A positive effect of demixing on the energy efficiency of train operation is to be expected since demixing improves traffic fluidity by avoiding train stops or decelerations caused by speed differences.

There are however different effects brought about by demixing that have to be clearly distinguished:

1. Scheduled stops on the way due to slower trains letting pass faster trains are clearly reduced in a demixed infrastructure.
2. Unscheduled stops due to delayed trains impeding other trains may be reduced by demixing (cf. Figure 2).
3. Increased train density in a demixed infrastructure with raised capacity may increase number of train conflicts due to delays.

Figure 2: Schematic visualization of effect of train delys in mixed vs. demixed infrastructure (simplified)

Source: IZT

Effects 1 and 2 reduce the probability of train stops outside stations in a demixed infrastructure (as compared to the mixed case), effect 3 points in the opposite direction. It is very difficult to make a general statement on the dominance of one effect over the other and the total net effect.

Experts however tend to assume that effects 2 and 3 compensate each other yielding a zero net result. Effect 1 could then slightly improve overall “stopping statistics”.

Conclusion

Energy efficiency effects through demixing depend strongly on the individual network situation and trains densities. In most cases, the net effect will rather be a small positive one. It will however be extremely difficult to give reliable numbers in this context.