Plain-English definitions of the railroad and steam locomotive terms you will hear around Big Boy 4014.
New to railroads? These are the terms that come up most when people talk about Big Boy 4014.
- Articulated
- A locomotive whose frame is hinged so it can bend around curves. The Big Boy is articulated.
- Boiler
- The tank in which water is heated into steam. Big Boy's runs at 300 psi.
- Caboose
- A crew car at the end of a freight train, mostly replaced by end-of-train devices.
- Consist
- The list of locomotives and cars that make up a train.
- Doubleheader
- A train pulled by two locomotives. 4014 and 844 doubleheaded on the 2019 trip.
- Driver (driving wheel)
- A large powered wheel connected to the pistons. Big Boy has 16, each 68 inches tall.
- Firebox
- The chamber at the rear of the boiler where fuel is burned.
- Grate area
- Floor area of the firebox where the fire sits. Big Boy's is 150 square feet.
- Heritage fleet
- Union Pacific's collection of historic locomotives kept operational for special trains.
- Helper
- An extra locomotive added to a train to climb a steep grade. Big Boys were built to reduce the need for helpers.
- Highball
- A signal or word meaning proceed. See What Railroaders Mean by “Highball”.
- Leading truck
- The unpowered wheels at the front that guide the locomotive into curves.
- Mallet
- A type of articulated steam locomotive with a hinged front engine.
- Pilot
- The front-mounted frame (sometimes called a cowcatcher) on a locomotive.
- Revenue service
- Hauling paying freight or passengers, as opposed to excursion or display.
- Sherman Hill
- The grade west of Cheyenne, Wyoming, where Big Boys worked. See Best Places to Photograph Big Boy.
- Steam shop
- The facility where steam locomotives are maintained. Union Pacific's is in Cheyenne.
- Tender
- The car behind the locomotive carrying fuel and water. Big Boy's holds 25,000 gallons of water.
- Tractive effort
- The pulling force a locomotive can exert. Big Boy's was 135,375 lb as built.
- Trailing truck
- The unpowered wheels at the rear that support the firebox.
- Wheel arrangement (Whyte notation)
- A shorthand for wheel counts. A 4-8-8-4 is a Big Boy. See Why Big Boy Has a 4-8-8-4 Wheel Arrangement.
- Whistle stop
- A brief stop at a town so people can see the train. 4014 made dozens in 2026.
- Display day
- A scheduled event where the public can see a locomotive stopped, sometimes up close.
Specs in detail: Big Boy 4014 Specifications Explained. Wheel layouts: Why Big Boy Has a 4-8-8-4 Wheel Arrangement. Photo tips: Best Places to Photograph Big Boy. Back to the The Complete Guide to Union Pacific Big Boy 4014.
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Keep Reading in the Big Boy 4014 Knowledge Hub
- Big Boy 4014 Specifications Explained
- Why Big Boy Has a 4-8-8-4 Wheel Arrangement
- What Railroaders Mean by “Highball”
- Best Places to Photograph Big Boy
Start with the complete guide to Big Boy 4014 for the full overview.