Background:
The transportation community relies on vehicle-based measures to characterize highway demands. The two most common and widely adopted standards are the annual average daily traffic (AADT) and the annual average daily truck traffic (AADTT). While such vehicle-based measurements provide highly effective assessments for highway planning, construction, operations, and maintenance, gaps exist in the number of persons traveling in a vehicle, and the tonnage and dollar values of freight moved on trucks.
On the freight front, efforts such as the truck weigh-in-motion program and the Vehicle Inventory and Use Survey (VIUS) at the national level have been providing information to link truck flow data to the tonnage and dollar values of goods moved. On the passenger travel front, the National Household Travel Survey (NHTS), along with limited state and local surveys, offer a glimpse of vehicle occupancy information. Unfortunately, the current household survey data are not robust enough in deciphering more disaggregated strata such as time of day, seasonality, geographical area, and roadway types regarding vehicle occupancy.