The Altamont Corridor 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. The 86-mile (138 km) route includes ten stops, with travel time about 2 hours and 12 minutes end-to-end. In 2023, the line had a ridership of 576,300, or about 2,500 per weekday as of the fourth quarter of 2023. ACE uses Bombardier BiLevel Coaches, MPI F40PH-3C locomotives, and Siemens Charger locomotives.