If the workers really are producing "substantially more" value for the economy, they are probably underpaid in the first place, or the specific train line/project is a bad investment (too expensive).
Workers always earn less than the value they make for a useful business under capitalism (and that's before taxes, which don't necessarily require or imply capitalism). There's always a point where a cost to a worker exceeds the value to that worker, but doesn't exceed the value to society of facilitating that worker's labour.
There are edge cases, but in general inhibiting the ability of workers to work (e.g. by making it expensive to get there, or expensive live near enough to the work, fail to allow them to be healthy enough to do the work, make it hard to take care of children while working, restrict access to or quality of education etc) is not good for a society built on work.
There are edge cases, but in general inhibiting the ability of workers to work (e.g. by making it expensive to get there, or expensive live near enough to the work, fail to allow them to be healthy enough to do the work, make it hard to take care of children while working, restrict access to or quality of education etc) is not good for a society built on work.