Highway Funding Equity Act of 2003 - Revises Federal highway funding minimum guarantee provisions. Requires the Secretary of Transportation, for each of FY 2004 through 2009, to allocate among the States amounts sufficient to ensure that the percentage for each State of the total apportionments for the fiscal year for the National Highway System (NHS), the high priority projects program, the Interstate maintenance program, the surface transportation program, metropolitan planning, the highway bridge replacement and rehabilitation program, the congestion mitigation and air quality improvement program, the recreational trails program, the Appalachian development highway system, and the minimum guarantee equals or exceeds 95 percent of the ratio that the estimated tax payments to the Highway Trust Fund (HTF) (other than the Mass Transit Account) attributable to highway users in the State bears to such payments attributable to highway users in all States (with a specified exception for any State having a population density of less than 50 individuals per square mile).
Sets forth provisions regarding: (1) the programmatic distribution of NHS funds exceeding $2.8 billion; (2) the apportionment of the remainder of funds to the States; and (3) required adjustments where the sum of State percentages exceeds 100.