How Much Of The Central Line Is Underground?
Total track length is 91.4 miles (147.1 km), of which 32.8 miles (52.8 km) is in tunnel; this track is electrified with a four-rail DC system: a central conductor rail is energised at −210 V and a rail outside the running rail at +420 V, giving a potential difference of 630 V. How much of …