 In addition to its inter-city services, Amtrak also operates commuter services for three state agencies including MARC in Maryland, Shore Line East in Connecticut, and Metrolink in California.Service on the Northeast Corridor, between Boston, and Washington, D.C., as well as between Philadelphia and Harrisburg, is powered by overhead electric wires; for the rest of the system, diesel locomotives are used.Routes vary widely in frequency of service, from three-days-a-week trains on the "Sunset Limited" to weekday service several times per hour on the Northeast Corridor (NEC).