I
ICC	The Interstate Commerce Commission. This agency, until 1995, regulates most forms of surface transportation, and approves the instituting and discontinuing of railroad services. In 1995, the ICC was dissolved, and it's duties conferred to the Surface Transportation Board.
Idler	An unloaded flatcar placed before or after a car from which oversize machinery, pipe, or other material projects.
IHC	International Hobby Corporation. A Model Railroad Manufacturer.
In	A trainman who is at the home terminal and off duty is in.
In The Clear	A train is in the clear when it has passed over a switch and frog so far that another train can pass without damage.
In The Color	Train standing in the signal block waiting for a clear board.
In The Ditch	Wrecked or derailed.
In The Hole	Train on a siding waiting for another train to pass.
IND	INDependent City Subway - subdivision B-2 of the New York City Transit Authority (NYCTA) subway system.
Independent Application and Release Control	Controls independent brakes on multiple locomotives from a single control.
Indian Valley Line	An imaginary railroad "at the end of the rainbow," on which you could always find a good job and ideal working conditions. (Does not refer to the former twenty-one-mile railroad of that name between Paxton and Engels, Calif.) Boomers resigning or being fired would say they were going to the Indian Valley. The term is sometimes used to mean death or the railroader's Heaven. See Big Rock Candy Mountain.
Indicators	Illuminated signs on the engine and caboose that display the number of the train.
Industrial Locomotive	A small locomotive used on an industrial railroad for switching.
Industrial Railroad	A small railroad usually operated within a factory or industrial complex. These railroads are also used to move freight between an industrial complex and a nearby common carrier.
Industrial Track	A track other than a main track, running track, siding, or yard track, upon which movements must be made at Restricted Speed.
Initial Station	The first station on each subdivision from which a train is authorized to occupy the main track.
Inspection Car	Self-propelled service vehicle used for inspecting track.
Interchange	A track on which various cars are delivered or received from one railroad to another, also the point where passengers or freight are exchanged between trains.
Interline Traffic	Goods that are transported to their final destination by more than one rail company.
Interlocking	A mechanical or electrical signaling system that ensures that only one train at a time is allowed to move through a junction.
Interlocking Appliances	The parts of an interlocking that are capable of movement (i.e. switches, derails, locks, movable point frogs, movable bridges, etc.).
Interlocking Limits	The tracks between the opposing home signals of an interlocking.
Interlocking Signals	The fixed signals of an interlocking.
Interlocking Station	A location from which an interlocking is operated.
Intermodal Service	Freight moving via at least two different modes of transport. Intermodal service generally involves the shipment of containers and trailers by rail, truck, barge or ship.
Interurban	An electrically operated transit system linking a series of town to each other, or two a larger urban area. built to a heavier standard than trolley systems, they sometimes handled freight as well.
Inverse Gradient	The temporary condition when the brake pipe pressure is higher at the rear of the train than at the head end of the train (for example, at the beginning of a service brake application).
Iron	Rails.
Iron Horse	Slang for locomotive.
Iron Skull	Boilermaker.
IRT	Inter-boro Rapid Transit - subdivision A of the New York City Transit Authority (NYCTA) subway system.
Island	A section of track which incorporates a highway crossing.
Island Platform	A passenger platform with tracks on both sides. Pedestrian access is often by overpass or tunnel.
Ivory Tower	The main control room where the TMD (Train Movement Directors) are based.