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 provide additional time for compliance with these emissions standards, reflecting concerns from stakeholders about the readiness of the industry to meet the original timeline. By postponing the requirements, the bill aims to balance environmental goals with the practical capabilities of manufacturers and operators of heavy trucks.