DfT undersells modal shift

In 2021, the Department for Transport (DfT) published transport and environmental statistics for various journeys which included Glasgow to London. However, the true carbon impact of these journeys, considering actual energy consumption, shows the DfT statistics significantly underestimate both the climate benefits of electric rail traction and the harm done by domestic aviation.

Although an inter-city electric train has only 27% the emissions of a diesel train, DfT statistics do not consider the difference the electric and diesel rail traction.

On the chart below, direct emissions are those produced by the vehicle itself and indirect emissions are those from getting fuel or electricity to the vehicle. Indirect effects are those from climate-affecting non-CO2 aircraft emissions at high altitudes.

As the trains between Glasgow and London are electric trains, an obvious issue is that DfT statistics show them to have a high proportion of direct emissions when in reality, like an electric car, they only have indirect emissions. This is because the DfT does not have a consistent approach to road and rail emission statistics. For rail it uses a national conversion factor that aggregates diesel and electric traction, whereas road vehicles are considered by the power source.

The DfT also uses generic conversion factors to estimate climate impact instead of using actual energy consumption to provide a more realistic estimate. Assessment of the carbon impact per passenger for Glasgow-to-London journeys derived in this way are shown below.

This includes the electricity consumption of a Class 390 train from an industry source. As this source is unattributable, it has been sense checked against a paper published by Professor

Roger Kemp of the University of Lancaster which quotes RSSB research showing that, in 2006, a Class 390 unit had emissions of 50g per passenger. This was on the basis of a 40% load factor compared with the 70% load factor in the above calculation. In 2006, the carbon intensity of the grid was 511g CO2/kWh compared with the 2020 figure of 193g CO2/kWh.

With adjustments for load factor and current grid carbon density, this gives current Class 390 emissions of 11g per passenger km which equates to 6.9kg for the 645 rail km between London and Glasgow. This is comparable with the estimate of 4.9kg based on the industry source, especially as this source considered that the original RSSB figure did not take full account of the benefit of regenerative braking.

The Kemp paper also shows that in 2006 a diesel HST unit had emissions of 70g CO2 per passenger km. For the same load factor, the Class 390 now has emissions of 19g CO2 per passenger km due to the significant reduction in grid carbon density since 2006. Hence, an electric inter-city train has 27% of the CO2e emissions of a diesel train.

The above calculations highlight the importance of modal shift to rail. Unless the above can be shown to be flawed, it has to be accepted that DfT’s assessment of comparative journey emissions is misleading.