Code of Federal Regulations Title 40. Protection of Environment § 40.92.603 General provisions

(1) Manufacturers and remanufacturers shall test one locomotive engine family each year for which it has received a certificate of conformity from EPA. Where a manufacturer holds certificates of conformity for both freshly manufactured and remanufactured locomotive engine families, the Administrator may require the manufacturer to test one freshly manufactured engine family and one remanufactured engine family. The Administrator may require a manufacturer or remanufacturer to test additional engine families if he/she has reason to believe that locomotives in an engine family do not comply with emission standards in use.

(2) For engine families of less than 10 locomotives per year, no in-use testing will be required, unless the Administrator has reason to believe that those engine families are not complying with the applicable emission standards in use.