Top five hybrids with the lowest emissionsWe reveal the greenest hybrid cars on sale

16 June 2011

Small green car

Which hybrid cars are the greenest hybrids? Here are the results from our test lab

With more and more manufacturers releasing hybrid models, Which? Car has sought out the top five most eco-friendly petrol and diesel hybrids currently on sale.

Hybrid technology, where a car is powered by both an electric motor and a conventional engine, allows the vehicle to be 'greener' when running at low speeds - say in towns and cities - as this is when the electric motor takes over. 

A growing number of car manufacturers are introducing hybrid models, but are they always more efficient than an equivalent 'green' diesel? We've compared the top five with conventional-engined rivals to tell you which is best. 

Want to know more about hybrid cars? Read our guide to Green car technologies to find out more

All the makers publish claims about how good their fuel economy is and how low are their cars' emissions. But only the Which? lab tests - the most thorough consumer car tests anywhere - can reveal the truth, since we make detailed measurements of exactly how much fuel each car uses and what comes out of the tailpipe.  

Here is our list of the top five hybrids for low emissions, and how they compare with rival eco diesels on fuel consumption and emissions.

Auris hybrid generates lowest emissions

No.1 for CO2 emissions: Toyota Auris Hybrid

1) Toyota Auris 109g/km / 64.2mpg

The Auris is Toyota's medium family hatch, competing in the toughest of markets. It tops the hybrid league for CO2 emissions and fuel economy, even though our measured values (above) don't quite match the company's claims of 89g/km and 74.3mpg.

It also compares well on economy with green diesels, such as the Vauxhall Astra 1.3CDTi SRi 5dr, for which we measured emissions of 128g/km (claimed 109g/km) and consumption of 57.6mpg (claimed 68.9mpg).

Read the full Which? Car review of the Toyota Auris

2) Honda Insight 110g/km / 61.4mpg

Insight matches Prius on fuel economy

Honda Insight - clearly aimed to compete head on with the Prius

The Honda Insight is a clear attempt to take on Toyota's well established Prius. In our tests, the Insight trumped the Toyota on emissions and matched it for fuel economy. Both cars compete against a wide range of large family cars, from the Skoda Octavia to the BMW 3 Series

However, the Skoda Octavia Greenline II has far higher emissions and slightly worse fuel consumption: 125g/km and 60.1mpg. Interestingly, both cars missed their respective manufacturer CO2 claims by quite sizeable margins (Honda claims 101g/km for the Insight, and Skoda  99g/km for the Octavia.

Want to know more about the Honda Insight? Read our comprehensive review to get full details and test scores

3) Toyota Prius 112g/km / 61.4mpg

Prius powertrain has also been used in the Lexus CT 200h

Prius - optimised for economy and emissions

Toyota's Prius has long been the pace-setter for hybrid cars. It's the one everyone knows about, the one the Hollywood stars all want to be seen 'being green' in. However, when we tested it we found its measured emissions a full 20g/km short of Toyota's claim, and its fuel consumption was more than 9mpg lower than Toyota's claim.

Like the Honda Insight, the Prius competes with premium large cars like the BMW 3 Series. When we tested the it couldn't match the Prius for emissions, measuring 116g/km (compared with a claim of 109g/km). However, it beat the Prius on fuel consumption, returning an impressive 64.2mpg (claimed 68.9mpg).

Read the full Which? Car review of the Toyota Prius

4) Lexus CT 200h 112g/km / 58.9mpg

Lexus CT 200h

The Lexus CT 200h has been put through the rigorous Which? Car test

This is Lexus' first foray into the medium hatch market and the CT 200h is aims to offer buyers a stepping stone into the premium sector. However, in our tests it couldn't match the claimed 94g/km CO2 emissions figure and was a full 10mpg short of the claimed fuel consumption figure.

It still compares well against conventional rivals on emissions though. The similarly priced VW Golf 2.0 TDI GTD DSG puts out much higher emissions: 154g/km (compared with a claim of 142g/km). But the Lexus isn't quite as good on fuel economy, returning 48.7mpg compared with VW's claim of 52.3mpg.

Want to see this car in action? Watch our Lexus CT 200h video to get our initial verdict 

5) Honda Jazz Hybrid 113g/km / 60.9mpg

Jazz shares its running gear with the Honda Insight

Honda Jazz - the first hybrid supermini

The Jazz Hybrid is the first hybrid supermini to hit the UK streets. Its emissions are 9g/km more than the advertised claim, but our measured fuel economy wasn't far off the maker's claim of 62.8mpg.

However, based on CO2 emissions, it doesn't compete with close rival the VW Polo. In our tests the Polo 1.2TDI BlueMotion returned 74.3mpg and had 99g/km (compared with claims of 80.7mpg and 91g/km respectively). In addition, the Polo costs £20 less per year in vehicle excise duty and, priced at £15,480, it is more than £2,000 cheaper to buy than the Honda. 

We've just added the full test scores and review for the Honda Jazz Hybrid

What's in a few emissions?

The eco-warriors among you will realise that while CO2 is one of the biggest offenders when it comes to causing the greenhouse effect in the atmosphere (and the basis for calculating vehicle excise duty), it isn't the be all and end all. Several nasties are emitted by both petrol and diesel engines in varying proportions and we monitor these in our tests too.

The other hazardous emissions are usually found in much smaller quantities. Because many of them can be much more directly harmful to individuals than CO2, the amounts are strictly governed by the European regulations with enforcement through the Vehicle Certification Authority (VCA). We highlight any we believe are outside the legal limits.

Some of the things we monitor include carbon monoxide (CO), nitrogen oxide (NOx), nitrogen gas (N2), methane (another greenhouse gas), sulphur dioxide and carbon particulates (soot - usually filtered in modern diesel vehicles) and polycyclic aromatic hydrocarbons (PAHs) to which prolonged exposure can cause cancer.

For all these cars, our tests found very low emissions, for example with the emissions-optimised Auris and Prius engines, our testers commented that CO values were under 0.1g/km compared with many other petrol engined cars which produce up to 5g/km. And other values such as nitrogen oxides were hardly measurable.

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