Train stop - AbsoluteAstronomy.com

Railway signalling

Railway signalling is a system used to control railway traffic safely, essentially to prevent trains from colliding. Being guided by fixed rails, trains are uniquely susceptible to collision; furthermore, trains cannot stop quickly, and frequently operate at speeds that do not enable them to stop...

system, a train stop or trip stop (sometimes called a tripper) is a train protection device that automatically stops a train

Train

A train is a connected series of vehicles for rail transport that move along a track to transport cargo or passengers from one place to another place. The track usually consists of two rails, but might also be a monorail or maglev guideway.Propulsion for the train is provided by a separate...

if it attempts to pass a signal

Railway signal

A signal is a mechanical or electrical device erected beside a railway line to pass information relating to the state of the line ahead to train/engine drivers. The driver interprets the signal's indication and acts accordingly...

when the signal aspect and operating rules prohibit such movement, or (in some applications) if it attempts to pass at an excessive speed.

Basic operation

The train stop system consists of two basic components: the trip stop mechanism, mounted on the ground adjacent to the rail

Rail tracks

The track on a railway or railroad, also known as the permanent way, is the structure consisting of the rails, fasteners, sleepers and ballast , plus the underlying subgrade...

, which basically consists of a spring-loaded trip arm and an electric motor

Electric motor

An electric motor converts electrical energy into mechanical energy.Most electric motors operate through the interaction of magnetic fields and current-carrying conductors to generate force...

or pneumatic cylinder in electro-pneumatic systems; and the train-mounted trip cock

Valve

A valve is a device that regulates, directs or controls the flow of a fluid by opening, closing, or partially obstructing various passageways. Valves are technically pipe fittings, but are usually discussed as a separate category...

that is connected directly or electrically to the train's braking system

Brake (railway)

Brakes are used on the cars of railway trains to enable deceleration, control acceleration or to keep them standing when parked. While the basic principle is familiar from road vehicle usage, operational features are more complex because of the need to control multiple linked carriages and to be...

.

The trip arm is up whenever the train should be automatically stopped. When it is safe for the train to proceed, the trip arm is lowered. This is a vital fail-safe

Fail-safe

A fail-safe or fail-secure device is one that, in the event of failure, responds in a way that will cause no harm, or at least a minimum of harm, to other devices or danger to personnel....

system. The motor drives the trip arm down only when the signalling system determines it is safe for the train to proceed; the spring

Spring (device)

A spring is an elastic object used to store mechanical energy. Springs are usually made out of spring steel. Small springs can be wound from pre-hardened stock, while larger ones are made from annealed steel and hardened after fabrication...

ensures that the trip arm is raised in all other situations (stop). If a train attempts to pass the signal with the trip arm in the raised position, the trip arm makes mechanical contact with the trip cock on the train, causing the train's brakes to be automatically applied and the train comes to
a stop.

Wayside trip arms are adjusted so that the trip arm rises to a point approximately 2½ inches (about 6 centimetres) above the top of the running rail when in the stop position, and lowers to approximately 1 inch (2.5 centimetres) below the top of the running rail when clear. Operating time is approximately two seconds.

Types of train stops

There are three types of train stops:

Trip stop - stops train trying to pass red signal
Timed train stop - stops train moving too fast
Fixed train stop - prevents any trains from passing a point

Trip stops

The trip arm is up whenever the signal is not displaying a proceed aspect. If the train tries to pass the signal, the train stop remains raised and trips the train to a stop. When the signal indicates it is safe to proceed (clear or caution), the trip arm is lowered, and the train is able to proceed without further hindrance. In some cases, train stops will not be lowered when the signals to which they apply are exhibiting proceed indications, e.g. when subsidiary signals are cleared, forcing trains to trip before proceeding, as a means of ensuring movements are conducted at safe speeds.

Timed train stops

With a timed train stop, the train stop stays raised until the approaching train has shunted a track circuit

Track circuit

A track circuit is a simple electrical device used to detect the absence of a train on rail tracks, used to inform signallers and control relevant signals.- Principles and operation :...

on the approach for a period of time corresponding to a set speed. If the train approaches at a speed higher than the set speed, the train stop remains raised and trips the train to a stop. If the train approaches at a speed equal or lower than the set speed, the train stop lowers before the train arrives, and the train is able to proceed without further hindrance.

