How green are hybrid cars?

Hybrid vehicles tend to have lower CO2 emissions due to their improved fuel economy. Other emissions are also reduced as the engine loading is better managed than is the case in conventional petrol and diesel cars.

Climate change

Most hybrids reduce life cycle greenhouse gas emissions (such as CO2) by 15%-30% as compared to an equivalent non-hybrid model. This is principally due to the increase in fuel efficiency which results from hybridising the drive-train.

For example, the Toyota Prius achieves CO2 emissions of just 89 g/km – well below the emissions for an average conventional car (of around 140 g/km). The CO2 benefits are particularly apparent in congested driving conditions where the hybrid system is able to utilise electric drive and regenerative braking to recoup some of the energy that would otherwise be lost on start-stop driving.

Unlike other green car technologies, the future CO2 performance benefit offered by hybrids is not threatened by the improving fuel and emissions performance of conventional cars. This is because a hybridised engine will always outperform its non-hybrid equivalent. Indeed, all conventional power-trains may have to be hybridised if they are to conform to future emission standards. In other words, the future conventional and hybrid cars may be one and the same.

Local air quality

All regulated emissions are significantly reduced for a hybrid passenger cars as compared to a conventional petrol and diesel models. These include reductions in carbon monoxide (CO), nitrogen oxides (NOx) and particulates (PMs).

The lower regulated emissions are a result of the hybridised drive-train which is able to operate the main combustion engine closer to its maximum efficiency for longer than is possible in conventional cars. The effect is to lower the engine loadings, which in turn reduces time on peak power when the majority of NOx and particulates are produced.

For example, the Toyota Prius has life cycle NOx and particulate emissions over a quarter less than those for an average conventional petrol car of the same size. NOx and particulate emissions are marginally increased during the manufacturing process – however these tend to be generated well away from urban areas.

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