The Environmental Protection Agency has issued a proposed rulemaking to change the certification requirements for natural gas vehicle aftermarket conversions.

Under the proposed rulemaking, the agency would approve systems for use on vehicles older than two years, but would not require the Certificate of Conformity for these vehicles. In addition, the agency has also proposed three potential options for engines that have exceeded their regulatory useful life.

NGVAmerica, an organization that promotes the use of natural gas or biomethane, spoke out in support of the agency's move, saying the current regulations are too restrictive.

"Until there are sufficient numbers of original equipment manufacturers' products available in the marketplace, our industry will continue to need aftermarket conversions to help us grow, to help us justify the necessary investments in fueling stations, and to help us increase market penetration," said Jeff Clarke, general counsel and director of regulatory affairs for NGVAmerica. "Conversions fill a void unmet by original equipment manufacturers and demonstrate consumer demand for new applications. Conversions also provide a ready means of addressing the emissions and fuel consumption of medium and heavy duty vehicles that will continue to be in operation for many years to come."

During a hearing on the proposed rule changes, Clarke said the EPA should state that converting a vehicle does not void the original equipment manufacturers warranty. The change should also allow aftermarket manufacturers to pay the certification fees at the end of each quarter or annually based on the total number of vehicles sold, rather than based on expected sales. NGVAmerica also recommended the agency specifically state that manufacturers can seek both a Certificate of Conformity for the new vehicle and approval for converting this vehicle after two years. Clarke also said manufacturers should be able to use chassis testing that has been approved by EPA.