Is it difficult to turn a metro that uses overhead catenary to third rail?

Question

Can it be done? If so how long would it take to switch to it on a line that's 14.5 kilometes (9 miles).

Answer 1

It would be possible to convert one to the other but in practice it is unlikely that overhead lines would be converted to 3rd rail today or vice-versa.

100 years ago the London, Brighton and South Coast Railway  (LBSCR) in the UK introduced suburban electric trains in London. They consisted of motor coaches with sufficient power to haul 2 or 3 passenger carriages. Other rail companies like the North Eastern Railway (NER) were experimenting with electric locomotives for freight trains. All these drew power from overhead lines.

This meant supplying the power in alternating current (AC) to the train which was then converted to direct current (DC) for use in the traction motors.

In the 1920's and 1930's the Southern Railway (which had been formed from merging the LBSCR with others in 1923) received massive government grants to develope a suburban/interurban rail system south of the Thames and decided to opt for the third rail system instead, feeding DC direct to the traction motors. It was also cheaper to build and maintain than the overhead wires.

Meanwhile the London Underground had begun electrification in 1890 and used a 3rd/4th rail system from the start.

Some London tram routes during the first half of the last century used a system called the 'conduit' in place of overhead wires. This consisted of a groove between the running rails which carried the current supply, picked up by the tram using a device called the 'plough' attached to the underside.

These 2 rail systems are still in use today and much the same as they were when originally built. London trams however had gone by 1952.

More modern electric rail systems have overcome the technical problems experienced with early overhead systems and so this is the supply system of choice for most electric rail routes.

To convert a line of 14.5 kilometres or 9 miles from overhead to third rail would not take very long - a few weeks from start to finish.