Diesels more efficient than hybrids on the open road

Lexus CT200h
Hybrid Lexus CT200h - Credit: Lexus

If you've been tempted by the idea of making the switch to a hybrid car in an attempt to reduce your motoring costs, you may want to consider how and where you use your car, as diesel vehicles are more efficient away from congested city centres, a new report states.

A study conducted by Emissions Analytics found that while hybrid cars excel in urban start-stop traffic, where limited low speed progress can be made on the battery alone, they were far less fuel efficient at higher speeds, such as when cruising on motorways.

This is largely because hybrid models rely on recharging their batteries by capturing energy from braking – something that happens less often in out-of-town driving.

Manufacturers often focus their attention on making a hybrid's batteries as efficient as possible, meaning that the engines used are often not as highly developed. Most hybrid models also use petrol motors rather than more efficient diesel units.

Diesel cars excel under motorway conditions, though owners can often find they are less efficient in urban driving.

However, as official economy and emissions testing occurs at very low speeds, there are concerns that drivers may be buying hybrids under the misguided expectation that they will be the most fuel efficient option in any given situation.

Nick Molden, spokesman for Emissions Analytics, said: "We are not saying hybrids are great or they are terrible – they have a particular role to play and for that they are good, but if you put it to the wrong use you can find it is worse than having a frugal diesel engine," The Telegraph reports.

"To some extent the hybrids have had the aura that they are unquestionably a good thing, the general feel out there is that if you have a hybrid you are doing something that is unquestionably good for the planet and that's not necessarily true, and it's not necessarily good for your wallet."

The company's study consisted of performing real-world driving tests on two hybrid models and eight standard diesels. All had engines between 1.5 and 2.2 litres in size, power up to 150bhp, and all were standard two-wheel drive vehicles.

It found that the better performing of the two hybrids, a Toyota Auris, returned 58.7mpg on average, but was bested by standard diesel versions of the Honda Civic, Skoda Octavia, Peugeot 308 and Mazda 3.

Efficiency for both types of vehicle dropped in stop-start driving, though only marginally in the hybrid models, compared to around six per cent for diesels.

However, at motorway speeds, the fuel efficiency of conventional cars rose by between 18 to 27 per cent, whereas hybrid models showed a 1-8 per cent improvement.

"Hybrids may deliver good but not best-in-class fuel economy, but they are typically the cleanest, and if you are a light-footed, congested-town driver, they are ideal," Mr Molden continued.

"But if you are a motorway cruiser, you are working mostly on the engine and running on a relatively inefficient petrol engine. It is about matching the vehicle to the job."