[a] From January 2015 to December 2023, a total of $11.2 billion had been spent on the IOS – which has 119 miles (192 km) under active construction – and on upgrades to existing rail lines in the San Francisco Bay Area and Greater Los Angeles, where Phase 1 is planned to share tracks with conventional passenger trains.

However, the Authority has not yet received sufficient funding to construct the segments from the IOS westwards to the Bay Area or southwards to Los Angeles, both of which would require tunneling through major mountain passes.

[14] Proposition 1A, which passed with about 53 percent of the vote, set several requirements for the high-speed rail system, including that the nonstop travel time from the Salesforce Transit Center in San Francisco to Los Angeles Union Station should be no more than 2 hours and 40 minutes.

[25] The existing 4th and King Caltrain station in San Francisco is expected to be the northern terminus of Phase 1 until the future completion of the Downtown Rail Extension (now known as The Portal) to the Salesforce Transit Center.

[27] As part of Phase 1, Merced is planned to serve as a transfer point to the Amtrak San Joaquins and Altamont Corridor Express (ACE)[b] trains continuing towards Stockton, Sacramento and other destinations.

[57] Engineering challenges along this section include "poor-quality rock formations, faults and shear zones, and potentially high groundwater inflows that can affect tunnel stability.

[59] At a press conference in January 2025 in Kern County, state and CHSRA leaders reiterated the importance of this section and promoted the vision of a combined CAHSR-High Desert Corridor-Brightline West rail corridor.

[86] Brightline West (formerly Desert Xpress and XpressWest) is a project that has been planning to build a high-speed rail line from Las Vegas, Nevada to Victorville, California – about 90 miles (140 km) northeast of Los Angeles – since 2007.

To bring the IOS into revenue service (including trainsets, stations, and maintenance facilities) along with ongoing project development for Phase 1 and statewide connectivity programs (blended corridor investments, such as the Caltrain electrification), it estimates nominal expenditures ranging between $28.5 and $35.3 billion, adjusted for schedule.

[113] In September 2023, the Authority obtained a $202 million FRA grant to design and construct six grade separations in Shafter, California,[114] part of the southward extension from the initial 119 miles (192 km) towards Bakersfield.

The same grant also approved $3 billion for Brightline West, a similar but privately-run high speed rail project aiming to connect Los Angeles with Las Vegas.

As of December 2023, full completion of the IOS along with the ongoing investments into blended corridors for Phase 1 and program-wide costs (such as administration, project development, trainsets, and maintenance facilities) is expected to entail a funding shortfall of between $200 million and $7 billion.

[121][122] Unlike the estimates at project inception, this cost revision considered necessary construction of viaducts to cross multiple freight railroads (owned by BNSF and UPRR), floodplains, and irrigation canals.

He anticipated that potential change orders for the CAHSR project in case of land conveyance issues could cause construction delays and cost increases, but that "[t]hese aren’t huge.

This resulted in a requirement for the Authority to construct costly intrusion protection barriers – thick walls made out of steel reinforced concrete – to separate its guideway from freight lines.

According to the Authority, a final agreement with the FRA and the affected freight rail companies BNSF and Union Pacific on technical specifications for such barriers was reached only in December 2016,[153] well after construction contracts had been issued.

"[163] In 2017, the California Supreme Court ruled in another case that federal regulations of the Surface Transportation Board do not categorically preempt projects such as CAHSR from compliance with stricter state environmental laws.

However, the estimated ranges below do not factor in cost revisions that are expected to occur upon environmental clearance for two sections in Southern California (Palmdale to Burbank, and Los Angeles to Anaheim),[x] planned for the end of 2025.

Jerry Brown stated in 2012: "During the 1930's, the Central Valley Water Project was called a ‘fantastic dream’ that ‘will not work.’ The Master Plan for the Interstate Highway System in 1939 was derided as ‘New Deal jitterbug economics...

Congressman Kevin McCarthy (R-Big Bear Lake), a native of Bakersfield, stated that he would "do whatever I can to ensure that not one dollar of federal funds is directed to this project",[108] a few days before becoming House majority leader.

"[184] In 2015, the Train Riders Association of California described the high-speed rail project as "throwing good money after bad" and argued that upgrading the existing Pacific Surfliner and San Joaquins services would provide more benefits per dollar.

[185] While the environmentalist organization Sierra Club initially supported the project, they shifted to opposing it in 2014, arguing that California should prioritize spending on other efforts to fight climate change, as high-speed rail's benefits would take decades to realize.

[199] However, the Lowy Institute notes that the Indonesian corridor is short (less than half of the California IOS[199]) and already served by frequent rail service while its tickets are twice as expensive, limiting the line's attractiveness to passengers.

[200] The Los Angeles Times wrote: "fares will be one of the most important factors in the decisions that millions of travelers will make when choosing to fly, drive or ride the bullet train.

A 2015 report prepared by Eric Eidlin of the U.S Department of Transportation noted that while these were downsides of blended operation (as is the case for high-speed rail in Germany), there were also potential benefits, such as improved transit connectivity from sharing existing stations, and reduced noise and environmental impacts.

Critics such as the California Rail Foundation[223] and Samer Madanat, director of the Institute of Transportation Studies at UC Berkeley,[224] have noted that Altamont would provide a more direct link from the Stockton and Modesto areas to San Francisco, compared to Pacheco which requires a long detour to the south.

[223][225] As of 2020, the Sierra Club also opposed the Pacheco route in favor of Altamont, citing the greater impacts of the former on Coast Range wildlife and its potential to induce urban sprawl in the countryside surrounding Gilroy.

[226] Sprawl has been a general concern since the early planning of the project; a station in Los Banos – which the Pacheco route passes between Gilroy and Merced – was specifically prohibited by Prop 1A as a compromise for the Sierra Club and other environmental groups to endorse the ballot.

[228] Planned upgrades to other existing Northern California rail lines are expected to improve service and increase speeds through Altamont Pass, as well as from Sacramento to the Bay Area.

"[239][240] The project has impacted agriculture along its route in the Central Valley, with portions of several large properties being cut off from access, disruption of irrigation systems, and a reduction in the acreage available for farming.