![Speed Restriction Signs (11343937544)](https://upload.wikimedia.org/wikipedia/commons/1/1c/Speed_Restriction_Signs_%2811343937544%29.jpg)
Rail speed limits in the United States are regulated by the
Federal Railroad Administration
The Federal Railroad Administration (FRA) is an agency in the United States Department of Transportation (DOT). The agency was created by the Department of Transportation Act of 1966. The purpose of the FRA is to promulgate and enforce rail saf ...
. Railroads also implement their own limits and enforce speed limits. Speed restrictions are based on a number of factors including
curvature
In mathematics, curvature is any of several strongly related concepts in geometry. Intuitively, the curvature is the amount by which a curve deviates from being a straight line, or a surface deviates from being a plane.
For curves, the canonic ...
,
signaling
In signal processing, a signal is a function that conveys information about a phenomenon. Any quantity that can vary over space or time can be used as a signal to share messages between observers. The ''IEEE Transactions on Signal Processing'' ...
,
track condition
Going (UK), track condition (US) or track rating (AUS) are the track surface of a horse racing track prior to a horse race or race meet. The going is determined by the amount of moisture in the ground and is assessed by an official steward on the ...
, and the presence of
grade crossings
A level crossing is an intersection where a railway line crosses a road, path, or (in rare situations) airport runway, at the same level, as opposed to the railway line crossing over or under using an overpass or tunnel. The term also ...
. Like
road speed limits in the United States, speed limits for
tracks and
trains
In rail transport, a train (from Old French , from Latin , "to pull, to draw") is a series of connected vehicles that run along a railway track and transport people or freight. Trains are typically pulled or pushed by locomotives (often know ...
are measured in
miles per hour
Miles per hour (mph, m.p.h., MPH, or mi/h) is a British imperial and United States customary unit of speed expressing the number of miles travelled in one hour. It is used in the United Kingdom, the United States, and a number of smaller cou ...
(mph).
Signal speeds
Federal regulators limit the speed of trains with respect to the signaling method used. Passenger trains are limited to 59 mph and freight trains to 49 mph on track without
block signal
Railway signalling (), also called railroad signaling (), is a system used to control the movement of railway traffic. Trains move on fixed rails, making them uniquely susceptible to collision. This susceptibility is exacerbated by the enormo ...
systems. (''See''
dark territory
Dark territory is a term used in the North American railroad industry to describe a section of running track not controlled by signals. Train movements in dark territory were previously handled by timetable and train order operation, but since t ...
.) Trains without "an automatic
cab signal,
automatic train stop
Automatic train stop or ATS is a system on a train that automatically stops a train if certain situations occur (unresponsive train operator, earthquake, disconnected rail, train running over a stop signal, etc.) to prevent accidents. In some scena ...
or
automatic train control
Automatic train control (ATC) is a general class of train protection systems for railways that involves a speed control mechanism in response to external inputs. For example, a system could effect an emergency brake application if the driver d ...
system "may not exceed 79 mph." The order was issued in 1947 (effective 31 Dec 1951) by the
Interstate Commerce Commission
The Interstate Commerce Commission (ICC) was a regulatory agency in the United States created by the Interstate Commerce Act of 1887. The agency's original purpose was to regulate railroads (and later trucking) to ensure fair rates, to eliminat ...
following a severe
1946 crash in Naperville, Illinois involving two
Chicago, Burlington & Quincy Railroad
The Chicago, Burlington and Quincy Railroad was a railroad that operated in the Midwestern United States. Commonly referred to as the Burlington Route, the Burlington, or as the Q, it operated extensive trackage in the states of Colorado, Illin ...
trains. Following the
1987 Chase, Maryland train collision, freight trains operating in enhanced-speed corridors have been required to have locomotive speed limiters to forcibly slow trains rather than simply alerting the operator with in-cab signals. The signal panel in the Maryland crash had been partially disabled, with a muted whistle and a missing light bulb.
Following the
2008 Chatsworth train collision in
California
California is a U.S. state, state in the Western United States, located along the West Coast of the United States, Pacific Coast. With nearly 39.2million residents across a total area of approximately , it is the List of states and territori ...
, a
federal law
Federal law is the body of law created by the federal government of a country. A federal government is formed when a group of political units, such as states or provinces join in a federation, delegating their individual sovereignty and many po ...
was enacted requiring
positive train control
Positive train control (PTC) is a family of automatic train protection systems deployed in the United States. Most of the United States' national rail network mileage has a form of PTC. These systems are generally designed to check that trains a ...
(PTC) to be implemented nationwide by 2015. After multiple deadline extensions, on December 29, 2020 PTC technology was announced by the FRA to be in operation on all required freight and passenger railroad route miles. While a primary goal of PTC is to prevent collisions, it also fulfills the FRA requirements for increased speeds in some cases. Several competing PTC technologies are used in different regions of the country.
