H.R. 5321 extends a federal program that allows electric vehicles and other low-emission vehicles to use high-occupancy vehicle (HOV) lanes, commonly known as carpool lanes. The bill pushes back the expiration date of this exemption from September 30, 2025 to December 31, 2026, giving the program an additional 15 months to operate. The legislation also requires the Secretary of Transportation to conduct and report back to Congress within 180 days on how effective these electric vehicle exemptions are at reducing traffic congestion. This bill affects electric vehicle owners who currently benefit from HOV lane access and the states and local jurisdictions that manage these lanes. The bill contains no specific funding allocations but extends an existing program at no apparent new cost.