Hybrid Locomotives, Vehicle Electrification at Relevant Scale

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John Petersen

Last month Ricardo PLC (RCDOF.PK) published a report titled “GB Rail Diesel Powertrain Efficiency Improvements” that it prepared for Great Britain’s Department for Transport. While most of the fuel efficiency technologies Ricardo evaluated for the report were mechanical systems, its analysis of the fuel efficiency benefits of stop-start and hybrid systems for locomotives offered an intriguing view of a cost-effective vehicle electrification opportunity that can be implemented at relevant scale within a few years. The two types of locomotive systems Ricardo evaluated for the report were simple stop-start idle elimination and full hybridization. The following table compares the relative fuel economy benefits of these alternatives for local, intercity and freight trains in Great Britain.

Technology level Local Intercity Freight
Stop-start idle elimination up to 7% up to 4% up to 41%
Hybrid powertrain up to 22% up to 14% up to 41%

While raw percentages are fascinating, they can’t give you a feel for the magnitude of the potential fuel savings. On its website, the Electro-Motive Diesel unit of Caterpillar (CAT) helps put the Ricardo numbers into perspective by showing how a basic stop-start system can offer 10-year savings of up to $357,308 for a switcher duty cycle and up to $222,740 for a line-haul duty cycle. With full hybridization, the fuel savings can be even more striking.

For the last couple years General Electric (GE) has been preparing to launch its Evolution™ Hybrid Locomotive, which will save approximately 440,000 gallons of fuel over a 20-year useful life, or roughly $1.3 million based on an assumed diesel price of $3 per gallon. In February, Japan Freight Railway Company introduced a hybrid shunting locomotive that slashes fuel consumption by 36%. Both of these hybrids are diesel-electric locomotives that were redesigned to capture the energy dissipated during braking and store it batteries. The stored energy can then be used on demand to reduce fuel consumption. The Evolution hybrid uses a GE variant of the Zebra sodium nickel chloride battery that was originally developed by Daimler and refined by FZ Sonick. JR Freight’s hybrid shunting locomotive uses a surprisingly small (67.4 kWh) lithium-ion battery pack from Japan’s GS Yuasa (GYUAF.PK).

Between now and 2020, Pike Research forecasts that cumulative sales of new hybrid locomotives will approach 500 units worldwide and require roughly 500 MWh of batteries. While Pike expects new hybrid locomotive sales to ramp rapidly through the end of the decade, the larger near-term opportunity will involve retrofitting the existing global fleet of about 100,000 diesel-electric locomotives to save fuel, reduce emissions and improve the bottom line performance of the world’s cheapest land-based transportation networks.

Most developers of hybrid locomotive technologies have followed the path blazed by automakers and tried to build all necessary elements of a hybrid system into a single chassis. The exception to the general rule has been Norfolk Southern (NSC), which is focused on developing a pure battery electric locomotive that can be:

  • Charged from the grid and used as a stand-alone locomotive for yard switching operations; or
  • Combined with one or more conventional diesel-electric locomotives to create a “hybrid train.”

Norfolk Southern’s battery electric locomotive technology is described in US Patent No. 8,136,454, which issued on March 20th of this year. The beauty of the patent is its inherent simplicity and flexibility. Designing a single-chassis hybrid locomotive is a very complex engineering and space optimization challenge. When the battery elements of the system are separated from the internal combustion elements, however, the engineering and space optimization hurdles get lower while overall flexibility increases.

There are very few industries that can compare with the railroads when it comes to calculating the amount of fuel needed to move a train over a given route. The route data is all computerized with precise grade and speed profiles for every foot of track. If a route needs a five to one balance between diesel and battery power, a railroad can configure a six locomotive consist with five diesel electrics and one battery electric. If another route can handle a one to one balance, a railroad can configure a six locomotive consist with three diesel electrics and three battery electrics. That ability to mix and match locomotives to suit the precise requirements of a particular route simply can’t happen with single-chassis hybrids.

The concept even makes the retrofit process cheaper since a railroad can convert its least efficient locomotives to battery drive, keep its most efficient locomotives as diesel-electrics, and effectively upgrade the entire fleet by retrofitting a small percentage of the rolling stock.

Norfolk Southern’s first battery-electric locomotive, the NS 999, was publicly launched in September 2009 but severe charge acceptance problems in the AGM batteries it used for the original vehicle had Norfolk Southern actively searching for better batteries by the time the November-December issue of its employee magazine,“BizNS,” was published. Since 2010, the primary focus of Norfolk Southern’s battery evaluations has been the PbC battery from Axion Power International (AXPW.OB), an asymmetric lead-carbon battery that offers the cycle-life, charge acceptance and power of lithium-ion batteries at a lead-acid price point. While the two companies have been tight-lipped about their progress, Axion has reported that the PbC is meeting all expectations in double redundant long-string testing at Axion, Norfolk Southern and Penn State University. In a presentation at last October’s William W. Hay Railroad Engineering Seminar hosted by the University of Illinois at Champaign-Urbana, Gerhard A. Thelen, Norfolk Southern’s Vice President of Operations Planning & Support, spoke highly of the PbC’s performance and offered an upbeat outlook for Norfolk Southern’s battery-electric locomotive plans. Prototype trials of switching and long-haul battery-electric locomotives are anticipated later this year.

Stop-start idle elimination and hybridization of railroad locomotives and other heavy freight vehicles will never have the sex appeal of a Fisker Karma, but for companies like Norfolk Southern that spend $1.5 billion a year on fuel, knocking ten or fifteen points off the fuel bill with stop-start and hybrid locomotives is a compelling strategy.

Disclosure. Author is a former director of Axion Power International (AXPW.OB) and holds a substantial long interest in its common stock.


  1. Lots of into about fuel savings, but none about cost. Since you’re all about cost-effectiveness of fuel savings technology, I’m a bit surprised. Perhaps prices are hard to find, but you should be able to make some estimates based on the kWh (MHh?) of batteries used.

  2. Prices are hard to find and the railroads are being pretty tight-lipped, but it looks like the incremental cost is not nearly as significant as space constraints.
    Locomotives are odd beasts because they already have the electro-mechanical systems needed for a hybrid and the only thing they lack is batteries. some control systems and the space to put them.
    The technical equivalent of recuperative braking has been used on locomotives for decades. Unfortunately, the recovered energy is dumped into resistors where it’s blown off as waste heat.
    One of the fascinating factoids in the Ricardo report was that “the kinetic energy of a 50 ton rail vehicle traveling at 85 mph is 10 kWh. Modern freight trains travel slower, but frequently weigh 3,000 to 8,000 tons.
    The battery component of the NS 999 retrofit should come in at well under $1 million for a BMS and 1,080 PbC batteries. That makes the cost-benefit analysis pretty compelling.


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