In practice, time spent traveling on certain modes (especially train, but also bus and car passengers) can sometimes be used to carry out some work, while time spent using certain other modes (especially car drivers, cyclists and walkers) cannot be used to carry out work. This means the value of travel time (and thus the value of travel time reductions) for modes where the employee could carry on doing some work is lower for employees already using any such mode. Conversely the value of travel time reductions for such modes for employees currently using a mode that does not allow carry out work (and who would switch mode) is larger.