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Double heading
Double heading
Double heading
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When double-heading a train, two locomotives are used at the same end—historically with separate crews.
A double-headed U.S. passenger train of the 1860s at Dale Creek Crossing near Sherman in southeastern Wyoming
A double-headed steam excursion train in Iowa, September 2006

In railroad terminology, double heading indicates the use of two locomotives at the front of a train,[1] each operated individually by its own crew. The practice of triple-heading involves the use of three locomotives. The practice of multi-heading involves the use of multiple locomotives and so on.

Double heading is most common with steam locomotives, but is also practised with diesel locomotives. It is not strictly the same practice as two or more diesel or electric locomotives working 'in multiple' (or 'multiple-working'), where both (or all) locomotives are controlled by a single driver in the cab of the leading locomotive.

Advantages

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Double heading is practised for a number of reasons:

  • In the UK it was usually to gain traction on steep inclines, twice the amount of driven wheels – twice the amount of grip.
  • The need for additional motive power when a single locomotive is unable to haul the train due to uphill grades, excessive train weight, or a combination of the two.
  • Double heading is also used on passenger trains when one locomotive could suffice but would not be fast enough to maintain the schedule.
  • More rarely, certain companies have used double-heading to guarantee a service when they have been aware of the poor quality of their locomotives, on the understanding that if one engine failed in service, the other would suffice to get the train to its destination.
  • Double heading is a useful practice on single lines even in the absence of a need for more power, as to double-head a train saves making a separate path for a spare engine; it can be repositioned using the traffic path occupied by the service train.
  • As double heading has become increasingly uncommon railway companies may advertise specially double-headed services as an attraction to enthusiasts; this occurs regularly but infrequently on the British mainline, whilst the Romney, Hythe & Dymchurch Railway in England advertises an annual day when all of its passenger trains are double-headed all day, both steam and diesel.
  • In the United Kingdom, double-heading is used to provide redundancy for all trains hauling nuclear flasks (usually to or from Sellafield, Cumbria). For security and safety reasons, trains carrying nuclear waste cannot be allowed to be left standing after a breakdown.
  • In the days when most trains were locomotive-hauled, double heading was frequently used to return engines to their home depot, or to another point on the railway network, by attaching them to a scheduled train. "Light engine" movements, with no train attached, are avoided where possible as it is difficult to find space in the timetable for them. This is exacerbated by the fact that light engines must run at reduced speed because they do not benefit from the braking power or stabilising effect of a following train.

Disadvantages

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Double heading requires careful cooperation between the engine crews, and is a skilled technique, otherwise one locomotive's wheels could slip, which could stall the train or even cause a derailment.

The risks of double heading as well as its costs (fuel and maintenance costs for the engines, wages for their crews) have led railroads to seek alternative solutions. Electrification has been used in many cases. The Milwaukee Road in the northern US was able to switch from triple-headed steam locomotives to a single electric locomotive. The costs of running extra steam locomotives were eliminated, and average train speeds increased because it was no longer necessary to attach and detach the locomotives. In Britain, the Midland Railway used to use double-heading often, because it built only small, light locomotives, which were often not powerful enough to haul the trains alone. Several accidents on the Midland system were indirectly caused by this 'small engine policy' and the resulting reliance on double-heading. Some were caused by trains stalling despite being double-headed, while others were caused by excessive light-engine movements as locomotives that had been used for double-heading returned to their depots (the Hawes Junction rail crash in 1910). When the Midland was absorbed into the London, Midland and Scottish Railway, this practice was stopped because it was uneconomical, and more powerful locomotives were built.

Special terminology

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Double heading A1 and A1X 'Terriers' Wooton and Freshwater running around the train at Wootton railway station, Isle of Wight Steam Railway

When a train formation includes two locomotives double-heading the service, they are commonly distinguished by the terms pilot engine for the leading locomotive, and train engine for the second locomotive. This should not be confused with the totally different procedure of adding a banking engine to the rear of a train to assist up a hill or away from a heavy start.

