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# 8 The path to fully decarbonised transport

As pointed out in Section 2.2, apart from a large dip due to COVID lockdowns in 2020 and 2021, there has been little change in UK transport CO2 emissions since 1990. This is in contrast to those from electricity generation which have fallen dramatically. Also, transport fuels are still almost totally based on oil.

The COP26 climate change meeting in Glasgow in 2021 stressed the urgent need to cut UK (and world) transport CO2 emissions and the need to cut UK oil imports has been reinforced by the war in Ukraine.

In 2021, the UK government set out a number of policy objectives for decarbonising transport (DfT, 2021a, DfT, 2021b). Ranked in terms of the ‘hierarchy of transport modes’ of Figure 7, they are:

## Improved provision for cycling and walking

There is a target that 50% of all journeys in UK towns and cities will be cycled or walked by 2030. This would include schemes to encourage schoolchildren to walk or cycle to school rather than being driven by their parents.

## A zero carbon bus fleet

This would encourage the use of battery-electric and fuel cell buses, which are already being deployed in major cities. Hydrogen fuel cells are probably the most appropriate technology for long-distance coaches.

## A decarbonised UK rail network

As shown in Figure 4, UK rail transport only makes up 1% of the UK’s domestic CO2 emissions but is the one transport mode where electricity is already a major fuel source.

In 2019, 38% of the network was electrified and this covered two thirds of passenger rail use (Lyons et al., 2021). The other third still relied on diesel haulage and rail freight was mainly diesel hauled.

The carbon intensity of UK electricity has been falling and in 2018 was only 0.21 kg CO2 per kWh. This is one reason why, as shown in Figure 6, the CO2 emissions for UK national rail were only about 40 grams per passenger-km. This was less than a quarter of that for travel in a ‘UK average car’.

Reducing emissions will require further electrification of the system. However, this may not be economic for rural lines and for freight. There are two possibilities for replacing diesel traction:

- Battery-electric trains could be used on short routes. There is nothing new about this. Between 1932 and 1949, the 20 km route from Dublin to Bray in Ireland was operated by battery-electric trains equipped with nickel-zinc batteries.
- Hydrogen fuel cell trains entered service in Germany on rural routes in 2018. Their practical range could be over 600 km. In the UK, a prototype ‘Hydroflex’ train was tested in 2020, essentially a normal suburban electric train incorporating a 100 kW fuel cell and hydrogen storage tanks. Hydrogen freight locomotives are under development, but these will each require several megawatts of fuel cell power.

## A transition to zero carbon cars and vans

According to the UK government reports, this is to be ‘market-led’. The sale of new petrol and diesel cars will only be allowed up to 2030 and that of plug-in hybrids (PHEVs) up to 2035.

There are a whole range of problems that will need to be tackled:

- Generating enough low carbon electricity to cope with the increased demand.
- Setting up a battery-charging infrastructure including provision for home charging. The UK government has a target of 300,000 public charging points by 2030 (an enormous increase on the 2021 figure of 23,000).
- Manufacturing sufficient batteries. This also includes ensuring stable supplies of key elements for both batteries and electric motors and for recycling them at the end of a car’s life.
- Producing cars with a sufficient range (and convincing sceptical customers).
- Training a workforce for the manufacture and maintenance of new technology.

## Zero carbon road freight transport

Heavy goods vehicles may travel hundreds of kilometres. They are an area where the use of hydrogen fuel cells is attractive. Battery-electric operation poses problems for recharging. One intriguing possibility is the use of catenary technology, equipping motorways with overhead wires, allowing heavy goods vehicles to recharge their batteries while still moving. Tests are underway in the USA, Germany and Sweden.

## Development of sources and distribution infrastructure for ‘green hydrogen’

This will be required for a whole range of ‘zero-carbon’ technologies.

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