Altamont Corridor Express

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.[4] Service is managed by the San Joaquin Regional Rail Commission, and operations are contracted to Herzog Transit Services, using AAR assigned reporting mark ACEX.[4][5] The 86-mile (138 km) route includes ten stops, with travel time about 2 hours and 12 minutes end-to-end. The tracks are owned by Union Pacific Railroad. ACE uses Bombardier BiLevel Coaches and MPI F40PH-3C locomotives.

Altamont Corridor Express
ACE train traversing Altamont Pass Road while climbing Altamont Pass
OwnerSan Joaquin Regional Rail Commission
Area servedSan Joaquin Valley, Tri-Valley, and Silicon Valley
Transit typeCommuter rail
Number of lines1
Number of stations10
Daily ridership5,900 (weekdays)[1]
Annual ridership1.3 million (2017)[2]
HeadquartersRobert J. Cabral Station
Began operationOctober 19, 1998 (October 19, 1998)[3]
Operator(s)Herzog Transit Services
Reporting marksACEX
Host railroadsUnion Pacific (Stockton–Santa Clara)
Caltrain (Santa Clara–San Jose)
Charactershared freight railroad
Number of vehicles6 locomotives
30 passenger cars
Train length1-2 locomotives
4-8 passenger cars
System length85 mi (137 km)
Track gauge4 ft 8 12 in (1,435 mm) standard gauge
Average speed39 mph (63 km/h)
Top speed79 mph (127 km/h)
System map

Valley Rail
Valley Rail
Old North Sacramento
Midtown Sacramento
City College
Elk Grove
ACE service facility
ACEforward (2023/2027)
ACEforward (2023/2027)
North Lathrop
Phase 1 (2023)
Phase 2 (2027)
San Joaquin County
Alameda County
Vasco Road
Amtrak to Oakland & Seattle
Santa Clara – Great America
Santa Clara
San Jose
Caltrain to Tamien
Amtrak Coast Starlight to Los Angeles

Service began on October 19, 1998, with two weekday round trips. A third round trip was added in May 2001, followed by a fourth round trip in October 2012. Saturday service commenced in September 2019. As of 2018, average weekday ridership is 5,900.[1] Under the ACEforward program, a number of improvements to the service are being considered. These include a rerouted line through Tracy, an extension to Modesto and Merced, and connections to BART at Union City and Tri-Valley.

History and funding


By the 1980s, three rapidly growing areas in California - Silicon Valley, the Tri-Valley, and the middle part of the Central Valley - were poorly connected by public transit, even as Interstate 580 and Interstate 680 became more congested. The three areas had connections to San Francisco and Oakland via Caltrain and the Amtrak San Joaquin (and later BART and Capitol Corridor trains), but commuting from the Central Valley and Tri-Valley to Silicon Valley required using a car or limited bus service. In 1989, the San Joaquin Council of Governments, Stockton Chamber of Commerce, and the Building Industry Association of the Delta started work on a 20-year transportation plan for their section of the Central Valley. In November 1990, San Joaquin County voters passed Measure K, a half-cent sales tax to fund a variety of transportation improvements.[6][7] The highest-priority project was the establishment of passenger rail service to San Jose.[3]

In 1995, San Joaquin County and seven cities along the route formed the San Joaquin Regional Rail Commission (SJRRC) to oversee the creation of the service.[3] In May 1997, the Altamont Commuter Express Joint Powers Authority (ACE JPA) was formed by the SJRRC, Santa Clara Valley Transportation Authority (VTA), and Alameda Congestion Management Agency (ACMA). That agreement formalized financial support, administrative processes, and governance for the rail service.[3] The operation is funded by a variety of state and federal sources, largely sales tax revenue collected by the three JPA signatories; farebox revenues account for about one-third of costs.[8]

Cost sharing for capital projects, excluding stations, during the initial 36 months of service was determined by the JPA on a case-by-case basis and approved by each of the member agencies. The initial purchase of rolling stock, construction of stations, and other start-up costs, amounting to some $48 million, were covered primarily by Measure K funds. Station improvements are the responsibility of the county in which the station is located. ACE pays the owner of the right of way, Union Pacific Railroad, about $1.5 million per year; it also uses about 4 miles (6.4 km) of Caltrain track in San Jose.[9] Service began on October 19, 1998, with two daily round trips running to San Jose in the morning and Stockton in the evening.[6]

