Five years after World War II ended, it became apparent to the railroads that steam locomotives were not the motive power of the choice. While a half dozen locomotive builders were assembling diesel-electric locomotives, the Electro-Motive Division of General Motors, with a head start in the 1930s and its U.S. Navy engine development during the war, took the lead. By the 1950s, EMD had settled into three locomotives product line categories: switcher, road switcher and road units.
While practically gone from the Class I carriers today, the look of EMD low-horsepower switcher locomotives with their high visibility cab and low engine hoods remains well known to railroaders. In modern times these were the SW1500 and MP15 models. EMD’s road switcher product consisted of a series of General Purpose (GP) models that included the GP7, GP9, GP18, GP20, GP30, GP35 and GP40 models over a two-decade period. While the latter models of this series were clearly road locomotives, the original intent of the GP models was to fulfill the role of “road switcher” units. This was a locomotive that could be used in local service, delivering freight and switching cars at a manufacturing plant, siding or yard. As diesel engine development progressed, later GP locomotives with their higher horsepower like the GP40, GP50 and GP60 were true road locomotives built for intermodal and high-speed merchandise trains.
In the early days, the “Special Duty” locomotives were a motive power product where high tractive effort at slow speeds was deemed desirable. Again, as engine development moved horsepower ratings from 1,500 to 3,000, niche models like the SD7, SD9 and SD18, evolved into to the all-purpose 3,000-hp road locomotive as 26 Class I carriers bought thousands of the SD40 (1,268 units) and SD40-2 (4,295 units).
After the 2024 election of POTUS 47 and the ensuing world events, the likelihood of increased regulations on locomotive emissions seems unlikely, at least for the short term. Yet concerns about the carbon footprint and particulate matter of diesel engines are not likely to disappear. While the production of Tier 4 locomotives is slowly picking up, the industry ponders what direction low- or zero-emissions locomotives may take.
Looking forward, the solution to lower emissions is likely to take on the characteristics of EMD’s three locomotive groups: switcher locomotives, units for local service and road locomotives for through freight trains.
Of these three categories, the solution for switchers is the most obvious. For switchers, the Battery Electric Locomotive (BEL) is the leading candidate. This “zero emissions” solution solves the problems where yards are in major metropolitan areas. Refueling occurs much like charging of highway Electric Vehicles, requiring 4-8 hours plugged into charging stations that require substantial capital investment. With battery technology progressing, battery charging times should continue to decrease while the total battery charge (stored kilowatts of energy) of BELs increases. While expensive at this time, BELs promise to solve the switcher locomotive emissions problem, starting with switch engines used in non-attainment areas, mostly in big cities.
The second category, the “road switcher” locomotive for local service, is likely a battery hybrid solution where batteries store energy and an onboard Internal Combustion Engine (ICE) provides battery charging on the fly. Based on the application, batteries and on-board charging can be sized and matched appropriately to optimize emissions and fuel reductions. Unfortunately, trends in rail traffic indicate a dwindling need for local service, the silver lining being only modest numbers of these locomotives will be required. For the foreseeable future, BELs will not be capable of fulfilling the speed and range requirements of local service, so hybrid solutions of sufficient horsepower are necessary.
The solution for road locomotives is less obvious. CPKC continues to face the Canadian carbon tax and thus advances its hydrogen fuel cell (HFC) solutions, successfully soliciting the interest of other large railroads. While CPKC works the bugs out of this technology, the refueling challenge remains large. Let’s start with the not-often-enough-stated fact that hydrogen remains highly flammable. Adding to the problems, the H2 hydrogen molecule is extremely small with a tendency to leak out of most everything. But the biggest problem of all is the distribution of hydrogen. Due to “hydrogen embrittlement,” pipelines are not viable for distribution. Keep in mind, while the Biden Administration actively promoted “Hydrogen Hubs,” they were just that, centers for hydrogen production and consumption. There was no provision for distribution. As valuable as CPKC’s work on HFC locomotive development is, work on hydrogen distribution is minimal.
An intermediate hydrogen fuel solution would be to use it in ICE locomotives first. Both Tier 4 engine solutions, Wabtec’s Evolution Series and the Progress Rail/Electro-Motive Diesel 1010J, could be adapted to hydrogen fuel. But only Wabtec is pursuing this, from what we know. Hydrogen fueled locomotives, of both types, require tenders. The good news is hydrogen tender development (provided by HGmotive) is maturing rapidly and in use at CPKC.
Even with the continued progress on battery technology, BELs won’t solve the road locomotive emissions challenge. Selective use of BELs to complement other locomotives in a consist, as demonstrated by Wabtec and BNSF, are promising. “Slugs,” locomotives with no source of electrical power that share power through large cables with adjacent locomotives, could serve a similar purpose and capture the lost energy of dynamic braking with regenerative braking. These concepts will make their way to commercial products so long as locomotive builders see commercial promise in such products.
Railroad operational managers love the fungible asset locomotive—a unit that can go anywhere and do anything. The SD70ACe meets these requirements with its HTCR radial trucks, high horsepower and quiet air-conditioned cabs. Many crews prefer to switch with such locomotives over the tried-and-true GP38s or MP15s. Absurd as this sounds, this is not a rare occurrence. But is this appropriate asset utilization? The answer is no. If low- or zero-emission solutions are in the future of railroad operations, managers will have to accept that future locomotive assets are going to be less fungible and more task-specific vehicles.
There are variations for this theme of three locomotive categories. Switcher BELs can have regenerative braking or power sharing with battery slugs. Local-service units can have on board charging from emissions-free HFCs as an alternative to ICE power. Hybrid locomotives can have a provision for 480-volt wayside charging. In the highway vehicle world, this is the equivalent to Plug-in Hybrid Electric Vehicles (PHEVs) of Toyota, Ford, Mazda, Audi and others. Local-service locomotives, with or without slugs, can have operator cabs on both ends where two locomotives are used. In short, there are many opportunities to optimize the solutions.
Yet, at the end of any large-scale or sustained drive for lower emissions, customized solutions for the three basic categories of locomotives are likely. This also means that cascading locomotives down from road service to local service to switching duties, which is already impractical, is no longer a practical best practice. This good news is, utilizing locomotives for the service for which they were intended will reduce fuel consumption and reduce emissions.
