The Transportation Equity Act for the 21st Century (TEA-21) authorized $217.9 billion for highway, mass transit, and other surface transportation programs for fiscal years 1998 through 2003. TEA-21 continued the use of the Highway Trust Fund -- which is divided into a Highway Account and a Mass Transit Account -- as the mechanism to account for federal highway user tax receipts that fund various surface transportation programs. Highway user taxes include excise taxes on motor fuels (gasoline, gasohol, diesel, and special fuels) and truck-related taxes on truck tires, sales of trucks and trailers, and the use of heavy vehicles. TEA-21 also established mechanisms for ensuring that the level of federal highway program funds distributed to the states would be more closely linked than before to the highway user tax receipts credited to the Highway Account of the Highway Trust Fund.2 The process for distributing these tax receipts has two separate components: (1) the Treasury Department determines the overall amount of receipts in the Highway Account and (2) the Federal Highway Administration (FHWA) estimates the portion of the overall amount that is attributable to each state by using state data on motor fuel usage. Under TEA-21, billions of dollars in highway program funds, about $13 billion in fiscal year 2000 alone, are distributed to the states on the basis of information developed by the Treasury and Transportation departments. Given the increased linkage between Highway Account receipts and the level of highway program funds distributed to the states and the magnitude of the dollars involved, effective processes for collecting and reporting accurate information on such receipts are critical to the effective implementation of TEA-21. This report discusses (1) the Treasury Department's process for allocating highway user tax receipts to the Highway Account of the Fund, (2) FHWA's process for estimating motor fuel usage and the contributions to the account that are at