Arizona House Bill 2292, which passed in the Spring 2003 session of the Arizona Legislature, established the Maricopa Association of Governments (MAG) Transportation Policy Committee (TPC). Tasked with developing a Regional Transportation Plan (RTP) for Maricopa County they established the process for an election to extend the current half-cent County Transportation Excise Tax. On Novemeber 2, 2004 voters in Maricopa County approved Proposition 400 to extend the half-cent sales tax for transportation for an additional twenty years to 2026. The extension began Jauuary 1, 2006 and ends on December 31, 2025.

In accordance with ARS §42-6105.E, 56.2 percent of the Proposition 400 sales tax collections are distributed to freeways and state highways; 10.5 percent are distributed to arterial street improvements and 33.3 percent are distributed to the public transportation fund. The Regional Transportation Plan thus has three major components; Freeways/Highwys, Transite and Arterial Roads.

The RTPFP includes new freeway corridors to serve growth in the region and improvements to the existing system of freeways and highways to reduce current and future congestion and improve safety. The work includes new freeway corridors, additional lanes on existing facilitie and new interchanges at arterial cross streets, high occupancy vehicle ramps at system interchanges, noise mitigation, litter and landscape maintenance programs, freeway management systems and freeway service patrols. The RTPFP is funded by three primary revenue sources; Proposition 400 half-cent sales tax, ADOT funds dedicated to use in Maricopa County, and federal highway funds.