Service expansion

The original service used two trainsets, each with 4 bilevel coach cars, for a total seated capacity of 1120 passengers in each direction daily. In September 1999, the service reached 1000 daily riders per direction, resulting in many trains running at capacity.[10] On February 21, 2000, a morning short turn between San Jose and Pleasanton was added using an existing trainset, giving Pleasanton and Fremont a third inbound train to alleviate the crowding on the two earlier trains.[11] The trip was added after ACE funded $3 million in track improvements to reduce conflicts with Union Pacific freight trains and Amtrak Capitol Corridor trains.[12] By early 2001, ACE regularly carried more than 700 daily standees.[13] After additional equipment was bought, the "Turn-back Train" was replaced by a nearly-full-length trip originating at Lathrop-Manteca on March 5, 2001; trains also began stopping at Santa Clara station.[14] Although the third train added 560 seats in each direction, it brought an immediate increase in 380 daily riders. ACE then planned to add a fourth round trip later in the year, with fifth and sixth round trips by 2006.[13] However, by late 2001, the deepening dot-com recession was severely hurting ridership, and expansion plans were put on hold. On June 30, 2003, the ACE JPA was dissolved in favor of a Cooperative Services Agreement between the three member agencies.[3]

On January 6, 2003, ACE introduced the Stockton Solution Shuttle, allowing Stockton passengers to use the ACE trip which terminated at Lathrop/Manteca.[10] The trip was extended to Stockton on August 1, 2005. At that time, service to Santa Clara was suspended to allow for the construction of a second platform and pedestrian tunnel at the station.[15] At this time, three Amtrak Thruway Motorcoach trips connecting to the San Joaquin - one to San Jose and two to Stockton - were open to ACE riders.[10]

On August 28, 2006, ACE added a fourth round trip, which operated midday using one of the existing trainsets.[3] On November 7, 2006, San Joaquin County voters approved a 20-year extension of Measure K.[7] Suffering from reducing funding due to the Great Recession, ACE cut the lightly-used midday trip on November 2, 2009.[10]

Altamont Corridor Express

In May 2012, ACE restored service to Santa Clara station.[6] On October 1, 2012, a fourth rush-hour round trip was added, running approximately one hour after existing trips.[10] In December 2012, the service was rebranded from Altamont Commuter Express to Altamont Corridor Express to reflect plans for a broader scope of service.[16]

In March 2014, ACE opened a $65 million, 121,000-square-foot (11,200 m2) maintenance facility in Stockton.[17] On July 1, 2015, management and governance of the San Joaquin passed from Caltrans to the new San Joaquin Joint Powers Authority.[18] The SJJPA has nominal control over the SJRRC, but delegates all responsibility over ACE to the SJRRC.

On March 7, 2016, an ACE train was derailed by a mudslide in Niles Canyon near Sunol. The front car plunged into the rain-swollen Alameda Creek. Fourteen passengers were injured, but there were no fatalities.[19][20]

ACE received Road Repair and Accountability Act funds in order to initiate Saturday service in January 2018,[21] with two Saturday round trips added in September 2019.

Future plans

In association with the California High-Speed Rail (CAHSR) project, the ACE system had been planned to be dramatically upgraded and expanded. Beginning around 2008, initial plans called for the Altamont Corridor Rail Project to produce a high speed rail "Super ACE" capable of halving the travel time between the endpoints.[25]

As the CAHSR project was scaled back and rerouted to Pacheco Pass several years later, these plans were replaced with the more modest ACEforward program. The San Joaquin Regional Rail Commission issued a notice of intent to proceed with an Environmental Impact Statement in June 2013;[26] this was released in 2017 and prioritized goals as either long term or short term.[2] Short term goals included track improvements, a possible reroute through downtown Tracy including new stations, a West Tracy station, and a new extension to Modesto in addition to additional daily round trips. Long term goals included upgrades to the existing corridor to allow as many as 10 daily round trips, extension to Merced, tunnels under Altamont Pass,[27] and electrification of the line from Stockton to San Jose.[2]

Also to be studied were possible connections with BART at Union City or Livermore[28][29] via traditional ACE rail, diesel multiple units, or bus bridges.[27] This connection is likely to be facilitated by the Tri-Valley-San Joaquin Valley Regional Rail Authority.

The state senate allocated $400 million in revenue from a gas tax increase to ACEforward expansion.[2] ACE was awarded $500.5 million in April 2018 for expanded service to Ceres and Sacramento[30] to provide more rail service and connections within the Central Valley.[31][32] Service is expected to begin from Ceres by 2023[33] with interim bus bridge service to Merced until that segment of Union Pacific right-of-way is upgraded. Four trains will depart Ceres in the mornings, and one train may make the complete run to San Jose with others transferring passengers at Lathrop.[34]

