CALIFORNIA is one of the states of America that is feeling the effects of climate change the most. Uncontrollable wildfires, increasing temperatures, crippling droughts and rising sea levels are already impacting the way of life in the Golden State, with a worsening outlook for the future.

As it often does, California is leading the way in the United States, in this case on attempting to tackle the climate crisis. The state government has committed to an ambitious decarbonisation strategy centred on sourcing more and more energy from alternative, greener sources. It is also encouraging greater energy efficiency among citizens and introducing clean technologies wherever possible.

Specific goals include reducing carbon emissions to 1990 levels by 2030. This equates to taking 5.6 million cars off the road every year and reducing annual emissions from 14 to 10 tonnes per person. In transport, the state requires by law that all new cars and lorries sold in the state are emission-free by 2035, with a recent tightening of the legislation ramping up requirements for the proportion of zero-emission vehicles sold from 2026 to meet the 2035 target.

The plan to decarbonise transport includes rail. As part of a wide-ranging package of measures, the California Air Resources Board (Carb) passed a ruling in April 2023 requiring that no locomotive aged 23 years or older will be permitted to operate in the state after 2030. In addition, all shunting and passenger locomotives built after 2030 and at work in California will have to operate in zero-emissions configuration. This is extended to 2035 for mainline freight locomotives.

The measures also include limiting idling to 30 minutes and introducing the In-Use Locomotive Regulation under which users pay a fee determined by the level of emissions generated by an individual locomotive while in California. The money collected will help pay for upgrades to cleaner locomotive technologies and Carb says the regulation is projected to contribute the largest overall reduction in nitrous oxide emissions before the 2037 deadline for improving California’s air standards.

Carb says together the measures will help to achieve $US 32bn in health-related savings. However, it is proving controversial with the rail freight industry. Last June the Association of American Railroads (AAR) and the American Shortline and Regional Railroad Association (ASLRRA) launched a lawsuit against Carb. They argue that despite investing millions on exploring alternative traction, the rail freight industry has yet to identify a clear technological path towards zero emissions and that the ruling is too restrictive. With just 1% of greenhouse gas emissions coming from locomotives nationally, they are perhaps correct to feel aggrieved.

The situation with mainline passenger rail is quite different. State-owned Caltrans has been considering zero-emission operation since the late 2010s, issuing its own California Inter-city Zero Emissions Strategy in 2020, following the receipt of grant funding to develop the study with German Rail’s (DB) US consultancy business DB ECO in 2018. The goal is for inter-city rail to take the lead among other modes of transport by operating an entirely 100% emission-free fleet by 2035. Yet the path to achieve this and what specific type or types of alternative traction to deploy is tricky.

Caltrans owns the rolling stock operating on three inter-city corridors where services are managed by regional Joint Powers Authorities and operated by Amtrak. As Mr Kyle Gradinger, division chief of rail and mass transportation at California Department of Transportation (Caltrans), reveals, the study provided an in-depth evaluation of all the potential propulsion solutions that might be used on these corridors - diesel and renewable diesel, natural gas, batteries, hydrogen and electric.

“We considered everything from initial cost and operating expenses to energy consumption, fuel availability and the infrastructure changes required,” Gradinger says.

The results were intriguing, with hydrogen emerging as the standout candidate for Caltrans’ use cases.

“Some of the key factors in that analysis that put hydrogen over battery and electrification for us were related to cost-effectiveness,” Gradinger says. “They can be slightly more expensive than diesel trains but in the long term they would offer operational cost savings. They also require minimal changes to the existing infrastructure.”

Indeed, what Gradinger describes as the “gold standard,” electrification, is deemed impractical due to the sheer cost involved and because virtually all of the infrastructure on which California’s inter-city passenger trains run is owned by Class 1 freight railways, predominately Union Pacific (UP).

“We will go out and advocate for electrification all day long,” Gradinger says. “But it’s their property, it’s their economics, it’s their business decision, it’s their choice. And while we can advocate for it, we’re not going to go there and tell them they must do this, we’re not in that position.”

Likewise, battery power was considered prohibitively expensive, in particular the development of a charging network. A fixed hydrogen refuelling station is estimated to cost $US 50m, a fraction of the equivalent solution for charging batteries, and this the major driver of hydrogen’s expected operational cost savings. In addition, the range of battery trains is significantly less than for hydrogen-powered vehicles.

“The combination of their extended service range and rapid refuelling capability meant that hydrogen trains were really aligned well with the operational dynamics of the inter-city service that we do today,” Gradinger says. “We didn’t want to have to go out and buy additional trains, maybe twice as many battery-electric trains, because you would have them sitting out for five, six hours at a time to charge. You would basically have a one for one replacement.”

