DC systems (especially third-rail systems) are limited to relatively low voltages and this can limit the size and speed of trains and cannot use low-level platform and also limit the amount of air-conditioning that the trains can provide. This may be a factor favouring overhead wires and high-voltage AC, even for urban usage. In practice, the top speed of trains on third-rail systems is limited to 100 mph (160 km/h) because above that speed reliable contact between the shoe and the rail cannot be maintained.
డిసి సిస్టమ్ రైళ్లలో వేగం 100 మైళ్ల పరిమితిని మించితే ఏది నమ్మదగినదిగా మారదు?
contact between the shoe and the rail