Great Western Railway

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For many years the Great Western Railway (GWR) of the United Kingdom often maintained a unique practice when double-heading was required, whereby if an extra locomotive was to be added to the front of a train for a particular section of line the second 'pilot' engine (called an 'assistant engine' in official GWR terminology) would be coupled "inside", or directly to the train, while the original 'train' engine would remain at the front of the formation (the reverse of normal practice). This was not universal practice on the GWR, with the company's regulations containing a complicated set of orders to determine whether an assistant engine should be placed inside or ahead of the train engine. These depended on the relative size and power of the two engines in question (larger assistant engines always went in front of the train engine), the wheel arrangement of the two engines, whether the engines in question were tank locomotives or not and whether the line being worked was a single upward gradient or contained any level sections or falling gradients. For instance, the GWR required that tank engines without leading bogies should always be coupled inside (i.e. between the other locomotive and its train) of tender engines, regardless of which was the train engine and which was the assistant, while the company's 2-6-2 tank engines could lead.

The GWR implemented these unusual restrictions to avoid having smaller, lower-power engines (especially tank engines) without leading bogies being propelled from behind by faster, more powerful engines since this was determined to be a major factor in a fatal and especially destructive derailment at Loughor in October 1904. Putting the smaller assisting engine between the more powerful one and the train was deemed to provide better stability at speed and under power for the assisting engine. Despite requiring time-consuming shunting operations each time an engine had to be added to or removed from a train under these rules, they remained in place on parts of the GWR until nationalisation in 1948.

See also

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References

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Revisions and contributorsEdit on WikipediaRead on Wikipedia

Double heading

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from Grokipedia
Double heading is a railroad operating practice in which two locomotives are employed to haul a single , providing additional power to manage heavy loads, steep gradients, or challenging topographical conditions. This technique, also known as double traction, enhances traction, reliability, and overall hauling capacity, particularly during the era from the 19th to mid-20th century. Historically, double heading emerged as railroads expanded across rugged terrains, with early mechanical implementations dating to 1883 by , followed by the first electric version in 1895 on the . It was commonly used on routes like the Union Pacific's or the Santa Fe lines in the American West, where pairs of steam engines, such as types, were coupled to pull freight or passenger consists that exceeded a single locomotive's capabilities. Notable examples include the Baltimore & Ohio's "Big Sixes" tackling Sand Patch Grade in 1951 and excursion runs like Railfair '81 featuring Union Pacific engines #8444 and #3985. In practice, double heading can take several forms, including tandem operation (where locomotives are synchronously controlled by one driver), pilot engine mode (with separate drivers for each unit), or bank engine assistance (pushing from the rear). While prevalent in the steam age, its use declined with the advent of diesel-electric locomotives in the mid-20th century, which allowed multiple-unit (MU) control for distributed power more efficiently. Today, it persists in specialized scenarios, such as heavy freight on upgraded tracks with reinforced couplers, as seen in operations by companies like Rail Cargo Group since 2017, where it can increase trailing loads by up to 50%.

Definition and History

Definition

Double heading is a railroad operating practice involving the attachment of two to the front of a train, each managed independently by its own crew of engineer and fireman (in the case of ), to augment the overall and hauling capacity. This configuration allows the combined power output to exceed that of a single , enabling the movement of trains that would otherwise be too heavy or demanding for one unit alone. Unlike related practices such as banking—where an assisting pushes from the rear, often without a to the —or triple heading, which employs three locomotives at the head end, double heading specifically utilizes exactly two lead locomotives for propulsion. It also contrasts with multiple-unit (MU) control systems in diesel-electric operations, where locomotives are linked electronically for unified control by a single crew, rather than independent operation. Mechanically, the locomotives are coupled in , with the lead unit connected directly to the first car of the and the trailing unit attached behind it, typically using standard drawbars or reinforced couplings to handle increased stresses. Brake control is centralized on the lead locomotive through a double-heading cock, a manually operated that transfers authority over the train's air system to the front unit, ensuring coordinated stopping while the trailing locomotive's brakes are applied independently for its own management. Throttle relies on close coordination between crews, often via signals, hand gestures, or visual of the lead unit's movements, with engineers adjusting power output to maintain even , prevent buff forces from slack action, and match speeds across varying grades. This practice finds primary application in scenarios demanding enhanced power, such as hauling heavy freight consists over extended distances, accelerating passenger up steep inclines where limits single-unit performance, or navigating routes with prolonged gradients that would otherwise require excessive time or multiple stops.

