New BMW 320d EfficientDynamics: Most Fuel Efficient BMW Returns 57.4mpg - 4.1 lt / 100km

Just to get an idea of how low these figures are, in the EU test cycle, Honda's dedicated mild-hybrid, the smaller-sized Insight, is rated at 4.4 lt petrol/100km (53.5mpg US or 64.2mpg UK) with CO2 emissions of 101g/km.

The 320d EfficientDynamics is powered by a 2.0-liter four-cylinder diesel engine with a single turbocharger that develops 163 HP between 3,500rpm to 4,200rpm and 360Nm or 266 lb-ft of torque from 1,750rpm to 3,000rpm.

The sprint from zero to 100 km/h (62mph) comes in 8.2 seconds while acceleration in fifth gear from 80km/h to 120km/h (50mph to 75mph) takes 9.6 seconds. The saloon can reach a top speed of 220 km/h or 137mph.

Changes over the standard 320d include improvements to the engine construction, a longer rear axle transmission ratio, lowered suspension and the use of specially designed aerodynamic alloy wheels with Michelin EnergySaver tyres.

The car also comes with a dual mass flywheel with springs between the two parts to help smooth out any engine vibration through the drivetrain as well as new centrifugal pendulum absorbers to further improve smoothness.

Like other BMW models, the 'green' 320d comes fitted with the existing suite of BMW EfficientDynamics technologies such as Auto Start Stop, Brake Energy Regeneration and Electric Power Steering as standard.

According to BMW, despite the numerous upgrades, the new 320d EfficientDynamics Edition model will come at the same price as the "regular" 320d, which is still included in the model range. Sales are expected to begin towards the end of the year.