Altamont Corridor Express (ACE)
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| Altamont Corridor Express (ACE) | |
|---|---|
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| Name | Altamont Corridor Express |
| Locale | Northern California |
| Type | Commuter rail |
| Status | Operating |
| First | 1998 |
| Operator | San Joaquin Regional Rail Commission |
| Stock | Diesel-electric locomotives; bilevel coaches |
| Line length | ~86 miles |
Altamont Corridor Express (ACE) Altamont Corridor Express is a commuter rail service in Northern California connecting San Joaquin County, Alameda County, and Santa Clara County. The service links suburban and exurban communities with employment centers in San Jose, California, providing weekday and limited weekend service that integrates with regional systems like Bay Area Rapid Transit, Caltrain, and Amtrak. Founded to relieve highway congestion on Interstate 580 and Interstate 680, the agency operates under the governance of the San Joaquin Regional Rail Commission.
Overview
ACE operates on a corridor that traverses the Altamont Pass and follows rights-of-way historically associated with the Southern Pacific Railroad and Atchison, Topeka and Santa Fe Railway. The service connects terminals in Stockton, California and San Jose, California, with intermediate stops in communities such as Tracy, California, Livermore, California, Pleasanton, Fremont, California, and Santa Clara, California. ACE coordinates transfers with agencies including Valley Transportation Authority (Santa Clara County), San Joaquin Regional Transit District, and Union Pacific Railroad which owns portions of the track.
History
Planning for commuter rail across the Altamont Pass followed decades of studies involving transit agencies and regional planning bodies like the Metropolitan Transportation Commission and Association of Bay Area Governments. The inaugural ACE service began in 1998, after capital funding and operating agreements were established among local governments, the California Department of Transportation programs, and federal grants administered by entities such as the Federal Transit Administration. Early operations used leased equipment and trackage rights negotiated with Union Pacific Railroad and successor freight operators. Expansion of frequencies, stations, and rolling stock occurred through the 2000s and 2010s amid debates over alignment, grade separations, and environmental review processes overseen by the California Environmental Protection Agency-linked review frameworks.
Operations and Services
ACE provides peak-direction commuter service oriented to weekday travel, with schedules timed to serve employment markets in Downtown San Jose and the San Joaquin County employment bases. Trains operate using diesel locomotives with push-pull bilevel coaches, integrating ticketing and connections with regional systems such as Amtrak Thruway Motorcoach, Capitol Corridor, and VTA Light Rail. Operations require coordination with freight movements belonging to Union Pacific Railroad and regulatory oversight from the Federal Railroad Administration. Service features include reserved seating policies during peak periods, bicycle accommodations consistent with Caltrain practice, and station amenities governed by local transit district standards.
Rolling Stock and Equipment
ACE rolling stock has included rebuilt EMD F40PH and F59PH diesel-electric locomotives, as well as newer Tier 4-compliant units procured for emissions reduction in line with California Air Resources Board guidelines. Passenger consists primarily use bilevel commuter coaches from manufacturers like Bombardier Transportation and Stadler Rail, rebuilt to ACE specifications. Maintenance and heavy overhaul are performed at facilities located in Stockton, California and satellite shops near San Jose Diridon Station. Onboard systems have been upgraded periodically to include Positive Train Control equipment meeting Railroad Safety Improvement Act requirements and Federal safety standards.
Stations and Route
The ACE corridor runs roughly east–west across the northern San Francisco Bay Area periphery, traversing the Altamont Pass corridor and linking the southern San Joaquin Valley with the Silicon Valley employment center. Principal stations include Stockton – San Joaquin Street, Lathrop/Manteca, Tracy ACE Station, Livermore, Pleasanton (shared vicinity with BART), Fremont Centerville, Great America, and San Jose Diridon Station. Several stations are intermodal hubs connecting to Amtrak California services, local bus networks, and regional rail projects. Infrastructure along the route requires ongoing investments in grade separations, signaling, and track rehabilitation in partnership with freight owners.
Ridership and Performance
Ridership on ACE has reflected regional commuting patterns, showing increases during economic expansions and declines during downturns, with measurable impacts from events such as the COVID-19 pandemic. Performance metrics tracked by the San Joaquin Regional Rail Commission include on-time performance, average trip times, farebox recovery, and passenger counts correlated to regional employment indicators from Santa Clara County Office of Economic Development and San Joaquin County Economic Development Association. ACE publishes periodic service reports and participates in regional transit studies conducted by the Metropolitan Transportation Commission and California State Transportation Agency.
Future Expansion and Projects
Planned expansions include increased frequencies, electrification studies, and extensions under the broader Valley Rail program and state-supported initiatives such as the California State Rail Plan. Projects under study or development involve new stations in Ceres, Modesto, and other San Joaquin County nodes, further integration with BART Silicon Valley expansion and connections to High-Speed Rail planning corridors. Funding sources combine state transit grants, federal infrastructure programs, local sales tax measures, and partnerships with freight owners like Union Pacific Railroad. Long-term visions include enhanced corridor capacity through double-tracking, additional grade separations, and potential transition to zero-emission propulsion technologies in compliance with California Air Resources Board mandates.