These include a rerouted line through Tracy, an extension to Modesto and Merced, and connections to BART at Union City and Tri-Valley.

In November 1990, San Joaquin County voters passed Measure K, a half-cent sales tax to fund a variety of transportation improvements.

[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.

[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] 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.

[14] However, by late 2001, the deepening dot-com recession was severely hurting ridership, and expansion plans were put on hold.

At that time, service to Santa Clara was suspended to allow for the construction of a second platform and pedestrian tunnel at the station.

In association with the California High-Speed Rail project, ACE has developed plans to upgrade and expand service.

[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.

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.

[33] The California state senate allocated $400 million in revenue from a gas tax increase to ACEforward expansion.

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.

[34] However, during the development of ACEforward, significant financial and logistical challenges to expanding service on the existing route between Stockton and San Jose were identified, and further work on the project was halted in favor of a new Valley Rail project, focusing initially on the eastern expansion to serve commuters living in the Central Valley.

Trains would run the length of the line from Natomas to San Jose or Ceres with a midday short turn to Stockton.

[45] As of July 2019[update], ACE operated 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.

From Santa Clara to Stockton – the majority of the route – ACE runs on Union Pacific Railroad freight lines.

[51] 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.

The entire fleet of Bombardier bilevel coach cars and MPI F40PH-3C locomotives will be rebuilt, overhauled, and repainted to have a matching paint.