Economical large cars for town and motorwayComparing the costs of hybrid and diesel cars

12 February 2014

Fuel bills are one of the biggest expenses that car owners face. However, cars with similar ‘combined’ fuel economy figures don't necessarily fare equally well on all roads.

If you’re looking for the most economical car, much depends on where you do most of your driving. Which? tests cars' real-world fuel economy in town driving, country (A- and B-road) driving and at motorway speeds, so you can find the cheapest for you.

Car buyers looking for a luxurious but economical large car may be considering the BMW 320d and the Lexus IS300h. While the BMW relies on a diesel engine, the hybrid Lexus is powered by a petrol engine boosted by an electric motor. The claimed fuel economy figures for these cars are pretty similar, but our tested figures show it varies drastically depending on the type of driving you do.

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BMW 3 Series saloon

BMW more economical for motorway journeys

If you spend most of your life cruising up the outside lane of the motorway, the BMW could save you nearly £700 per year over the Lexus IS 300h.

With an impressive motorway fuel economy figure of 54.3mpg in our realistic tests, the BMW 320d ED was 19.8mpg ahead of the Lexus, which returned just 34.5mpg – a figure that lags behind several petrol sports cars.

For drivers who cover 12,000 motorway miles a year, the BMW would cost around £1,375 to fuel, while the Lexus would set you back £2,045 (prices from


Lexus more economical for town driving

While the BMW may be more economical than the IS 300h on faster roads, the Lexus’s electric motor makes it extremely frugal around town. If most of your driving is at slower speeds on urban roads, the Lexus comes into its own. Its tested fuel economy figure of 97.4mpg is a whopping 38.5mpg ahead of the BMW.

Should you cover 12,000 miles in town traffic, the Lexus will only cost around £725 in petrol. Although the BMW is impressively economical for a diesel around town, you’d still be looking at a bill for around £1,270 to cover the same distance.

More economical for 50:50 town/motorway journeys

But what if you cover a mix of motorway and urban journeys? If your driving is split 50:50 between urban jaunts and motorway trips, it’s the BMW that works out slightly cheaper, costing around £1,320 for a total of 6,000 motorway miles and 6,000 urban miles. The Lexus would cost about £1,385 for the same mix of driving.

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