That combines startling performance and low emissions, not to mention attention-grabbing and incredibly lightweight styling.
Our long-term 320 saloon may not draw the same attention on the streets as the I8, or be as lightweight, but it does share some of the supercar I8's technology.
The 3 Series Eco Pro mode reprogrammes the transmission and air conditioning system to operate more efficiently, and the dashboard display shows tips for more economical driving. In blue lettering the car shows the extra mileage achieved by the Eco Pro mode.
Among the energy saving features of the car is brake energy regeneration. Kinetic energy is released as soon as the driver applies the brake or lets the car coast. The system transforms this into electrical energy and uses it to recharge the battery. In turn, the power the engine requires to charge the battery is reduced, resulting in lower consumption and emissions.
The 320 also has electric power steering, where an electric motor replaces the more usual hydraulic system. The motor is activated when the driver moves the steering wheel.
Achieving the extra fuel economy in our car initially proved to be something of a mission - the first time I used Eco Pro mode, the normal open road mileage usage of 6 litres per 100km fell to just 5.8 litres per 100km over a long journey.
Tony Verdon and the Driven long term test BMW 320d
However, the more familiar with the car we have become, the more impressive the fuel savings have been. On one recent 174km trip we managed an average fuel consumption of 5.4 litres per 100 km. This is closer to BMW's suggested overall fuel consumption for the 320d of just 5 litres per 100 km.
Since then we have achieved economy figures of 5.3 litres per 100km, and 5.2 litres per 100km on journeys where time was not of the essence over the holiday period.
The most economical journey was a 38km round trip on crowded holiday roads where we achieved 4.6 litres per 100km.
So far, with the car having travelled about 4000km, use of the Eco Pro mode has delivered fuel savings of around 10km.
So the savings are not spectacular, and the downside to eco pro mode is a less satisfying drive.
The option is there for drivers who have the time and patience to use it but you would wonder why anyone would buy a sports edition version of the car and effectively wind-down the pleasure of driving it.