The right route to US rail decarbonization is electrification

The Effective Transit Alliance is a group of railroad experts, planners, and mathematicians whose academic focus is the cost efficiency and operational efficiency of transit agencies worldwide, although they have a particular focus on the New York region.

The most recent publication is a direct response to the US Department of Energy's RFI (Request for Information) about zero-emission rail propulsion technologies. They address the questions of what technologies are currently the most feasible and will be the most feasible in future decades, existing efforts to decarbonize, and benefits and challenges of various solutions.

Their argument is that railroad electrification is an essential step toward decarbonization. They strongly prefer electrification from overhead electrical systems (catenary wires) over diesel for carbon and efficiency/maintenance reasons; and over batteries or hydrogen for weight/energy density reasons. In short, while overhead wiring has a relatively high upfront cost, it is the most viable solution with the greatest benefits.

Other (much poorer) countries have successfully electrified significant portions of very large railroad systems, both for passengers and freight. Overhead electrification technology is proven. There are no serious technical barriers here, only perceived ones. Some lines do benefit more than others, but the US has a lot of lines that qualify, including virtually every regional rail system of every major metropolitan area, most of which are not electrified. Many inter-city lines would also be suited to electrification, given their very high traffic from passengers and/or freight.

A recent study of passenger rail electrification by the Verband der Elektrotechnik, Elektronik und Informationstechnik (VDE), a German technical association that maintains electrical safety standards, found that—while the breakeven point depends on the size of the train, the terrain, and the difficulty of wiring—a line is typically best served by overhead wire if it runs at least two-car regional trains every half hour or more at the peak and best served by battery technology below that service level [8]. It found hydrogen to be completely cost-ineffective.

High-speed rail routes require electrification of some sort. It is essentially physically impossible to get a diesel train to run at 300 km/h (186 mph) and even more impossible for it to be economical. High-speed passenger trains also need to be fairly light, unlike slower freight trains, so heavy batteries or other heavy/space-inefficient fuels are not suitable. Offloading energy storage into an overhead wire allows the trains to be much lighter and faster.

Benefits of electrification generally, emphasis mine:

Rail systems benefit from OLE electrification for several reasons:

• Reliability: Electrified systems benefit from at least a tenfold increase in reliability over diesel trains [9]. Perhaps counterintuitively, electric trains are so much simpler to operate and maintain than the diesel trains that dominate US railroads that their cost savings more than offset the maintenance cost of the wire they use to operate. Electric trains contain far fewer moving parts than diesel ones. In most cases, the electric motors—one per axle—are the only moving parts. In contrast, diesel trains rely on an internal combustion engine with pistons and a crankshaft to turn a generator that powers the same electric motors attached to the wheels, a far more complicated arrangement with much greater wear due to vibration from the engine.

• Acceleration: At typical suburban rail speeds, modern self-propelled electric trains —called electric multiple units (EMUs)—save around 30 seconds of travel time per stop over diesel train sets of the same passenger capacity. This not only speeds service but also permits planners to add more stops to schedules with minimal impact on overall travel time, increasing the usefulness and legibility of service. In the Bay Area, for example, Caltrain plans to turn many limited-stop trips into local trips when it converts to EMUs; local trains from San Francisco to San Jose will be 25% faster than today [10].

• Power-to-weight ratio: Electric trains that draw power from an overhead or trackside power supply are much lighter, and can draw more power, than those that carry a diesel engine, hydrogen fuel cells, or batteries. This is one reason electric trains accelerate faster. Moreover, as they can draw surge power for short times, electric trains can climb steeper grades than diesels can manage. It is telling that mountainous Switzerland has a fully electrified system, and that the longest continuous section of electrified track installed in the United States was the Milwaukee Road’s Pacific Extension, which crossed the Rockies and Cascades.

• Lack of pollution: Electric locomotives do not emit combustion pollutants, so nearby communities benefit from cleaner air. The same is true of travel through tunnels, which by their nature limit ventilation. Right now, the performance of diesel trains through such key tunnels as the Stevens Pass is limited by the exhaust capacity of ventilation systems, creating choke points on important transcontinental routes. In an urban context, many commuter lines that pass through dense neighborhoods with high asthma levels still run polluting diesel locomotives, for example Boston’s Fairmount Line [11].