Historical Development

The practice of double heading, involving two locomotives pulling a single , originated in the early on American railroads, particularly on and freight lines where heavy loads and steep gradients posed challenges for single-engine operations. By the and 1840s, railroads in Pennsylvania's regions employed double heading to transport up grades, as early as the late on lines like the Hazleton Railroad. This early adoption addressed the limitations of initial steam locomotives, which had insufficient for demanding hauls. Technological constraints of steam locomotives, including low boiler pressures (typically 50-80 psi in the 1830s, rising to 100-130 psi by the 1850s) and adhesion issues on slippery rails or inclines, drove the widespread adoption of double heading around the 1850s in both Europe and North America. In Europe, British railways relied on double heading due to policies favoring smaller engines on lines like the Midland Railway, enhancing power without redesigning hardware. By the mid-19th century, the practice had become standard for freight and passenger services on major lines, including use during the Civil War era to manage increased tonnage. Double heading reached its peak from the late through the mid-20th century, becoming a common solution for heavy wartime logistics during and especially , when U.S. railroads handled record freight volumes. During this period, it was routinely used on transcontinental routes and industrial hauls, with examples including Santa Fe and Baltimore & Ohio operations in the and to maximize capacity amid material shortages. The introduction of diesel-electric locomotives and after the 1940s led to the decline of double heading, as these technologies provided superior power-to-weight ratios and reliability without needing multiple units for most tasks. In the U.S., numbers dropped from 39,881 in 1944 (91% of motive power) to 5,982 by 1955 (19% of motive power), rendering double heading obsolete for regular service by the ; it persisted only in rare excursion or heritage contexts into the 1980s. While primarily associated with steam, double heading principles were applied to early electric systems, with the first electric implementation in 1895 on the , following mechanical traction experiments in 1883 by .

Operational Benefits and Challenges

Advantages

Double heading substantially enhances a train's pulling capacity by combining the tractive efforts of two locomotives, effectively increasing the starting and sustained power output when similarly sized units are employed. This additive tractive effort enables railroads to haul significantly heavier loads than the capacity of a single locomotive, which was particularly vital during the steam era for freight operations in resource-intensive industries such as and . The increased power from double heading also improves performance on challenging terrain, allowing trains to maintain higher speeds on inclines where a single locomotive would struggle, thereby reducing transit times and improving overall schedule adherence on routes with varying . In terms of , distributing the workload across two locomotives mitigates stress on individual units, which can extend equipment longevity and support more economical transport of bulk commodities over long distances, though overall fuel consumption increases. Furthermore, double heading introduces a layer of through built-in ; if one experiences a mechanical failure, the second can sustain or facilitate a controlled stop, minimizing risks associated with power loss on the line. This reliability factor has been especially emphasized in high-stakes applications.

Disadvantages

Double heading, the practice of employing two locomotives to haul a single , incurs significant operational costs primarily due to the duplication of resources required for both engines. Fuel consumption increases compared to single-locomotive operations, as each demands its own supply of and , necessitating more frequent refueling stops and increasing overall resource management challenges. Additionally, the need for separate crews—each consisting of an and fireman, among others—doubles labor expenses, including wages and compliance with railway labor regulations on working hours and crew qualifications. These factors contributed to higher per-trip expenditures, making double heading less economical for routine services despite its utility for heavy loads. Coordination between the two locomotives introduces complexities that elevate risks and potential for incidents. Precise of speed, , and braking is essential to avoid mismatched efforts, which could cause wheel slippage, excessive strain, or even derailments if communication fails—often relying on manual signals like whistles rather than modern integrated systems. Historical operations highlighted these vulnerabilities, with the added power output amplifying stresses on the train consist and infrastructure, though specific incident rate comparisons to single-locomotive runs remain documented primarily through anecdotal railway reports rather than comprehensive statistical analyses. Maintenance demands further compound the logistical drawbacks of double heading. The intensified forces from dual locomotives accelerate wear on couplings, drawbars, and track components, requiring more frequent inspections and repairs to prevent failures. Scheduling two locomotives and their s also complicates turnaround times and availability, straining depot resources and contributing to inefficiencies in overall operations. Regulatory and environmental considerations have historically and increasingly undermined the viability of double heading. The requirement for additional personnel raises compliance costs with labor laws governing rest, , and protocols, while the elevated use results in higher emissions of particulates and greenhouse gases from steam operations. These issues, combined with the advent of diesel-electric locomotives in the mid-20th century that enable multiple-unit control with a single , hastened the decline of double heading in favor of more efficient, lower-emission technologies.

