Why do subway tracks spark?

Under acceleration, the train is drawing significant amounts of current from the wire to power, so if for any reason contact between the two is lost (even briefly), you'll see significant amounts of arcing as the current attempts to maintain the circuit.



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The sparks between overhead wire and pantograph occur when the contact is lost for a moment because the train is shaking or in winter when ice builds up on the wire.

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A few early subways used steam engines, but in most existing subways, the trains, tunnel lights and station equipment all run on electricity. Overhead wires or an electrified rail known as the third rail supplies power to the trains.

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Why do we feel jerks in train? This is due to the inertia, which oppose any change in its state. When train is at rest our body remains at rest. When train starts moving, due to inertia of rest it oppose the change and wants to be at rest, so we feel sudden jerk.

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The number of route miles electrified in these years was answered to a written question in parliament. In November 2019 the annual statistics for route miles electrified was published by the DfT and shows that 38% of the UK network is now electrified.

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Its primary purpose is to alert persons and animals to an oncoming train, especially when approaching a level crossing. They are often extremely loud, allowing them to be heard from great distances. They are also used for acknowledging signals given by railroad employees, such as during switching operations.

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Trains cannot collide with each other if they are not permitted to occupy the same section of track at the same time, so railway lines are divided into sections known as blocks. In normal circumstances, only one train is permitted in each block at a time. This principle forms the basis of most railway safety systems.

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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.

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This is why birds do not die from landing on power lines, and subway rats do not get electrocuted even if they run across the third rail; they are not bridging the energized wire or rail to a grounded part of the structure.

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The metaphor comes from the high-voltage third rail in some electric railway systems. This third rail, used to power trains, usually results in the death by electrocution of anyone who comes into direct contact with it.

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While fatalities from train derailments are rare, derailments themselves are actually quite common. From 1990, the first year the BTS began tracking derailments and injuries on a yearly basis, to 2022, there have been 55,741 accidents in which a train derailed. That's an average of 1,689 derailments per year.

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A derailment of a train can be caused by a collision with another object, an operational error (such as excessive speed through a curve), the mechanical failure of tracks (such as broken rails), or the mechanical failure of the wheels, among other causes.

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