Track classes
![CTA speed limit sign](https://upload.wikimedia.org/wikipedia/commons/6/6a/CTA_speed_limit_sign.jpg)
In the
United States
The United States of America (U.S.A. or USA), commonly known as the United States (U.S. or US) or America, is a country primarily located in North America. It consists of 50 states, a federal district, five major unincorporated territorie ...
, the
Federal Railroad Administration
The Federal Railroad Administration (FRA) is an agency in the United States Department of Transportation (DOT). The agency was created by the Department of Transportation Act of 1966. The purpose of the FRA is to promulgate and enforce rail saf ...
has developed a system of classification for track quality. The class of a section of track determines the maximum possible running speed limits and the ability to run passenger trains.
Curves
Assuming a suitably maintained track, maximum track speed through curves is limited by the "
centrifugal force
In Newtonian mechanics, the centrifugal force is an inertial force (also called a "fictitious" or "pseudo" force) that appears to act on all objects when viewed in a rotating frame of reference. It is directed away from an axis which is paralle ...
" which acts to overturn the train. To compensate for this force, the track is superelevated (the outer rail is raised higher than the inner rail). The speed at which the centrifugal force is perfectly offset by the tilt of the track is known as the balancing speed. Maximum speed can be found using the following formula, which provides an allowance for trains to operate above the balancing speed:
:
where:
:
is the amount in inches that the outside rail is
superelevated above the inside rail on a curve
:
is the amount in inches of unbalanced superelevation
:
is the
degree of curvature
Degree of curve or degree of curvature is a measure of curvature of a circular arc used in civil engineering for its easy use in layout surveying.
Definition
The degree of curvature is defined as the central angle to the ends of an agreed lengt ...
in degrees per
:
is given in
miles per hour
Miles per hour (mph, m.p.h., MPH, or mi/h) is a British imperial and United States customary unit of speed expressing the number of miles travelled in one hour. It is used in the United Kingdom, the United States, and a number of smaller cou ...
![Rail track lubricator](https://upload.wikimedia.org/wikipedia/commons/4/45/Rail_track_lubricator.jpg)
Normally, passenger trains run above the balancing speed, and the difference between the balancing superelevation for the speed and curvature and the actual superelevation on the curve is known as unbalanced superelevation. Track superelevation is usually limited to , and is often lower on routes with slow heavy freight trains in order to reduce wear on the inner rail. Allowed unbalanced superelevation in the U.S. is restricted to , though is permissible by waiver.
Tilting trains
A tilting train is a train that has a mechanism enabling increased speed on regular rail tracks. As a train (or other vehicle) rounds a curve at speed, objects inside the train experience centrifugal force. This can cause packages to slide ab ...
like the
Acela operate with even higher unbalanced superelevation, by dynamically shifting the weight of the train. The actual overturning speed of a train is much higher than the limits set by the speed formula, which is largely in place for passenger comfort. There is no hard maximum unbalanced superelevation for European railways, some of which have curves with over of unbalanced superelevation to permit high-speed transportation.
The allowed unbalanced superelevation will cause trains to run with normal flange contact. The points of wheel-rail contact are influenced by the
tire profile of the wheels. Allowance has to be made for the different speeds of trains. Slower trains will tend to make flange contact with the inner rail on curves, while faster trains will tend to ride outwards and make contact with the outer rail. Either contact causes
wear and tear
Wear and tear is damage that naturally and inevitably occurs as a result of normal wear or aging. It is used in a legal context for such areas as warranty contracts from manufacturers, which usually stipulate that damage from ''wear and tear'' w ...
and may lead to derailment if speeds and superelevation are not within the permitted limits. Many high-speed lines do not permit the use of slower freight trains, particularly with heavier
axle load
An axle or axletree is a central shaft for a rotating wheel or gear. On wheeled vehicles, the axle may be fixed to the wheels, rotating with them, or fixed to the vehicle, with the wheels rotating around the axle. In the former case, bearing ...
s. In some cases, the wear or friction of flange contact on curves is reduced by the use of
flange
A flange is a protruded ridge, lip or rim (wheel), rim, either external or internal, that serves to increase shear strength, strength (as the flange of an iron beam (structure), beam such as an I-beam or a T-beam); for easy attachment/transfer of ...
lubrication.
See also
*
Slow zone
In the United States, a slow zone is an area where a train is forced to slow down for either structural, construction, power, signal, or track problems. Slow zones limit a train to about . Notification to train crews is referred to as a "slow ord ...
*
Rail regulations in Canada
*
Railroad operations
*
Railway signalling
Railway signalling (), also called railroad signaling (), is a system used to control the movement of railway traffic. Trains move on fixed rails, making them uniquely susceptible to collision. This susceptibility is exacerbated by the enormou ...
References
{{DEFAULTSORT:Speed Limits In The United States (Rail)
Rail transport operations
Rail infrastructure in the United States
United States railroad regulation