The Massachusetts commuter rail network includes both electrified and non-electrified lines. The NSRL tunnels will be fully electrified with an overhead high-voltage catenary system. Because the diesel locomotives that currently serve the non-electrified portions of our system cannot operate in tunnels, and are unable to use the catenary power system, "Dual Mode" locomotives that are able to run on both power sources will be used. Versions of this equipment have been operating for many years in New York, and a new generation of dual mode locomotives is operating successfully in Montreal and New Jersey. This equipment provides excellent performance and operating flexibility in a hybrid system like ours, where electrification may be phased in over time.