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This is less of a problem in trains consisting of two or more multiple units coupled together, since in that case if the train stops with one collector in a dead gap, another multiple unit can push or pull the disconnected unit until it can again draw power. There are a number of advantages including the fact there is no exposure of passengers to exhaust from the locomotive and lower cost of building, running and maintaining locomotives and multiple units. Thus both systems are faced with the same task: converting and transporting high-voltage AC from the power grid to low-voltage DC in the locomotive. When converting lines to electric, the connections with other lines must be considered. If through traffic is to have any benefit, time-consuming engine switches must occur to make such connections or expensive dual mode engines must be used. The overhead wires make the service "visible" even in no bus is running and the existence of the infrastructure gives some long-term expectations of the line being in operation. In theory, these trains could enjoy dramatic savings through electrification, but it can be too costly to extend electrification to isolated areas, and unless an entire network is electrified, companies often find that they need to continue use of diesel trains even if sections are electrified.

Electricity for electric rail systems can also come from renewable energy, nuclear power, or other low-carbon sources, which do not emit pollution or emissions. Power gaps can be overcome in single-collector trains by on-board batteries or motor-flywheel-generator systems. A problem specifically related to electrified lines are gaps in the electrification. Electric vehicles, especially locomotives, lose power when traversing gaps in the supply, such as phase change gaps in overhead systems, and gaps over points in third rail systems. The difference between AC and DC electrification systems lies in where the AC is converted to DC: at the substation or on the train. The higher power of electric locomotives and an electrification can also be a cheaper alternative to a new and less steep railway if train weights are to be increased on a system. The electric train can save energy (as compared to diesel) by regenerative braking and by not needing to consume energy by idling as diesel locomotives do when stopped or coasting.

The increasing demand for container traffic, which is more efficient when utilizing the double-stack car, also has network effect issues with existing electrifications due to insufficient clearance of overhead electrical lines for these trains, but electrification can be built or modified to have sufficient clearance, at additional cost. Some electrifications have subsequently been removed because of the through traffic to non-electrified lines. The type of modulation employed in a submarine cable can have a major impact in its capacity. The high power of electric locomotives also gives them the ability to pull freight at higher speed over gradients; in mixed traffic conditions this increases capacity when the time between trains can be decreased. Circuit breakers can be used as an alternative to fuses, but have significantly different characteristics. The same applies to the kind of push-pull trains which have a locomotive at each end. But if you were driving a manual transmission car, you would probably leave the car in the same gear the whole time.

Regenerative braking returns power to the electrification system so that it may be used elsewhere, by other trains on the same system or returned to the general power grid. The majority of modern electrification systems take AC energy from a power grid that is delivered to a locomotive, and within the locomotive, transformed and rectified to a lower DC voltage in preparation for use by traction motors. These systems could either use standard network frequency and three power cables, or reduced frequency, which allowed for return-phase line to be third rail, rather than an additional overhead wire. Allies execute dual assaults in Italy: The Allied landing at Anzio and the initial Allied assault on the Italian town of Cassino both took place in January 1944. Allied leadership hoped that the Anzio landing would bypass the Germans' formidable Gustav Line and divert and weaken German defenses at Cassino, the key position on the line. On "French system" HSLs, the overhead line and a "sleeper" feeder line each carry 25 kV in relation to the rails, but in opposite phase so they are at 50 kV from each other; autotransformers equalize the tension at regular intervals.

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