Transport programs provide a means for the Environmental Protection Agency to regulate states’ emissions that endanger human health in neighboring areas. The Clean Air Interstate Rule and the Cross-State Air Pollution Rule are transport programs implemented under the authority of the good neighbor provision. However, the Court of Appeals for the District of Columbia Circuit remanded the Clean Air Interstate Rule without vacatur in December 2008, citing statutory infirmities. The court also vacated the Cross-State Air Pollution Rule in August 2012, citing improper reliance on the good neighbor provision. Now it is unclear whether the Environmental Protection Agency can create a new transport program in accordance with the court’s interpretation of the good neighbor provision. It is also unclear how grandfathering of sources and fuel switching might play a future role in emissions reductions.