I think a lot will depend on maintenance and staff costs. If those costs are kept low then there will be little marginal cost per additional mile travelled.

I think a lot will depend on maintenance and staff costs. If those costs are kept low then there will be little marginal cost per additional mile travelled. In that scenario it would make sense to keep the tunnels as heavily utilised as possible by heavily cutting prices when traffic is low. Perhaps we will see freight running at night or even trash being moved out of cities. Having a low cost option could create new opportunities that have not been considered yet and help pay the bills. Running constant traffic twenty four hours per day changes things.