In that paper a class 221 is ~120g CO2 per passenger km. 222 is ~90g and a class 43 HST is about 60g per passenger km. For diesel, CO2 emissions are directly related to fuel consumption. This implies HST uses about 1/2 the fuel of a 221 per passenger km. That is something any operator should to look at carefully before taking on a 221.
CO2 emissions on a per person basis are also related to the number of seats.
It is unfair to compare a 2+7 or 2+8 HST with a 5 coach 221 and claim that a 221 uses double the fuel.
A percentage of fuel is always needed to overcome drag, the longer the train proportionally the less drag that there is as although there is more as you get longer the increases are tiny for each extra coach you add.
There's a few reasons that the 222's are better than the 221's however the main one is that they don't tilt and so are lighter.
It should also be noted that the analysis assumes that Intercity trains (which includes HST's) are loaded at 40% full whilst other trains (which includes 221's and 222's) are loaded at 30% full.
Based on that there's 214 seats used in a HST and so the total train CO2 emissions would be 128kg.
Whilst a 221 would have 75 seats used and so the total train emissions would be 90kg.
This means that by just changing the 221's to bring 40% full would change the per seat emissions to 90g and so only 50% more.
However even that's a little off, as one chart I've seen (when talking about the same fuel report) sets the HST's at ~57g Vs ~107g for the 221's. This lowers the HST results by 5% and the 222 results by 10% resulting in a direct comparison figure of:
57g for the HST fleet
80g for the 221 fleet
This is then only 40% fuel increase on a per seat basis when both units are classed as Intercity services.
Whilst that's still a concern, it's not as bad as was being made out in the above post.