• Higher ridership: All of the benefits mentioned above don’t merely reduce long-term operating costs and environmental impact, they also provide a better experience for passengers. The result is increased ridership, a phenomenon that British proponents of rail electrification call the sparks effect [12].

All of these benefits scale with rail traffic. For example, consider passenger systems that run a large amount of peak service. This requires a large number of train sets. Not only do EMUs cost less to operate, but because they are faster and more reliable, fewer train sets are required to run a given service level. As a result, electrification brings major lifecycle cost savings. The same phenomenon applies to air pollution. Since pollution is created by each and every moving train, electrifying busy main lines can massively reduce pollution. This means that the returns on electrification are the highest on the most intensively-used lines. This is why typically electrification programs begin with commuter lines, as they did in early-20th century America with New York- and Philadelphia-area lines.

Nonetheless, the American rail network has so little electrification and so much rail traffic that there is a strong case for electrifying substantial parts or even the entire national network of passenger and Class I freight rail lines.

The ETA also specifically call out the misconception that electrification is infeasible on freight routes:

As early as 2010, a majority of Indian rail freight traveled on electric trains [16], at which point 30% of its network was electrified. Since then, it has completed OLE over nearly the entire country’s network. While some US freight railroads claim that it is not possible to operate double-stacked freight under OLE, both China and India already run extensive double-stacked electric freight under wires. In the US, CSX runs double-stack freight powered by diesel locomotives underneath traction wire on the SEPTA West Trenton Line [17].

Clearly, it's already being done, and it's already being done well in some places. The US simply chooses not to make the investment. They have some discussion about costs and conclude that the costs are not too high; electrification projects would be large, at around $2 million/mile, but far from unusual. This figure is in line with other transit project costs that the federal government has agreed to fund with no reservations. It is also in line with typical per-mile highway costs.

Batteries are suitable only as a supplement to overhead catenary electrification:

While battery freight locomotive technology has made some strides, the most powerful units can still only supplement diesel propulsion over relatively short distances [23]. Current battery energy density reaches less than 10% that of diesel fuel. That is expected to increase to 15% diesel’s energy density by 2035, which would still imply bulky and heavy onboard energy storage [24]. Battery vehicle range suffers in cold weather [25]. Due to that drawback, battery freight locomotives are likely to find their greatest use in first- and last-mile solutions such as yard and facility switching, and line-haul application almost certainly favors traditional OLE.

First, BEMUs have around a 100% cost premium over conventional EMUs [31]. [...] Moreover, charging time drastically lengthens the amount of time that trains lay idle, requiring more trains to be purchased for a given service level than with OLE.

Second, most BEMU projects save little infrastructure capital cost over traditional OLE. To avoid significant charging time as mentioned above, BEMUs nearly invariably require extensive wired track to charge en route. Worse, the substations must supply high power intermittently to charge the batteries, increasing their cost and negative impact on the grid.

Third, battery trains are likely to be slower and less reliable than their EMU counterparts, reducing ticket revenue and mode share. The combination of weather and limited battery service life is likely to introduce significant variability in charging times at endpoints. [...] On that train set, the power reduction [of 25% due to the batteries] adds 15 to 20 seconds of runtime per stop.

Hydrogen-powered trains are incredibly energy-inefficient relative to overhead catenary electrification:

Hydrogen-powered trains, another occasionally proposed alternative to OLE, fare worse against it than battery stock, and an overall energy efficiency of less than 40% (compared to about 90% of conventional OLE electric trains) [34]. Baden-Württemberg found hydrogen solutions would cost nearly double either battery trains or a fully wired system [35]. An analysis by Deutsche Bahn found that per seat-mile, hydrogen or battery propulsion would consume double the energy of overhead electrification [36]. Moreover, the water required to produce hydrogen for propulsion is likely to strain supply in dry areas [37].

Further reading:

• Overhead Electrification for Railways by Garry Keenor
• National Electrical Manufacturers Association Rail Electrification Coalition response to DOE RFI
• Official Rail Passenger Association of California and Nevada (RailPAC) response to DOE RFI