Terminology and Procedures

Special Terminology

In railway operations, the practice of double heading is commonly referred to synonymously as a "doubleheader," denoting the configuration where two locomotives are coupled at the front of a train to provide additional power. The leading locomotive in this arrangement is termed the "lead engine," responsible for primary control of the train's movement, braking, and signaling, while the second locomotive is known as the "trailing engine," which contributes propulsion but operates under the direction of the lead unit. A key distinction exists between double heading and related positional configurations, such as the use of a "pusher" , which is positioned at the rear of the to provide assistive , particularly on steep grades or with heavy loads, rather than pulling from . Unlike double heading, where both locomotives face forward and share the pulling effort, a pusher operates in a pushing mode and requires separate coordination for braking and communication to ensure safe integration with the train consist. In some regulatory contexts, pushers fall under "helper service," mandating visual inspections of brakes and communication devices like the Helper Link for operational reliability. Regional variations in terminology appear in historical practices, particularly between British and American railways. In British usage, "double heading" typically describes the overall practice, with the forward locomotive occasionally designated as the "pilot engine" to assist the primary "train engine" in maintaining schedule on demanding routes, a term less commonly applied in American contexts where "doubleheading" or simply "double-header" prevails without the "pilot" distinction. American terminology aligns closely but emphasizes the lead and trailing roles in federal standards, reflecting standardized safety protocols for multiple locomotive consists. Related concepts include the preference for matching locomotive classes in double heading, such as those with identical wheel arrangements (e.g., 4-8-4 configurations), to ensure balanced , synchronized , and reduced stress on couplings and track infrastructure. Mismatched pairs were avoided when possible due to challenges in power distribution and handling stability, though they occurred in emergencies or resource constraints.

Operational Procedures

Double heading operations commence with meticulous preparation to ensure the safe coupling and synchronization of multiple locomotives. The locomotives are mechanically connected using standard drawbar or coupler systems, with steam-era practices often positioning the trailing locomotive directly behind the lead without intervening cars. For diesel-electric units, additional steps include connecting air brake hoses and, if applicable, multiple-unit (MU) control cables to facilitate coordinated throttle and brake responses, although traditional double heading relies on independent crew operation rather than full MU synchronization. Pre-trip inspections are mandatory, encompassing visual checks of the coupling mechanism for secure attachment, verification of air line continuity, and brake system functionality; Federal Railroad Administration (FRA) guidelines require a specific test where the controlling locomotive applies a 20-psi brake pipe reduction to confirm that trailing units' brakes activate properly, with any inoperative systems necessitating repair or removal from service. Once coupled and inspected, control protocols emphasize clear communication and sequential actions between crews to maintain train integrity. The engineer on the lead assumes primary control of the train-line , while trailing engineers independently manage their locomotive's for and apply independent only as directed or in emergencies. Coordination occurs through established signals: in operations, crews use codes, bell signals, or visual cues from the lead locomotive to match power output and braking; modern diesel configurations supplement these with radio communications for real-time adjustments. The trailing locomotive typically initiates or actions 1-2 seconds after the lead to account for slack in the , preventing abrupt jerks or risks. Route-specific adaptations are critical to handle varying terrain safely during double heading. On ascending grades, both locomotives apply full power in unison, with the lead engineer signaling increases to maintain momentum; descending grades require careful braking procedures, where trailing units contribute additional retarding force to share the load and avoid overheating on the lead locomotive. For curves, speed is restricted based on the radius and superelevation to minimize lateral forces, with engineers reducing velocity progressively to ensure the trailing unit does not push excessively against the lead. All double heading procedures must adhere to stringent safety regulations to protect crews and infrastructure. , compliance with 49 CFR § 232.219 mandates that the controlling locomotive's operate the , with qualified personnel on helper units receiving explicit instructions for their roles, and requires a Class III test if control transfers mid-journey. Where helper link devices are used for remote communication with end-of-train signaling, these must alert operators to signal loss exceeding 25 seconds and undergo annual calibration testing, with records maintained for verification. Crew training is enforced under FRA standards in 49 CFR Part 240, ensuring all are certified and familiar with double heading protocols, including emergency separation procedures.