The extended range is essential to meet the demands of Valley Rail. The San Joaquin Regional Rail Commission is currently overseeing a project to improve the quality and frequency of mainline passenger services between the Central Valley, Bay Area and Sacramento regions. This includes extending the Altamont Commuter Express to Sacramento and Ceres and expanding services on the San Joaquin Line between Sacramento, Merced and Fresno, including adding the new hydrogen inter-city service from Sacramento to Stockton and Merced, where it will offer cross-platform interchange with trains operating on the future 275km Bakersfield - Merced high-speed line, the first section of which is expected to open in 2029-30.

Introduction of the Valley Rail hydrogen service requires infrastructure upgrades, including track doubling of much of the existing UP-owned line on which the hydrogen trains will run. There will also be improvements to signalling and several level crossings will be eliminated. The key project is the $US 237m Stockton Diamond Grade Separation, a BNSF-UP interchange, which is described as the busiest and most congested rail bottleneck in California. The scheme involves elevating the north-south UP track to pass over the east-west BNSF track on a new structure that will be built just to the east of the existing lines. Construction is expected to begin this month.

The infrastructure improvements are expected to be completed to Modesto, north of Merced, by 2027, in time for the start of line testing of the first two of the new fleet of 10 Flirt H2 hydrogen four-car multiple-units ordered by Caltrans from Stadler, which are due to arrive that year. The full improvements to Merced are then expected to be completed by 2029, when the remaining eight trains will be delivered. “The hope is that high-speed rail will have their initial segment up to Merced by around 2029,” Gradinger says.

Caltrans and the California State Transportation Agency (CalSta) placed an initial $US 80m order with Stadler for four hydrogen trains in October 2023. This was followed by the exercise of an option for another six trains in February, taking the total contract value to $US 207m. Options remain to purchase another 19 trains.

These will not be California’s first hydrogen trains, however. The San Bernardino County Transportation Authority (SBCTA) ordered a single four-car hydrogen train to operate alongside the two Flirt DMUs now running on SBTCA’s 14.5km Arrow Line between San Bernardino Transit Center and the University of Redlands. The train was one of the star exhibits at InnoTrans in 2022, and after undergoing testing in Switzerland, it was shipped to the United States in 2023. It has since undergone extensive testing at the Transportation Technology Center in Pueblo, Colorado. This includes achieving a Guinness World Record for the longest single operating distance recorded by a hydrogen fuel cell multiple-unit without refuelling - 2203km.

Operation of the Arrow Line hydrogen service is expected to begin later this year. Caltrans funded procurement of the SBCTA Flirt fleet and Gradinger says the agency has stayed in close contact as the project has progressed. He says SBCTA’s work has proven invaluable in figuring out, often by trial and error, what is the best way to introduce a zero-emission hydrogen train into service. This includes the key work to design maintenance and stabling facilities for the new trains well in advance, as well as identifying a refuelling strategy.

“SBCTA has been a forerunner in working with fire departments and local safety organisations on designing a facility to meet international codes for hydrogen and also working with local fire departments to train them on what to do with fire safety,” Gradinger says.

Likewise, he says Stadler and SBTCA have been open in sharing intensive testing information throughout the trials at Pueblo, including any design improvements that have been made, helping to deepen Caltrans’ understanding of the train and the new technology. This includes the introduction of a haptic feedback buzzer to inform the driver when they have achieved optimal acceleration, or braking so they can maximise the energy recovered through regenerative braking. “This process has been really helpful in giving us confidence that we’ve got the right partner,” Gradinger says.

The North County Transit District has expressed an interest in trialling hydrogen on its 66km Coaster service from Oceanside to San Diego.

Trials are expected to begin on the Arrow Line this month. The hydrogen train itself is based on the Flirt platform that is widely tried and tested in the United States. Gradinger points out that the only real modification that has been made compared with the diesel-battery version is the use of a hydrogen fuel cell instead of the diesel engine and generator.

“There are things we have learned from the SBTCA vehicle about hoses and fittings and pressures and things like that, but otherwise we don’t have to worry about the design concept,” Gradinger says. He adds that the Flirt has already secured Tier 1 crashworthiness and Tier 1 alternative crashworthiness certification from the Federal Railroad Administration (FRA), helping Caltrain to avoid going through this process with another hydrogen train, such as the Alstom Coradia iLint or Siemens Mireo Plus H.

“We are working really closely with the FRA safety and research and development offices so that we can make sure that we are checking all the boxes and addressing any concerns that they may have about the hydrogen, about the propulsion, so we don’t get any nasty surprises at the end,” Gradinger says.

Caltrans is also actively engaged in a process to identify partners to source the required hydrogen fuel and to develop the related infrastructure. This is the major challenge to delivering the inter-city rail hydrogen project. Gradinger says partners within the state government, at non-profit organisations and academic institutions are helping in this infrastructure development process. More generally, California is gearing up to develop hydrogen fuelling infrastructure as part of its wider decarbonisation strategy, with Caltrans very much riding on the coat tails.