By 2019, the plan had come to be called the Altamont Corridor Vision, with an expected price of $9.7 billion, allowing ACE to run up to six weekday round trips in 2023 with the goal of ten weekday round trips once additional track infrastructure is completed. ACE and the Tri-Valley-San Joaquin Valley Regional Rail Authority sought funding to construct a shared tunnel under Altamont pass in order to speed service and increase reliability.[35] The Union Pacific right of way between Ceres and Lathrop will be double tracked to facilitate passenger service.[33] As of 2019 platforms are being extended to accommodate longer trains.[36]


As of July 2019, ACE operates four round trips per weekday in the peak rush hour directions – westbound (to San Jose) in the morning and eastbound (to Stockton) in the evening. Trains are scheduled to make the 85-mile (137 km) one-way trip in 2 hours 12 minutes, an average speed of 39 miles per hour (63 km/h).[37]

ACE did not operate on weekends or major holidays until September 7, 2019, when two Saturday round trips were added.[38]


From San Jose to just north of Santa Clara, ACE uses the Caltrain main line (Peninsula Subdivision), shared with Caltrain and Amtrak service. From Santa Clara to Stockton - the majority of the route - ACE runs on Union Pacific Railroad freight lines. From Santa Clara to Newark, ACE uses the Coast Subdivision, then the Niles Subdivision to Niles. From Niles to Stockton, the line uses the Oakland Subdivision.[39][40]

The route runs through Niles Canyon, parallel to the Niles Canyon Railway, Highway 84, and the Hetch Hetchy Aqueduct. The line passes through a 0.75-mile (1.21 km) long tunnel which cuts off one of the canyon's horseshoes. This tunnel was modified from its original configuration to accommodate intermodal double-stack freight trains. However, this left the track in poor condition, reducing speeds from 45 mph (72 km/h) to 25 mph (40 km/h) in the summer and as low as 10 mph (16 km/h) during the rainy season. The San Joaquin Regional Rail Commission plans to rehabilitate the tunnel.[41]

East of Pleasanton and Livermore, the line runs through the Altamont Pass on the original Feather River Route. After crossing the California Aqueduct and the Delta-Mendota Canal into the Central Valley, skirting the southern edge of Tracy. It then turns north between Lathrop and Manteca and runs to Robert J. Cabral Station in Stockton.

Tickets and fares

ACE tickets are available at select stations and on ACE's web site. Distance-based fares are available in one way, round trip, 20 trip, weekly, and monthly passes.

Rolling stock

ACE operates push-pull trains with one to two diesel locomotives and four to eight bilevel coach cars.[9] Trains typically operate with the locomotive(s) leading westbound and the cab car leading eastbound.

MPI F40PH-3C63101-3106
Siemens Charger4To be delivered beginning in December 2019[42]
Bombardier BiLevel Coach213201-3221
Bombardier BiLevel Cab Car93301-33093309 wrecked in Sunol mudslide derailment on March 7, 2016.

