The EMD F40PH is a four-axle 3,000–3,200 hp (2.2–2.4 MW) B-B diesel-electric locomotive built by General Motors Electro-Motive Division in several variants from 1975 to 1992. Intended for use on Amtrak's short-haul passenger routes, it became the backbone of Amtrak's diesel fleet after the failure of the EMD SDP40F. The F40PH also found widespread use on commuter railroads in the United States and with Via Rail in Canada. Additional F40PH variants were manufactured by Morrison-Knudsen and MotivePower between 1988 and 1998, mostly rebuilt from older locomotives.

Amtrak retired its fleet of F40PHs in the early-2000s in favor of the GE Genesis, but the locomotive remains the mainstay of Via Rail's long-distance trains and an image of the locomotive hauling The Canadian was featured on the Frontier series of the Canadian $10 bill. The F40PHs are still a common sight on many other commuter railroads throughout the United States. In addition, Amtrak has kept 22 of its F40PHs in use as Non-Powered Control Units.

Background
Amtrak inherited an aging and mechanically-incompatible fleet of diesel locomotives from various private railroads on its startup in 1971. The most modern locomotives remained in private hands for freight service, or to operate the various commuter services which, by law, did not pass to Amtrak. To replace these Amtrak ordered 150 EMD SDP40F locomotives, which began entering service in 1973. These were supplemented by 25 GE P30CHs which entered service in 1975. The SDP40F was a troubled design; problems with weight distribution led to a series of derailments in the mid-1970s. Meanwhile, the poor truck design of the P30CH (and the electric GE E60CP) curtailed further orders of that unit when Amtrak found itself needing more short- and medium-distance power in the spring of 1975.

Design
The design of the F40PH was based on the EMD GP40-2 freight road-switcher and shared that locomotive's turbocharged EMD 645E3 V16 cylinder, two-stroke, water-cooled diesel engine (prime mover). The prime mover developed 3,000 hp (2.2 MW) at 893 RPM. The main (traction) generator converts mechanical energy from the prime mover into electricity distributed through a high voltage cabinet to the traction motors. Each of the four traction motors is geared to a pair of driving wheels; the gear ratio determines the maximum speed of the locomotive. A standard F40PH has a gear ratio of 57:20, permitting a maximum speed of 103 mph (166 km/h). Some Amtrak F40PHs were delivered with a 56:21 gearing for 110 mph (177 km/h). The first 30 locomotives were built with a 1,500-US-gallon (5,700 l; 1,200 imp gal) fuel tank. Subsequent units were built with a 1,800-US-gallon (6,800 l; 1,500 imp gal) tank. Beginning with the EMD F40PH-2, introduced in 1985, the prime mover developed 3,200 horsepower (2.4 MW). Many of the original F40PHs were updated to match that output. The locomotives were 56 feet 2 inches (17.1 m) long. A standard F40PH weighs 260,000 lb (117,934 kg).

For passenger service the F40PH has another electrical alternator, the head-end generator. The HEP unit generates three-phase AC power at 480 V (500 kW on the first order, 800 kW on later units) for lighting, heating and air-conditioning the train. Originally, F40PHs powered the HEP alternator from the prime mover. From the head end to the train must be a constant frequency, and the prime mover had to turn at a constant 893 RPM while supplying head end power (even standing still, with the throttle in idle). Power to the traction motors was controlled by varying the field excitation of the main (traction) generator. On some later versions of the F40PH (and on many rebuilt F40s), a second small diesel engine at the rear of the locomotive powers the HEP alternator. In these engines, the prime-mover speed varies in the usual way. They can be identified by the diesel exhaust at the rear of the locomotive and by their quiet idle. Remaining F40s, with the constant-RPM prime movers, are noticeably louder.

In the initial design the battery box and air reservoirs were located forward of the fuel tank. In locomotives manufactured after 1977 these were relocated behind the tank. The battery box returned to its original location in the F40PH-2. The F40PH-2s delivered to Caltrain incorporated Southern Pacific Railroad-style headlights.

The designation "F40PH" stood for the following: "F" for the full-width cowl carbody, "40" as the locomotive is part of EMD's 40-series (based on the GP40-2 freight locomotive), "P" for passenger service, and "H" for head-end power.

History
Amtrak ordered its first 30 F40PHs on May 8, 1975; the first of the new locomotives entered service on April 9 the following year. Amtrak intended the locomotives for short routes such as the San Diegan in California and Northeast Corridor services in the then non-electrified portion between New Haven, Connecticut and Boston, Massachusetts. The long-distance routes were protected by the then-new EMD SDP40F, described by J. David Ingles in late 1975 as the "stars of Amtrak's long-distance trains". Two events led to a major change in thinking within Amtrak. The first was a sharp decline in the mechanical reliability of the EMD SDP40F, including several derailments. The second was the unusually harsh winter of 1976–1977, which sidelined many of Amtrak's aging steam-heated coaches. Amtrak suspended numerous routes and pressed the new HEP-equipped Amfleet I coaches, designed for short runs, into service. The F40PH, with its built-in HEP generator, was the natural choice to haul these trains.

As problems with the EMD SDP40F mounted, Amtrak adopted the F40PH as its long-term solution nationwide for diesel service. In the spring of 1977 Amtrak traded 40 SDP40Fs back to EMD; components including the prime mover were installed into an F40PH's frame. The 40 rebuilt locomotives were designated F40PHR and were identical to new-build F40PHs, incorporating the larger fuel tank and more powerful HEP generator which had become standard. Amtrak ultimately acquired 132 F40PHRs in this manner, which combined with new orders between 1975–1988, and the purchase of six GMD F40PHs from GO Transit in 1990, led to a fleet of 216 locomotives, the country's largest fleet.

The first commuter rail operator to order F40PHs was Chicago's Regional Transportation Authority (RTA), a forerunner to Metra, who ordered 74 between 1977–1983. Metra ordered 41 more between 1988–1992. Other agencies who bought the F40PH included the Massachusetts Bay Transit Authority (MBTA) (18), Caltrain (20), GO Transit (6), New Jersey Transit (17), and Via Rail (59). Finally, the rail construction firm Speno ordered four. In total EMD built 449 locomotives, including the F40PHR trade-ins.

The F40PH performed well for Amtrak; at the start of the 1990s only four had been retired due to wrecks and the locomotive was at the center of Amtrak's advertising. Trains magazine estimated that on average, each F40PH traveled as many as 175,000 miles (282,000 km) a year. Amtrak began replacing the F40PH with the GE Dash 8-32BWH in 1991, the GE P40DC in 1993 and the GE P42DC in 1996. All were retired by 2001 with the arrival of the last P42DC and their last regular assignment was on the Maple Leaf in December 2001.

The F40PH has continued to serve Via Rail into the 21st century; between 2007–2012 Via refurbished its entire fleet for CAD $100 million. The rebuild program included separate HEP generators, overhauled engines, a 3rd headlight addition, cab reconditioning, additional safety horns at the front, and repainting into the newer VIA scheme. A rebuilt locomotive, No. 6403, pulling the Canadian through the Rocky Mountains, was included on the back of the redesigned Canadian ten-dollar note in 2013 (the actual 6403 was later renumbered to 6459). As of 2018, VIA has 53 such locomotives in service. These locomotives are now supplemented by GE P42DC locomotives delivered in 200