The number of motor vehicles available to a household has a major impact on the travel behavior of the members of the household. As a result, many metropolitan planning organizations have incorporated models of household vehicle availability or automobile ownership into their travel forecasting model systems. This report summarizes the current state of the practice in modeling vehicle availability. In the past, these new models were most frequently labeled auto ownership models, but more recently the term vehicle availability, a measure of the total number of motor vehicles available for use by household members (including both passenger cars and trucks owned, leased, and/or provided by employers), is likely to be more closely related with the level of household mobility than the more limited household auto ownership measure. Secondly, data on vehicle availability is collected in the decennial U.S. Census rather than auto ownership.