Notable Historical Examples

Great Western Railway

The Great Western Railway (GWR) employed double heading extensively for its express passenger services, particularly as train loads grew heavier in the early 20th century, with practices peaking during the 1920s and 1930s under the locomotive designs of and . Churchward's 4-6-0 "Saint" and "Star" classes laid the groundwork for handling increased tonnage, while Collett's subsequent "Castle" and "King" classes further optimized performance on demanding routes, often reducing but not eliminating the need for dual locomotives on gradients. A key application was on the (often referred to as the Cornish Riviera Limited in its early years), where double heading enabled the hauling of loads over 400 tons—such as 505 tons with a class locomotive—across the steep Devon banks, including the 2-mile Hemerdon incline at 1 in 42. Assistance was provided if the train exceeded 375 tons, with pilot engines sometimes assisting over the Dainton and Rattery summits en route to Plymouth. and class engines, weighing up to 135 tons and operating at 250 psi boiler pressure, were typically assigned to these duties for their power output. The GWR innovated in "double engine working" by matching locomotives like a leading "" class with a trailing "" class, ensuring synchronized operation for heavy expresses; this pairing, exemplified by engines such as No. 6024 King Edward I and No. 5029 , maximized while adhering to the railway's broad constraints. Such configurations were standard for non-stop runs from London Paddington to Plymouth (225.5 miles in 4 hours), minimizing delays on inclines where single engines might stall. The GWR's refined double heading techniques carried over into British Railways' Western Region after in 1948, informing load management and crew coordination on inherited routes like the main line.

Other Railways

In , double heading was a common practice for handling heavy freight, particularly on the system during the 1880s. The Pittsburgh, Fort Wayne and Railway, a key PRR serving regions, routinely employed double-headed light locomotives on freight trains to increase hauled amid competitive low rates, enabling up to 60-car consists with reduced crew compared to separate sections. This approach was essential for traffic over undulating terrain in and . During , the employed its Big Boy articulated locomotives for heavy transcontinental freights across the Overland Route, addressing wartime demands over steep grades like the Wasatch Mountains in and . Designed for 3,600-ton loads, Big Boys generally operated singly to replace prior double-heading practices but occasionally required helper engines for maximum wartime tonnage, highlighting the challenges of long-distance heavy freights even with advanced steam power. Beyond and , double heading was adapted on colonial-era railways in challenging terrains to overcome steep inclines without extensive regrading. Comparatively, double heading prevailed with rigid-frame locomotives on lighter grades but gave way to articulated designs like the Big Boy, which minimized the need for multiples by concentrating power in a single flexible unit. The practice declined sharply in the post-diesel era from the onward, as diesel-electric locomotives enabled seamless multiple-unit operation via standardized electrical controls, eliminating steam's synchronization issues and reducing crew demands for heavy hauls.

References

  1. https://www.american-rails.com/doublehead.html
  2. https://blog.railcargo.com/en/artikel/eisenbahn-einfach-erklaert-doppeltraktion
  3. https://www.law.cornell.edu/cfr/text/49/236.729
  4. https://www.thehopkinthomasproject.com/TheHopkinThomasProject/TimeLine/IndustrialRevAmerica/Railroads/BeaverMeadowRR/HeydingerSegments/HeydingerSeg8.htm
  5. https://npshistory.com/publications/stea/shs/chap2.htm
  6. https://playingtrains.wordpress.com/2018/08/04/small-engine-policy/
  7. https://www.nps.gov/parkhistory/online_books/steamtown/shs5.htm
  8. https://history.howstuffworks.com/american-history/post-war-railroads.htm
  9. https://www.merriam-webster.com/dictionary/double-head
  10. https://railroads.dot.gov/sites/fra.dot.gov/files/2020-05/MPEComplianceManual2013.pdf
  11. http://igg.org.uk/rail/7-fops/fo-intro.htm
  12. http://www.railway-technical.com/trains/rolling-stock-index-l/diesel-locomotives/us-locomotive-mu-control.html
  13. https://www.ecfr.gov/current/title-49/subtitle-B/chapter-II/part-232/subpart-C/section-232.219
  14. https://www.trains.com/trn/train-basics/abcs-of-railroading/how-railroads-design-grades-and-curves/
  15. https://www.ecfr.gov/current/title-49/subtitle-B/chapter-II/part-240
  16. https://www.keymodelworld.com/article/great-western-railway-collett-king-4-6-0
  17. https://www.railwaywondersoftheworld.com/cornish-riviera-express.html
  18. https://www.youtube.com/watch?v=z3W0RXapUpU
  19. http://www.prrths.com/newprr_files/Hagley/PRR1885.pdf
  20. https://www.american-rails.com/big.html
  21. https://americanbusinesshistory.org/the-unsung-20th-century-technology-that-disrupted-an-industry/
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