<Tr> <Th> Number of stations </Th> <Td> 270 served (260 owned) </Td> </Tr> <Tr> <Th> Daily ridership </Th> <Td> 5 million </Td> </Tr> <Tr> <Th> Annual ridership </Th> <Td> 1.379 billion (2016 / 17) </Td> </Tr> <Tr> <Th> Website </Th> <Td> London Underground </Td> </Tr>

What was the purpose of the underground rail road