In order to estimate the reduction of seat-specific energy consumption, single-decked and double-decked versions of an otherwise identical train (e.g. equal length etc) are compared.

Aerodynamic effect of higher car body

The cross-section of the train is increased by ~20%. Since air resistance grows with cross-sectional area in a less than proportional way, it is safe to assume that air resistance grows in the order of 10% or less.

Mass effect of higher car body

Double-decked trains are heavier than single-decked trains. The mass increment per train length is of about 10% (e.g. 11% according to a design study by Reemtsema et al. 1997).

Comfort functions

No data are available on the effect on the energy consumption of comfort functions in a double-decked train. For obvious reasons (less wall surface per seat, less interior space to be heated per seat etc), it is increased by less than the relative increase in seating capacity. 10% will be a safe upper limit here as well.

Energy consumption of the entire train

Since all components of energy consumption of a passenger train (mass, air drag and comfort energy) are increased by about 10% or less, the energy consumption will also increase by 10% or less.

Seat-specific energy demand

Since seating capacity is increased by about 20-45%, the 110% energy consumption have to be divided by 1.2 and 1.45 to get the range of seat-specific energy demand relative to a conventional car design. The result is a reduction of seat-specific energy consumption by 8% - 24%.

TGV Duplex

French TGV Duplex can be seen as a benchmark: seating capacity has been increased by 45% as compared to a single-decked train of the same length (e.g. the TVG "Réseau"). SNCF claims that this comes at virtually no increase in energy demand which means that seat-specific energy consumption is reduced by over 30%.

Fleet-wide potential

Assuming that a more than half of the regional and local lines and some of the main lines could be operated with double-decked stock in long term, there is a fleet-wide saving potential of over 5 %.