separately identified here because of data unavailability or unreliability.1 In this analysis, commuter rail is included in the figures for conventional rail services. This is a significant limitation for some aspects of the analysis, since commuter rail is an important part of urban mobility, but unfortunately it cannot be fully isolated.

Classification issues are simpler for freight rail, which is defined here as the transport of goods Page | 22 on dedicated freight trains.

Key parameters

The extent to which rail services are used is defined here as rail activity. It is expressed by measuring the number of passengers or tonnes carried across a given distance, in passengerkilometres or tonne-kilometres (ten individuals riding a train for ten kilometres equates to 100 passenger-kilometres, and likewise for tonnes of goods). These passengers or goods are transported on trains driven on rail networks across a given distance. Train activity, measured here in train-kilometres, is defined as the sum of all kilometres driven by all trains in a given year.

The extent of the networks catering for these movements is expressed in terms of track-kilometres, which may be aggregated into a lower number of line-kilometres, reflecting the fact that lines can be composed of one or more tracks.

Trains are assessed in terms of their energy consumption (typically expressed in units of energy per train-kilometre) and their greenhouse gas (GHG) emissions. The latter are measured here either as well-to-wheel CO2 emissions (i.e. emissions imputable to both the production of the fuel and its use) or as life-cycle CO2 emissions, also accounting for the CO2 emissions resulting from the construction of trains and rail networks.

Data sources

Historical data for conventional and high-speed rail transport data come from the International Union of Railways (UIC, 2018), up to 2016. To supplement these data, the figures are processed by the International Energy Agency (IEA) and combined with statistics from national sources2 and the IEA energy balances. For urban rail, historical data are derived from the International Association of Public Transport (UITP) global databases for metro and light rail statistics, the Millennium Cities Databases (UITP, 2015; UITP, 2017; UITP, 2018b), and the Institute of Transportation and Development Policy’s rapid transit database (ITDP, 2018).

Historical data for all modes other than rail are collected by the IEA as part of the activities related to the development of the IEA Mobility Model (IEA, 2018), which is a techno-economic database and simulation model that enables detailed analysis and projections of transport activity, vehicle activity, energy demand and well-to-wheel greenhouse has gas and pollutant emissions. Historical data are available to 2016. The IEA Mobility Model was used to develop estimations for 2017. The same model is also the main tool used for the development of the quantitative projections analysed in this report (IEA, 2018).

References

AAR (Association of American Railroads) (2017), AAR Analysis of Class 1 Railroads, retrieved

–(2017), Light Rail Transit World Statistics Database, UITP, retrieved 26 July 2017.

–(2015), Millennium Cities Databases for Sustainable Transport, UITP, retrieved 22 March 2016.

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