◄Previous: 5.2 Technologies and standards

# 5.3 Reducing CO2 emissions

For petrol and diesel cars, CO2 emissions are directly related to the fuel economy of the vehicle.

Key technologies for improving fuel economy include:

- optimisation of the internal combustion engine (ICE) for enhanced fuel efficiency using computer engine management
- auto start/stop – the automatic switching-off of the car’s engine when it idles (e.g. waiting in queues or at traffic lights). This can improve fuel consumption by up to 10% in urban driving.
- tyres with a low rolling resistance
- driver information technologies – for example, continuous displays of fuel consumption and indicator lights advising drivers when to shift to a high or lower gear to get the best fuel efficiency
- improved aerodynamics. This can include body streamlining, radiator grilles, underbody panels and spoilers designed to reduce drag.

Cars featuring these technologies may be sold as ‘eco’ models.

The most significant new technology has been the move to hybrid petrol-electric and diesel-electric drive trains, incorporating an electric storage battery. This allows:

- the use of regenerative braking to recharge the battery when braking or decending hills. This cuts the need for the internal combustion engine to generate electric power.
- tightly controlling the ICE engine to only run at its peak efficiency and minimum pollution levels.

This can be considered as part of the switch towards full battery-electric vehicles and will be described further in Section 7.

The tightening standards meant that the average CO2 emissions of newly registered cars in Great Britain fell from about 170 grams per km in 2005 to only 122 grams per km in 2015, (DfT, 2015).

Although this was a significant improvement, it had become obvious that mere incremental changes to the existing fossil fuel-based technology would not produce the large reductions in national CO2 emissions required to meet a policy of Net Zero emissions by 2050. In 2020, the UK government announced that the sale of new cars and vans powered solely by petrol or diesel fuel would be phased out by 2030.

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