What are the disadvantages of third rail system of track electrification?

A very high current must therefore be used to transfer adequate power to the train, resulting in high resistive losses, and requiring relatively closely spaced feed points (electrical substations). The electrified rail threatens electrocution of anyone wandering or falling onto the tracks.



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There are a variety of disadvantages associated with electric traction. They include high construction costs that can cause difficulties to use in areas with low traffic and the inflexibility due to overhead and third rail wires required by electric trains. Also, they are vulnerable when power is cut off.

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Because of mechanical limitations on the contact to the third rail, trains that use this method of power supply achieve lower speeds than those using overhead electric wires and a pantograph. Nevertheless, they may be preferred inside cities as there is no need for very high speed and they cause less visual pollution.

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On other systems, like the L, the third rail carries the positive charge, and the negative return is sent through one of the running rails.

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Andy Morris survives 625-volt zap after being pushed onto live third rail in drunken brawl.

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More common occurrences include low speed accidents in stations, depots and yards. Train collisions can have a number of causes: drivers passing signals at danger, faulty routing, speeding, division of trains, poor wheel-rail adhesion and technical and human errors in the signalling system.

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The main disadvantage of high-?speed trains, other than their slow speeds compared with air travel, is that they require a huge amount of infrastructure that must be built and maintained to extremely precise standards.

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Electric trains are superior to diesel trains for several reasons. They can accelerate and decelerate much more quickly, which reduces travel times between stations and allows more trains to be on the line at the same time. They are zero-emissions, so they're good for the climate and reduce local pollution.

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At the point of privatisation there was not enough revenue in the rail system to meet operating costs, capital investment and the claims of shareholders. Like most countries, Britain's rail system was and still is loss-making. To make up the revenue shortfall, the government introduced a system of public subsidies.

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Most of the railway was dismantled shortly after the war. Only the first 130 kilometres (81 mi) of the line in Thailand remained, with trains still running as far north as Nam Tok.

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Fuel combustion, track abrasion and freight leakages cause the most soil and plant contamination, because their emissions are neither chemically, or biologically degraded. Similarly, heavy metals found in the water bordering the tracks are often caused by leakages from petroleum products carried on the system.

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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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As a result, although rail transport has advantages such as high carrying capacity, economy, reliability and environmental impact, it also has some disadvantages such as limited flexibility, operating costs, necessity of intermodal connections and delivery time.

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