Some timed train stops require the driver

Railroad engineer

A railroad engineer, locomotive engineer, train operator, train driver or engine driver is a person who drives a train on a railroad...

to acknowledge a stimulus before being lowered on a yellow signal.

For small fixed speed limit (15–20 km/h) simpler construction is also used. The trip arm rotates freely on a horizontal axis with counterbalance attached to its lower end. If train speed is low the arm will be rotated by the trip cock with small force without braking. But if its speed is high force will be large due to counterbalance inertia

Inertia

Inertia is the resistance of any physical object to a change in its state of motion or rest, or the tendency of an object to resist any change in its motion. It is proportional to an object's mass. The principle of inertia is one of the fundamental principles of classical physics which are used to...

, causing braking.

Fixed train stops

Fixed train stops are a type of stop that is immovable. They are positioned before a dead end track to stop a train before it reaches the end. They may also be used at the end of tracks where normal service trains should not pass such as the end of electrified territory (Hamilton, NSW

Hamilton railway station, New South Wales

-Hamilton Junction Signal Box:Hamilton Junction Signal Box is separated from Hamilton Station by Beaumont Street Level Crossing. The elegant Victorian signal box was built by McKenzie & Holland in 1897, making it one of the oldest surviving mechanical signal boxes in Australia, and also one of the...

) , and to test the automatic brake and tripgear of trains departing certain locations, e.g. storage sidings.

A fixed train stop that is the last trainstop on a running line in the reverse direction may, despite its name, be suppressed, as is the case with the associated "Fixed Signals" at Macarthur

Macarthur, New South Wales

Macarthur is a region in south-west of Sydney, in the state of New South Wales, Australia. The region includes the local government areas of the City of Campbelltown, Camden Council and Wollondilly Shire. It covers an area of 3,067 square kilometres and has a population of close to 240,000 residents...

, Turella, East Hills

East Hills, New South Wales

East Hills, a suburb of local government area City of Bankstown, is located 26 kilometres south-west of the Sydney central business district, in the state of New South Wales, Australia, and is a part of the South-western Sydney region....

, Emu Plains, Chatswood, Hornsby

Hornsby, New South Wales

* Highest Maximum Temperature: 42 °C* Lowest Maximum Temperature: 4.9 °C* Warmest Month: January* Coolest Month: July* Highest Precipitation: February* Lowest Precipitation: July-Notable residents:...

, Glenfield

Glenfield, New South Wales

Glenfield is a suburb of Sydney, in the state of New South Wales, Australia. Glenfield is located 40 kilometres south-west of the Sydney central business district, in the local government areas of the City of Campbelltown and the City of Liverpool...

, Homebush, etc. on the CityRail

CityRail

CityRail is an operating brand of RailCorp, a corporation owned by the state government of New South Wales, Australia. It is responsible for providing commuter rail services, and some coach services, in and around Sydney, Newcastle and Wollongong, the three largest cities of New South Wales. It is...

(Sydney) network. Suppression is needed because in Sydney, the rear triparm is always lowered, while in Melbourne, suppression is not needed as the rear triparm is raised.

Installations

In 1901 Union Switch and Signal Company developed the first automatic train stop

Automatic Train Stop

An automatic train stop is a system on a train that will automatically stop a train if certain situations happened to prevent accidents from happening....

system for the Boston Elevated Railway

Boston Elevated Railway

The Boston Elevated Railway was a precursor first to the Metropolitan Transit Authority in Massachusetts, now the Massachusetts Bay Transportation Authority, operating rapid transit, streetcars and buses in the Boston, Massachusetts area. It was formerly known as the West End Street Railway.The...

. This system was soon adopted by the New York City Subway

New York City Subway

The New York City Subway is a rapid transit system owned by the City of New York and leased to the New York City Transit Authority, a subsidiary agency of the Metropolitan Transportation Authority and also known as MTA New York City Transit...

and other transit systems in the United States. Similar systems were installed around this time on the London Underground

London Underground

The London Underground is a rapid transit system serving a large part of Greater London and some parts of Buckinghamshire, Hertfordshire and Essex in England...

system.

