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use relative energy savings in % per 10 % weight reduction for the rail vehicles and ap- ply these relative energy savings to a representative train relation for exemplification.

To determine the actual specific savings, either measured data from tests or simu- lated data obtained from complex models can be used. To date, most energy savings by weight reduction have been calculated by a regression line from the weight of differ- ent vehicles. This method seems to be unsuitable for a precise determination of energy savings, because differences between the vehicles (technical variations, dimensions, etc.), which are relevant for the energy consumption, are not considered [EBERLE & FRANZE 1998]. This method should therefore only be used if no simulation or meas- urement results are available. For some vehicles a range of estimates on weight in- duced energy savings can be found in the relevant literature. These estimates lack a scientific chargeable basis, but will be used for comparison or if no tests or simulations are available.

The life-time performance is of great influence on the life-time energy savings. Specific energy savings are of great importance only with a life-time performance in the same order of magnitude. For the life-time performance, the whole life of the vehicle has to be considered. Even if a vehicle starts its “career” as a commercial vehicle in the U.S. and continues to operate for several years in rural Mexico as a taxi, the weight reduced option will continue to save energy without any further maintenance. No definite statis- tics for the global average of the entire life-time performance exist. Estimates are based on national statistics, communication with experts from associations and operators as well as analyses of used vehicle trade markets.

The total energy consumption and savings of a vehicle are also determined by the effi- ciency of the transmission, engine and energy supply. These efficiencies vary for the different vehicles, mainly depending on the energy carrier used. To allow for a com- parison of the results we will determine the primary energy savings, which take into ac- count the structure of the energy supply (e. g. the energy split for electricity production), as well as CO2 emissions which take into account the carbon intensity of the fuel pro- duction. Therefore, we include the production and distribution of the energy carriers in our system boundaries.

The data used in this study are from a variety of sources and are of different qualities. The main focus is on North America and Europe due to availability of data and the im- portance and number of transport vehicles in these countries. Data have been gathered mainly by literature research (scientific publications and published documents from political and industrial organisations) and communication with associations, industry and research institutes. Data on

  • the specific weight induced energy savings per 100 kg or 10 % weight reduction


  • the life-time performance

have been gathered, documented and analysed. Data gaps have been filled by using expert judgements, data extrapolation or system modelling. The data quality, however, is very different, depending on the vehicles as well as the parameters. The appraisal of the potential life-time energy savings is undertaken on the basis of this unequal data.

Data uncertainties arise from a number of sources. For the specific energy savings

Energy savings by light-weighting

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