permanent structure number (PSN). NBI numbers must be unique to each structure; they cannot be changed after a bridge is added to the inventory, nor can they be reused when a bride is replaced. Bridges that are being widened or rehabilitated retain their PSNs.

The assignment of NBI numbers for new and replacement structures depends on whether the bridge is on-system or off-system.