The truck factor characterizes the average number of ESALs per truck. FHWA’s Traffic Monitoring Guide (TMG) provides guidance on such characterizations. Vehicles such as motorcycles, passenger cars, vans and pickup trucks have negligible impact on the truck factor. Buses can truck factors ranging from 0.57 ESALs/bus for a typical-length, empty bus to up to 6.17 ESALs/bus for articulated buses with all seats filled and standing passengers. Similarly, the truck factor for trucks can have a very large range, depending on configuration and weight restrictions. The default value of 1.7 ESALs/truck may be used for typical bus and truck traffic loadings unless another value is locally available.