Using the Bureau of Transport and Communications Economics' Road Infrastructure Assessment Model (RIAM), the Roads 2020 study makes forecasts at a strategic level of expenditure needs for investment and maintenance between 1998 and 2005 and between 2005 and 2020. It also indicates the locations and types of these expenditures. The forecasts cover non-urban roads and bridges which are either part of the National Highway System or are considered to be of national significance by the States and Territories. Expenditures predicted are upgrading road capacity (widening, adding lanes), town bypasses, maintenance, and bridge replacement. Some types of investment have been omitted because of data deficiencies or modelling difficulties. The exclusions are urban roads, flood mitigation projects, major realignment projects and widening roads used by road trains for safety reasons. Investments justified on social or equity grounds are also excluded. Traffic levels were forecast using population projections and origin-destination data. Total forecast expenditure needs for the National Highway System for the coming 22 year period have been estimated at $16.8 billion of which the backlog comprises $2.6 billion.