The government’s plans for HS2 have the potential to transform long-distance rail travel in Britain and for such a major project, it is vital that it is planned in a sustainable way. A huge range of environmental aspects are currently under study by HS2 Ltd in preparation for the environmental statement that will support the draft hybrid bill later this year, but so far there has been little consensus on one of the more strategic issues: will HS2 reduce or increase the UK’s carbon emissions?

To examine this question, Greengauge 21 was commissioned last year by the Campaign for Better Transport, Campaign to Protect Rural England (CPRE) and the Royal Society for the Protection of Birds (RSPB) to identify objectively the key factors that will determine:

  • HS2’s effect on the UK’s carbon emissions and
  • the steps that need to be taken to ensure that a consequence of HS2 is that carbon emissions are reduced.

Our research study concluded that government’s plans for high-speed rail can help meet carbon emissions targets – but there are certain conditions that must be met.

Taking the first phase of HS2 on its own, we forecast a carbon saving of 0.6 million tonnes of carbon dioxide (CO2e) over the project life. These savings could be quadrupled if government puts in place a wider package of complementary policies. And the second phase of HS2 will quadruple the carbon savings again.

As a starting point, we examined how the carbon impacts of operating transport services vary by mode of transport, taking on board the latest data on rail operations, car emissions and aircraft operating efficiency. This analysis showed that if HS2 was available for use today, the carbon emissions arising from making a trip by high-speed rail would be about a quarter of those created by making the equivalent journeys by either car or a short-haul flight.

Over time of course, the carbon efficiency of different modes of transport will change. We can expect the energy efficiency of all modes of transport to improve in response to the challenges of higher energy prices and the need to reduce carbon emissions. But the scope to achieve improvements varies across the different travel modes. High-speed rail is expected to benefit from reduced carbon emissions as electrical power generation is decarbonised, and will therefore offer a major advantage over other modes, even if, as we assumed in our analysis, the private car fleet is also switched to low-carbon fuels, with a high proportion of electric vehicles.

Carbon effects less than thought

One of the more controversial aspects of HS2 is the question of speed of operation. However, the carbon effects of operating trains at high speed are much less than commonly thought: energy use and carbon impacts do not simply increase as a square function of operating speed. Simulations carried out by Imperial College show that a London-Birmingham journey on HS2 would consume only 23 per cent more energy with a maximum speed of 360km/h (as planned for HS2) compared with a 300km/h maximum (as is the case on HS1). And higher speed means shorter more attractive journeys, attracting more people from carbon-intensive travel alternatives.

In fact, confounding many people’s expectations, high-speed rail has similar carbon emissions per passenger-km to conventional intercity rail. This is because the effects of operation at higher speed are outweighed by the benefits of carrying greater numbers of passengers at a steadier speed. High-speed trains have more than 1,000 seats per train and are typically 70 -80 per cent full. Such long trains or high loadings are not possible on today’s railway network.

To examine the overall impact of HS2 on the UK’s carbon emissions we took into account the numbers of passengers that are forecast to travel on the new services, and how this would reduce the demand for car travel, air travel and parallel rail services.

Operation of the first phase of HS2, between London and Birmingham, is estimated to reduce emissions by 1.8 million tonnes CO2e over 60 years because of the expected reductions in car and air travel. This comfortably offsets the 1.2 million tonnes of embedded carbon that will result from construction of the line.

An even more significant finding is that there is huge scope to influence the carbon outcome of HS2. Under an environmentally-responsible set of policies, the operational carbon savings could increase to 3.5 million tonnes CO2e. HS2’s carbon savings can be maximised by a mix of measures, involving both the design of HS2 itself and complementary public policies.

These public policy measures include delivering electricity decarbonisation, regulating and managing the air and road networks, and appropriate sustainable transport and spatial planning measures. Looking into the detail of the electricity generation issue as an example, the Committee on Climate Change has recommended an ambitious decarbonisation trajectory for the UK’s electricity sector which would result in the average HSR carbon emissions per passenger reducing by 92 per cent by 2050. A slower but still relatively ambitious reduction in the carbon intensity of electricity could see the total HS2 carbon savings reduced by nearly one-third. A scenario in which there is a second ‘dash for gas’ and therefore slower decarbonisation would reduce the HS2 carbon benefits by two-thirds.

When it comes to the design of HS2 itself, we concluded it was worth looking at moderating the top speed of HS2 services prior to the decarbonisation of the electricity supply, but then, in the medium term, speed up services as planned to attract passengers out of carbon-wasteful aircraft.

Franchises that unlock spin-off benefits

Also important is making full use of the capacity freed up on the existing rail network. HS2 Ltd has adopted conservative assumptions on how much of the West Coast Main Line’s capacity is freed up by HS2 for new and improved rail services. The HS2 carbon savings could be increased by eight per cent by using released WCML capacity fully for enhanced commuter or interregional passenger services. Even more benefits could be delivered with policies that ensure greater occupancy of these medium-distance trains. This highlights the value in ensuring that future rail franchises are set up so that they are able to unlock the spin-off benefits of HS2. However, the carbon savings from using three train paths per hour in each direction for freight as yet unexploited in the HS2 Ltd assumptions are considerably larger still, adding 55 per cent to the direct carbon savings from HS2. This is such a strong advantage that it would be worthwhile examining complementary measures to ensure that a major switch from HGV road haulage to railfreight is achieved as a consequence of HS2.

And finally, and even more importantly for those in the north of England who will benefit from the branches to Manchester and Leeds, the saving in carbon emissions from HS2’s operation will increase to more than seven million tonnes CO2e when the second phase of HS2 opens.