Only a small portion of that 118 km will be in newly built tunnel and there will be relatively few newly built underground stations on Crossrail, which is why i

Only a small portion of that 118 km will be in newly built tunnel and there will be relatively few newly built underground stations on Crossrail, which is why it's much cheaper (underground stations are very expensive to build). Also, the use case for Crossrail is very different from the use case of the Second Avenue Subway.