H.503 is a bill introduced by a group of representatives aimed at delaying the implementation of the Advanced Clean Truck rule by five years. This rule, which is designed to regulate emissions from heavy trucks, would now apply starting with model year 2036 instead of the previously established model year 2031.

The bill seeks to amend current law regarding air pollution control and motor vehicle emissions, specifically targeting the requirements for heavy trucks. By postponing the rule's requirements, the bill reflects a legislative intent to provide additional time for compliance and adaptation within the trucking industry.