Altamont Corridor Express

ACE train at San Jose Diridon station

By the 1980s, three rapidly growing areas in California – Silicon Valley, the Tri-Valley, and the San Joaquin Valley – were poorly connected by public transit, as Interstate 580 and Interstate 680 became more congested. Commuting from the San Joaquin Valley or the 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 the northern section of the San Joaquin Valley. In November 1990, San Joaquin County voters passed Measure K, a half-cent sales tax to fund a variety of transportation improvements.[7][8] The highest-priority project was the establishment of passenger rail service to San Jose.[3]

Former ACE logo, used until 2013

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, while farebox revenues account for about one-third of costs.[9]

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 Union Pacific Railroad about $1.5 million per year to use their tracks. ACE trains also use about 4 miles (6.4 km) of Caltrain track in San Jose.[10] Service began on October 19, 1998, with two daily round trips running to San Jose in the morning and Stockton in the evening.[7]

ACE service to Santa Clara station began in 2001, was suspended in 2005, and returned in 2012.

The original service used two trainsets, each with four bilevel coach cars, for a total seated capacity of 1,120 passengers in each direction daily. In September 1999, less than a year after opening, the service reached 1,000 daily riders per direction, near full capacity.[11]

With that success, the agency wanted to add additional runs. To enable more trains on the line, ACE funded $3 million in track improvements,[12] but the limited amount of equipment only allowed ACE to add a morning "short turn" run between San Jose and Pleasanton. This "turn-back train" started service on February 21, 2000, and gave Pleasanton and Fremont a third inbound train to alleviate the crowding on the two earlier trains.[13] Even with the added capacity, by early 2001 ACE was regularly carrying more than 700 daily standees.[14]

ACE purchased additional equipment, allowing the "turn-back train" to operate to Lathrop/Manteca station, nearly the full length of the route, beginning on March 5, 2001; trains also began stopping at Santa Clara station.[15] Although the third train added 560 seats in each direction, it brought an immediate increase of 380 daily riders.

ACE then planned to add a fourth round trip later in the year, with fifth and sixth round trips by 2006.[14] 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.[11] 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.[16]

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.[8] Suffering from reducing funding due to the Great Recession, ACE cut the lightly used midday trip on November 2, 2009.[11] On May 14, 2012, ACE restored service to Santa Clara station.[7][17] On October 1, 2012, a fourth rush-hour round trip was added, running approximately one hour after existing trips.[11]

Car in new Altamont Corridor Express livery at Fremont station in July 2018

In December 2012, the service was rebranded from Altamont Commuter Express to Altamont Corridor Express to reflect plans for a broader scope of service.[18]

In March 2014, ACE opened a $65 million, 121,000-square-foot (11,200 m²) maintenance facility in Stockton.[19] On July 1, 2015, management and governance of the San Joaquin passed from Caltrans to the new San Joaquin Joint Powers Authority.[20] 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.[21][22]

ACE received Road Repair and Accountability Act funds in order to initiate Saturday service in January 2018,[23] with two Saturday round trips added in September 2019.

ACEforward
Natomas/Sacramento Airport Sacramento RT Old North Sacramento Midtown City College Elk Grove Sacramento RT Lodi Stockton North Lathrop (relocated) Lathrop/Manteca Manteca (potential) River Island Ripon Downtown Tracy Stanislaus River (option) West Tracy Modesto Tuolumne River (option) West Tracy Ceres Phase 1 Phase 2 West Tracy Turlock Merced River tunnel option Livingston Altamont Pass Atwater (potential) (potential) Greenville Road Merced ACE or DMU service to Isabel BART or Dublin/Pleasanton Niles Canyon Railway ACE or DMU service to Union City Fremont double tracking to Santa Clara Diagram shows all alternatives; not all will be implemented[24][25][26]

In association with the California High-Speed Rail project, the ACE line is 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.[27]

As the high-speed rail 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;[28] this was released in 2017 and prioritized goals as either long term or short term.[29] 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 and electrification of the line from Stockton to San Jose.[29]

Also under studied were possible connections with BART at Union City or the Tri-Valley[30][31] via traditional ACE rail, diesel multiple units, or bus bridges.[32] This connection is planned to be facilitated by the Tri-Valley-San Joaquin Valley Regional Rail Authority.[33]

The state senate allocated $400 million in revenue from a gas tax increase to ACEforward expansion.[29] ACE was awarded $500.5 million in April 2018 for expanded service to Ceres and Sacramento[34] to provide more rail service and connections within the Central Valley.[35][36] Service is expected to begin from Ceres by 2023[37] 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 North Lathrop.[38]

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.[39] The Union Pacific right of way between Ceres and Lathrop will be double tracked to facilitate passenger service.[37] As of 2019 platforms are being extended to accommodate longer trains.[40]

Valley Rail is the project to route ACE and Amtrak San Joaquins along the little-used Sacramento Subdivision between Stockton and Sacramento. Six new stations would be constructed along the line with a layover facility at Natomas. Trains would run the length of the line from Natomas to San Jose or Ceres with a midday short turn to Stockton. A Draft Environmental Impact Statement was released in 2020, with services expected to begin no later than 2023.[41] The North Elk Grove station was eliminated from planning in September 2020.[42] The project received funding via California's Transit and Intercity Rail Capital Program in 2023, by which time the project was expected to open in phases beginning in 2025.[43] Later that year, the estimated commencement of service to Ceres and Natomas were again pushed back to 2026, with service to Merced and infill stations opening by 2030.[44]

Altamont Corridor Express train crossing the San Francisco Bay National Wildlife Refuge between Fremont and San Jose

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 Lathrop, the line uses the Oakland Subdivision.[47][48] From Lathrop to Stockton, the line uses the Fresno Subdivision.

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.[49]

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.

ACE fares are distance-based and available in one-way, round trip, 20 trip, and monthly passes. Unlike many of the other commuter rail services on the West Coast, ACE does not have ticket machines at stations. Passengers are encouraged to use the railroad's mobile ticketing app, but paper tickets can be purchased from agents at all stations expect Vasco Road and the Santa Clara Transit Center. Also, unlike many other transit services in the Bay Area, ACE does not accept the Clipper Card.