| Energy [PJ/year] | |||
|---|---|---|---|
| Fuel | Device | EndUse | |
| Coal | Boiler | Mechanical | 0.4 |
| Electricity | Electric Motor | Mechanical | 15.6 |
| Liquid fuel | Diesel Engine | Mechanical | 26.3 |
10 Train
Adapted from Cullen, Allwood, and Borgstein (2011)
Trains provide both freight and passenger transport. They are usually more efficient than road transportation, due to the “convoy effect”: the resistive forces do not increase significantly with the length of the vehicle, making long trains relatively efficient.
10.1 Characterisation
Trains must overcome resistance to motion due to aerodynamic drag, mechanical friction in the axles and wheels, and various other miscellaneous effects. Like cars, they need additional energy to accelerate the train, but this can often be recovered through regenerative braking and coasting.
Trains can be powered electrically (common for modern and high-speed lines) or by diesel-electric drive-trains.
10.2 Key issues that affect efficiency
Mechanical drag is influenced by axle loading, bearing resistance, track deflection, and the wheel/rail friction coefficient, and increases with the weight of the train.
Aerodynamic drag is determined by the train velocity, the projected frontal area and the drag coefficient.
10.3 Efficiency limits
Cullen, Allwood, and Borgstein (2011) estimated the current efficiency and possible efficiency limits for trains.
| Energy utilisation (freight) | Energy utilisation (passenger) | |
|---|---|---|
| Current | 66 kJ/t-km | 77 kJ/t-km |
| Practical limit | 25 kJ/t-km | 46 kJ/t-km |
See section S.4.5 of the Supplementary Information from Cullen, Allwood, and Borgstein (2011) for more details.
10.4 Final Energy used for trains
Trains run on multiple fuel types. This table shows the quantity of final energy \(F\) used in the UK in one year, for all trains, both freight and passenger:
According to ORR (2019), the energy use split between passenger and freight trains is approximately:
- 98% of the electricity is used for passenger trains;
- 75% of the diesel is used for passenger trains.
You will need to apply these fractions to the data in the table above (which is for all rail transport) to estimate the amount of energy use which is relevant to you.