Single-axle bogies improve energy efficiency due to mass reduction. In order to estimate the mass reduction potential through KERFs, the new Copenhagen S-trains (cf. Description) may be taken as an example. They consist of 8 cars resting on 10 KERFs and have the same length as the old train sets composed of 4 cars resting on 8 conventional bogies. One KERF weighs about 50-60% of the mass of a conventional bogie (cf. Lenhard 2000). So the total mass of the KERFs along the train is about 62,5% - 75% of the bogie mass in the old trains.

Taking into account that in conventional EMUs, bogies (motor and trailer bogies) account for 30-40% of the total train weight, the weight reduction to be achieved with single-axle running gear is in the order of 7 - 14%.

The following elasticity table shows that the effect on overall energy effciency is 1-3 % in main line and high-speed transport and up to 9 % in local and regional transport.