Among key initiatives in California is the establishment of one of at least four nationwide hydrogen hubs in the state. The Biden administration’s Hydrogen Earth Shot Challenge is aiming to reduce the overall cost of clean hydrogen from around $US 5 per kg to less than $US 1 per kg within a decade. The US Department of Energy is allocating $US 1.2bn to the government of California to support hydrogen projects at the Arches H2 Hub, a public-private partnership (PPP) that will bring together clean hydrogen producers, consumers and infrastructure to deliver technology demonstrators and deployments, including for transport infrastructure.

In addition, California’s Department of General Services, which is responsible for major state procurement projects, has issued a Request for Information (RFI) to the fuel industry to assess the appetite for producing large quantities of hydrogen and to supply green hydrogen as quickly as possible. Gradinger reports that the response to the RFI has been positive. A statement from the Department of General Services confirms that the feedback offers confidence “that the industry is well prepared and interested to respond if a future Request for Proposals comes out for statewide hydrogen procurement.”

“It takes a village, it’s not just us buying the train, it is going to be an ecosystem,” Gradinger says. “We’ve got partners working across all aspects of the industry from production to distribution. And I think with a critical mass and the buying power of the State of California, we’re in a strong position.”

The 2027 delivery of the first train appears to be focusing minds on sourcing the required fuel. Gradinger expects that the 10 Flirts will require 3000kg of liquefied hydrogen per day, or 1100 tonnes per year. The colour of this hydrogen is unlikely to be “green” from the start, however. But with procurement tied to Carb requirements for low-carbon fuels, Gradinger also does not expect to receive what is deemed “grey” hydrogen either, but something that is very much on the path to being green.

This is apparent in the state’s steady shift away from fossil fuels for energy generation. California already benefits from an abundance of solar and wind energy - it accounted for a record 103% of the state’s energy demand on a windy Saturday morning on May 8. Capacity is only going to increase as the state strives to move away from fossil fuels completely. “There’s a lot of potential to use the energy that is being created to create hydrogen and store it,” Gradinger says.

Gradinger says a study is nearing completion of the work required to modify the San Joaquin Joint Power Authority’s (SJJPA) maintenance facility to maintain the hydrogen fleet. Studies of a potential conversion to a fixed hydrogen refuelling station are planned but have not yet begun, so SJJPA will initially deploy a mobile refuelling concept for the Flirt H2. This will help to reduce initial costs and maximise operational flexibility for the Valley Line service. It also offers the opportunity to trial hydrogen operation on other lines in the state.

Gradinger reports that the North County Transit District (NCTD), which oversees the Coaster commuter service in San Diego, is interested in seeing how hydrogen performs on the coastal route. He adds that he would like to see how the Flirt H2 will perform on steeper gradients. Discussions have been held with Metrolink about trials on the 123km Antelope Valley Line between Lancaster in northern Los Angeles and LA Union Station.

“All it takes is for a mobile fuelling truck to go down there and test that for six months,” Gradinger says. “This isn’t going to be the solution for every corridor in California, but we do want to see where else it can work.”

He is also optimistic that the hydrogen fuel cell will have the capability to power a six-car Flirt train in the future. However, with some services in the state such as the Pacific Surfliner operating with six or seven double-deck coaches, hydrogen is unlikely to be the solution everywhere.

Certainly, with 37 US EPA Tier 4 compliant SC-44 Charger locomotives built by Siemens introduced in California over the last few years and expected to continue operating into the 2040s, diesel is not going away just yet. Gradinger also does not rule out battery operation in some circumstances, particularly where electrification is taking place, notably on the 82km line operated by Caltrain between San Francisco and San Jose, another project that Caltrans has funded (see panel p34). “We want to see if we can do a battery-electric version of the Kiss [EMU], take that off wire all the way down to Gilroy and potentially even Salinas, a little further down the line,” he says.

The future fully electrified high-speed line between Burbank and Los Angeles and Fullerton could also offer similar opportunities for dual-mode trains to operate if it is not possible to extend the electrification.

With California investing in the infrastructure necessary to produce hydrogen fuel at scale, and universal electrification all but impossible to obtain in the current climate, hydrogen rail operation is certainly viable, as the state’s zero emissions study revealed. It is by no means a solution for everywhere, and doubts over its capabilities are often justified. But with legally-binding regulations driving a change in how rolling stock will be powered in the next 10-15 years in California, hydrogen is very much the fuel of the future here. It is also likely to gain traction as a solution in many other regions as they grapple to comply with strict climate change-related legislation.

Caltrain is set to introduce electric passenger services between San Francisco and San Jose this autumn.