The Altamont Corridor Express (also known as ACE, formerly Altamont Commuter Express) is a commuter rail service in California, connecting Stockton and San Jose during peak hours only. ACE is named for the Altamont Pass, through which it runs. Service is managed by the San Joaquin Regional Rail Commission, and operations are contracted to Herzog Transit Services, using AAR assigned reporting mark ACEX. The route includes ten stops, with travel time about 2 hours and 12 minutes end-to-end. The tracks are owned by Union Pacific Railroad, previously built along the Western Pacific Railroad main line. ACE uses Bombardier BiLevel Coaches and MPI F40PH-3C locomotives.