Step on the gas

The effects of speed, part 2

In my last blog (9 May) I looked at the effects of the maximum running speed specification on track geometry. In this blog I will look at what setting a high maximum running speed specification does to fuel consumption and therefore, indirectly, carbon dioxide emissions.

The Institution of Mechanical Engineers (IMechE) has compared the energy consumption figures for trains running at different speeds (in its Transport Policy Statement 09/03, which is no longer available on the Internet). The IMechE states that a train running at 300 kph (186 mph) uses more than twice the amount of energy than a train travelling at the current maximum speed on the WCML (200 kph, 125 mph). So even if HS2 is designed for the same maximum speed as HS1 the fuel consumption is likely to be considerably higher than WCML.

Another interesting comparison is between HS2 operating at the currently planned maximum operating speed, which at 360 kph (225 mph) is less than the design maximum, and the WCML upgraded speed of 225 kph (140 mph), assuming that cab signalling is implemented.  The IMechE paper includes a graph which allows the fuel consumptions for these two operating speeds to be compared. Again the energy consumption is approximately twice at the higher speed.

This is a bit of a rough and ready calculation, but I’m sure that it makes the point; speed is not green.

The practical proof that going faster ups the energy consumption has come from China; as I reported in my blog of 5 May, the Chinese have cut the speed of their high speed services to save fuel costs.

A more detailed analysis of the effect of speed on carbon dioxide emissions was made by the consultancy Booz Allen Hamilton Ltd, or Booz and Company as they are now known. This analysis appeared in a report that, strangely, was commissioned by the Department for Transport in 2007 (available here).

Amongst other things, this report compares carbon dioxide emissions for a new high speed railway constructed between London and Manchester with the same new railway, but designed for conventional speeds. The approach taken is to consider operations over a sixty year period, with both railways carrying equal passenger kilometres. As both are new railways the carbon dioxide emissions that result from construction, also know as the “embedded carbon”, are included; however it is assumed that the embedded carbon quantity is the same for both railways.

Checkout figure 1.1a, which is on page 3 of the report and which I have reproduced below. The two left-most columns of the histogram allow the comparison between the total carbon emissions from high speed and conventional rail to be made. Using the scale on the vertical axis, I make the ratio about 1.7:1; this is quite a significant difference.

London to Manchester carbon dioxide emissions by mode (source: Booz & Co)

I think that the carbon credentials of HS2 were best summed up by Ralph Smyth, Senior Transport Campaigner at the Campaign to Protect Rural England (CPRE), who said: “It’s as if Ministers have gone out to buy a family car and come back with a Ferrari – it may impress the neighbours but it’s just not practical”.

The moral is that if you want economical fuel consumption, don’t buy a Ferrari.


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