Because of its mechanical nature, the train stop has certain limitations in application. Severe snow and ice conditions, for example, could interfere with operation of the wayside trip arm. Its widest application, therefore, is on underground rapid transit

Rapid transit

A rapid transit, underground, subway, elevated railway, metro or metropolitan railway system is an electric passenger railway in an urban area with a high capacity and frequency, and grade separation from other traffic. Rapid transit systems are typically located either in underground tunnels or on...

lines, where conditions that might interfere with proper operation are readily controlled. The Toronto Transit Commission Subway

Toronto subway and RT

The Toronto subway and RT is a rapid transit system in Toronto, Ontario, Canada, consisting of both underground and elevated railway lines, operated by the Toronto Transit Commission . It was Canada's first completed subway system, with the first line being built under Yonge Street, which opened in...

is another system where train stops are used.

Train stops on London Underground lines are gradually being phased out in favour of ATP

Automatic Train Protection

Automatic Train Protection in Great Britain refers to either of two implementations of a train protection system installed in some trains in order to help prevent collisions through a driver's failure to observe a signal or speed restriction...

and distance-to-go signalling. They are standard equipment on all RailCorp metropolitan passenger lines in New South Wales and are also used in Melbourne, Australia.

Trackside installation

Berlin S-Bahn
Berlin S-Bahn
The Berlin S-Bahn is a rapid transit system in and around Berlin, the capital city of Germany. It consists of 15 lines and is integrated with the mostly underground U-Bahn to form the backbone of Berlin's rapid transport system...

rapid transit uses a metal bar at the height of the first bogie
Bogie
A bogie is a wheeled wagon or trolley. In mechanics terms, a bogie is a chassis or framework carrying wheels, attached to a vehicle. It can be fixed in place, as on a cargo truck, mounted on a swivel, as on a railway carriage/car or locomotive, or sprung as in the suspension of a caterpillar...

where the trip cock is placed. The metal bar (also named "Streckenanschlag" / track stop collar) folds away to allow passing.
Berlin U-Bahn small profile underground uses a metal stick hanging over track horizontally like a semaphore. The trip cock is on the roof of the first wagon (near the first door) almost looking like a lightning rod.
Berlin U-Bahn large profile underground uses a mushroom-shaped swivel next to the right rail that blocks by extending into the structure gauge
Structure gauge
The structure gauge, also called the minimum clearance outline, is the minimum height and width of tunnels and bridges as well as the minimum height and width of the doors that allow a rail siding access into a warehouse...

. The trip cock is mounted on the first bogie.
New York City Subway uses a T-shaped metal bar rising from the floor on the right side of the track for lines on the former IRT and the left side for the former BMT/IND. To allow passing it pivots down. A trip cock is mounted on the corner of the truck of each car. Placement depends on the division the train runs on; some rolling stock is equipped on both sides.
London Underground uses a square-shaped metal plate that functions similar to the New York Subway system.
Sydney
Sydney
Sydney is the most populous city in Australia and the state capital of New South Wales. Sydney is located on Australia's south-east coast of the Tasman Sea. As of June 2010, the greater metropolitan area had an approximate population of 4.6 million people...

now uses the London Underground type J trainstop called the JA, except that it is mirror-image mounted on the left hand side of the track instead of the right hand side.

Reverse direction

When trains operate in the reverse direction, they may "back trip" on train stops applying to the normal direction, which is a nuisance. This may be avoided in one of three ways:

In Melbourne, the rear trip is raised, but this runs the risk of runaways from terminal stations at high elevation;
In Sydney, the rear trip is lowered, and train stops in the opposite direction are "suppressed" so that they do not engage the rear trip.
In New York, when the signalling system clears motion in one direction (on bi-directional track or through an interlocking
Interlocking
In railway signalling, an interlocking is an arrangement of signal apparatus that prevents conflicting movements through an arrangement of tracks such as junctions or crossings. The signalling appliances and tracks are sometimes collectively referred to as an interlocking plant...

), it will automatically drive the stops which apply to the other direction. This is necessary because trip-cocks are located along the entire length of trains in New York, not just the lead car.