The major cost drivers the new stations, not the tunnels. The Second Avenue subway has 16 new stations; Crossrail is only building 10 new stations. That said,

The major cost drivers the new stations, not the tunnels. The Second Avenue subway has 16 new stations; Crossrail is only building 10 new stations. That said, it's not really a surprise that construction costs are cheaper in the UK. Mean wages are 40% higher in the US overall. That the major New York construction firms are deeply integrated with organized crime doesn't help, of course.