See also


  1. "Transit Ridership Report: Second Quarter 2018" (PDF). American Public Transportation Association. August 24, 2018. Archived from the original (PDF) on October 4, 2018. Retrieved December 6, 2018.
  2. "ACE expansion report released". Tracy Press. May 31, 2017. Retrieved June 2, 2017.
  3. "History of ACE". San Joaquin Joint Powers Authority.
  4. Solomon, Brian (2013). North American Railroad Family Trees : An Infographic History of the Industry's Mergers and Evolution. Minneapolis, MN: Voyageur Press. p. 127. ISBN 978-0760344880.
  5. "AAR Railroad Reporting Marks (2015)". Railserve. Retrieved June 28, 2016.
  6. "Altamont Corridor Express (ACE)". BayRail Alliance.
  7. "Measure K". San Joaquin Council of Governments. Archived from the original on September 2, 2016. Retrieved August 29, 2016.
  8. "2014-2015 WORK PROGRAM & BUDGET" (PDF). San Joaquin Regional Rail Commission. June 6, 2014. p. 6.
  9. Van Hattem, Matt (June 30, 2006). "Altamont Commuter Express: The commuter rail service linking San Jose and Stockton, Calif". Trains Magazine. Retrieved August 23, 2006.
  10. Cox, Jeremiah (July 10, 2013). "Altamont Commuter Express on the SubwayNut". Subway Nut.
  11. "History". San Joaquin Regional Rail Commission. Archived from the original on May 11, 2000.
  12. Cabanatuan, Michael (November 16, 1999). "ACE to Add Third Morning Train / Pleasanton-to-San Jose service will begin by Feb. 15". San Francisco Chronicle. Retrieved August 29, 2016.
  13. White, Mike (March 12, 2001). "4th Ace train to bolster the fleet". Press Herald. Archived from the original on November 8, 2001 via San Joaquin Regional Rail Commission.
  14. Bott, Fran (March 1, 2001). "Third ACE train ready to roll". The Record. Archived from the original on November 8, 2001 via San Joaquin Regional Rail Commission.
  15. "Schedule Changes will be effective August 1, 2005" (PDF). San Joaquin Regional Rail Commission. August 1, 2005. Archived from the original (PDF) on November 26, 2005.
  16. "SJRRC Refreshes ACE Brand with new Logo" (Press release). San Joaquin Regional Rail Commission. December 10, 2012 via Mass Transit Magazine.
  17. Rembulat, Vince (March 23, 2014). "ACE opens $65M state-of-art facility". Merced Bulletin. Archived from the original on September 16, 2016. Retrieved August 29, 2016.
  18. Sheehan, Tim (June 26, 2015). "Valley agency takes control of Amtrak San Joaquin trains". Fresno Bee. Retrieved August 29, 2016.
  19. "Fallen Tree Derails Train in California; At Least 9 Injured". New York Times. Retrieved March 8, 2016.
  20. Tucker, Jill; Lyons, Jenna; Cabanatuan, Michael. "14 hurt as commuter train derails -- no ACE service Tuesday". SFGate. Retrieved March 8, 2016.
  21. Wanek-Libman, Mischa (January 31, 2018). "California rail providers receive $52M in state funding". RT&S. Retrieved February 2, 2018.
  22. "Executive Summary" (PDF). ACE Rail. ACE. Retrieved June 2, 2017.
  23. "Chapter 2 2 Description of Phase I Improvements" (PDF). ACErail. ACE. Retrieved April 28, 2018.
  24. "HERE COME THE TRAINS". Manteca Bulletin. April 27, 2018. Retrieved April 28, 2018.
  25. Johnson, Zachary K. (November 13, 2009). "'Super ACE' rail project touted". Modesto Bee. Retrieved August 22, 2016.
  26. "NOTICE OF PREPARATION OF AN ENVIRONMENTAL IMPACT REPORT". San Joaquin Regional Rail Commission. June 24, 2013.
  27. "Executive Summary" (PDF). ACE Rail. ACE. Retrieved June 2, 2017.
  28. "ACEforward Alternatives Analysis and Development (presentation at SJRRC Board Meeting)" (PDF). San Joaquin Regional Rail Commission. April 4, 2014.
  29. "ACEforward – Improving the Altamont Corridor Express" (PDF). San Joaquin Regional Rail Commission. July 2015.
  30. Holland, John (April 27, 2018). "Expanded train service coming to Modesto, Merced; what it means for commuters". Modesto Bee. Retrieved April 28, 2018.
  31. Vaughn, Danielle (February 8, 2017). "San Joaquin rail service plans expansion of Sacramento route". Lodi News-Sentinel. Retrieved February 14, 2017.
  32. "NOTICE OF PREPARATION OF AN ENVIRONMENTAL IMPACT REPORT: ACE Extension Lathrop to Ceres/Merced" (PDF). San Joaquin Regional Rail Commission. January 10, 2018.
  33. Wyatt, Dennis (October 9, 2019). "ACE on track for Manteca & Ripon stops". Manteca Bulletin. Retrieved October 14, 2019.
  34. "ACE Extension Lathrop to Ceres/Merced Draft EIR Executive Summary ES.3.1.2 Operation and Maintenance" (PDF). San Joaquin Regional Rail Commission. Retrieved January 14, 2019.
  35. Holland, John (September 1, 2019). "Forty trains a day through Altamont at up to 125 mph? It could happen, weary drivers". Modesto Bee. Retrieved September 18, 2019.
  36. "SJRRC selects LAN for Altamont Corridor Express Platform Extension Project". Mass Transit. Lockwood, Andrews & Newnam Inc. November 27, 2019. Retrieved December 6, 2019.
  37. "Getting You There". San Joaquin Joint Powers Authority. Retrieved July 2, 2019.
  38. "ACE® SATURDAY SERVICE TO BEGIN SEPT. 7, 2019" (Press release). San Joaquin Joint Powers Authority. August 21, 2019.
  39. "SUPPLEMENTAL NOTICE OF PREPARATION OF AN ENVIRONMENTAL IMPACT REPORT: ACEforward – Notice of Additional Project Element – Niles Junction Connections" (PDF). San Joaquin Regional Rail Commission. May 9, 2016. p. 8.
  40. SMA Rail Consulting (April 2016). "California Passenger Rail NETWORK SCHEMATICS" (PDF). California Department of Transportation.
  41. Luna, Henry J.; The Pacific Locomotive Association (2005). Niles Canyon Railways. Charleston, SC: Arcadia. ISBN 978-0738529837.
  42. "Altamont Corridor Express orders Charger locomotives". Trains Magazine. April 26, 2018. Retrieved April 27, 2018.

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