|
Overlap (railway Signalling)
An overlap in railway signalling is the length of track beyond a stop signal that is proved to be clear of vehicles in the controls of the previous signal, as a safety margin. Overview Enough braking distance is provided to allow a train to comfortably stop at the stop signal, but should it fail to do so for any reason (fog, smoke, slippery rails, brake failure, inattention by driver, etc.) there is still some distance to allow the train to stop short of any obstruction, such as another train. Length The length of an overlap may be a nominal length, or else calculated on the full emergency braking distance for the gradients and speeds for that particular section of line. Two signal protection If the overlap is long enough to extend from one stop signal to the next, then the effect is to provide two signal protection (or "double blocking"), with the first signal having a full overlap, and the second signal having a short overlap. With two signal protection, only one trac ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Railway Signal
A railway signal is a visual display device that conveys instructions or provides warning of instructions regarding the driver’s authority to proceed. The driver interprets the signal's indication and acts accordingly. Typically, a signal might inform the driver of the speed at which the train may safely proceed or it may instruct the driver to stop. Application and positioning of signals Originally, signals displayed simple stop or proceed indications. As traffic density increased, this proved to be too limiting and refinements were added. One such refinement was the addition of distant signals on the approach to stop signals. The distant signal gave the driver warning that they were approaching a signal which might require a stop. This allowed for an overall increase in speed, since train drivers no longer had to drive at a speed within sighting distance of the stop signal. Under timetable and train order operation, the signals did not directly convey orders to the ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Braking Distance
Braking distance refers to the distance a vehicle will travel from the point when its brakes are fully applied to when it comes to a complete stop. It is primarily affected by the original speed of the vehicle and the coefficient of friction between the tires and the road surface, and negligibly by the tires' rolling resistance and vehicle's air drag. The type of brake system in use only affects trucks and large mass vehicles, which cannot supply enough force to match the static frictional force. The braking distance is one of two principal components of the total stopping distance. The other component is the reaction distance, which is the product of the speed and the perception-reaction time of the driver/rider. A perception-reaction time of 1.5 seconds, and a coefficient of kinetic friction of 0.7 are standard for the purpose of determining a bare baseline for accident reconstruction and judicial notice; most people can stop slightly sooner under ideal conditions. Braking ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Slippery Rail
Slippery rail, or low railhead adhesion, is a condition of railways (railroads) where contamination of the railhead reduces the traction between the wheel and the rail. This can lead to wheelslip when the train is taking power, and wheelslide when the train is braking. One common cause of contamination is fallen leaves that adhere to the railhead (top surface) of railway tracks. The condition results in significant reduction in friction between train wheels and rails, and in extreme cases can render the track temporarily unusable. In Britain, the situation is colloquially referred to as "leaves on the line". Low adhesion caused by weather Railhead contamination caused by weather conditions can occur at any time of year. The leaf fall season causes the most disruption to rail operations. In heavily deciduous forested areas like the American Mid-Atlantic states, New England, many parts of Europe including the UK, and Southern Ontario, Canada, the problem can arise. Where the l ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Brake
A brake is a mechanical device that inhibits motion by absorbing energy from a moving system. It is used for slowing or stopping a moving vehicle, wheel, axle, or to prevent its motion, most often accomplished by means of friction. Background Most brakes commonly use friction between two surfaces pressed together to convert the kinetic energy of the moving object into heat, though other methods of energy conversion may be employed. For example, regenerative braking converts much of the energy to electrical energy, which may be stored for later use. Other methods convert kinetic energy into potential energy in such stored forms as pressurized air or pressurized oil. Eddy current brakes use magnetic fields to convert kinetic energy into electric current in the brake disc, fin, or rail, which is converted into heat. Still other braking methods even transform kinetic energy into different forms, for example by transferring the energy to a rotating flywheel. Brakes are generally ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Track Circuit
A track circuit is an electrical device used to prove the absence of a train on rail tracks to signallers and control relevant signals. An alternative to track circuits are axle counters. Principles and operation The basic principle behind the track circuit lies in the connection of the two rails by the wheels and axle of locomotives and rolling stock to short an electrical circuit. This circuit is monitored by electrical equipment to detect the absence of the trains. Since this is a safety appliance, fail-safe operation is crucial. Hence the circuit is designed to indicate the presence of a train when failures occur. On the other hand, false occupancy readings are disruptive to railway operations and must be minimized. Track circuits allow railway signalling systems to operate semi-automatically, by displaying signals for trains to slow or stop in the presence of occupied track ahead of them. They help prevent Train dispatcher, dispatchers and Manual block, operators from ca ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Train Protection System
A train protection system is a railway technical installation to ensure safe operation in the event of human error. Development Train stops The earliest systems were train stops, as still used by the New York City Subway, the Toronto subway, the London Underground, the Moscow Subway (only on the older lines) and the Berlin S-Bahn. Beside every signal is a moveable arm. If the signal is red, levers connected to valves on any passing train hit the arm, opening the brake line, applying the emergency brake, If the signal shows green, the arm is turned away from the levers and there is no contact. The Great Western Railway in the UK introduced its 'automatic train control' system in the early years of the 20th century. Each distant signal had before it a ramp between the running rails. If the signal showed green, the ramp was energised with a low voltage current which was passed to the locomotive when a shoe came into contact with the ramp. A bell rang in the locomotive's cab t ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
