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Will High Speed Rail be a positive for the UK's green agenda?

By Juan Santiago and Gary Smith

British courts have ruled that a third runway expansion of Heathrow airport would be unlawful if it failed to take the UK’s Paris climate commitments into account. Will this decision prove to be a precedent for other large infrastructure projects? Opponents to High Speed 2 (HS2), a proposed train link between London and Birmingham (initially) and to Manchester and Leeds (later) are hopeful that it will.

However unlike the Heathrow expansion which would promote the demand for carbon heavy flights, HS2 would provide passengers with the opportunity to shift to trains from cars and even (for the most northern cities) planes. According to government statistics, HS2 journeys would only emit 8g of CO2 per passenger kilometre while comparable car journeys emit 67g, and planes emit 170g. However, opponents to HS2 point out that the process of construction will also create carbon emissions, and additionally will require the removal of historic and biodiverse rich woodlands.

Any infrastructure project is a trade-off between a green cost and an opportunity to promote economic growth. Unfortunately, until all transportation is fuelled by renewable energy, the only truly green solution currently is for us to never travel to Birmingham.

In this emotional debate we note that HS2 opponents classify any newly generated demand for rail travel (ie, that is not a switch from another form of travel) as the most negative outcome in carbon terms. Such views are not compatible with government policies, and societal ambition, to generate economic prosperity in general, and promote a post-Brexit levelling up of the regions in particular.

We would argue that the green credentials of this project will ultimately hinge on how many passengers switch to the new train from cars and planes. But this is where analysis gets tricky.

The 2013 UK government estimates are much quoted, but these (by law) had to present the worst-case estimates of modal shift. These predictions are that between 1% and 4% of HS2 passengers would have travelled by air or by road respectively. These projections appear to be based on a drop in prices for both car and plane travel over time, while rail prices rise. We can’t find an alternate government sponsored “best case” estimate of modal switch.

However, we have found data from Europe where high speed rail lines have operated for many years, and these suggest that modal shifts of 30% and 15% from planes and cars respectively are possible on high speed rail routes of more than 300km. Givoni and Dobruszkes* have analysed data from France, Germany and Spain which all indicate much higher modal shifts are likely than those in the U.K. government 2013 HS2 paper. We think that the argument for comparing to the European experience is compelling.

It is also worth noting that a part of the argument in favour of HS2 is to provide much needed extra capacity, and decongest the West Coast main line which is one of the busiest inter-city routes in Europe. The existing line might then be able to carry more freight, in a shift from road haulage. This possible freight effect appears to have escaped quantified analysis.

It’s difficult to see how a project such as HS2 that results in travellers switching from air and road to rail travel could be judged in the same light as the Heathrow runway decision. The key for all nations is to reduce the size of the carbon negative consequences of every increment of economic growth, and a switch to rail travel should usually help in that respect.

However, informed choices will require more accurate and comprehensive data than that which has hitherto been available in the highly emotional HS2 debate. One key data point that is available is that £7.5 billion has already been spent on the project!

Perhaps this will be decisive?


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