A new study has found that the diesel share of the German car market has peaked and that it will start falling from around 48% today to 30% by 2020.

The study by the Centre Automotive Research (CAR) at the college of Gelsenkirchen, and headed by Ferdinand Dudenhöffer, cites seven reasons for the future fall in diesel share which it says will be damaging to the competitiveness of the German automotive industry, which is a world leader in diesel technology.

The study, reported by Automobilwoche, said the main reason for the end of the diesel boom is the improved efficiency of petrol cars, downsizing, second generation technology and double turbocharging. In addition the price differential between diesel and petrol is falling.

The third reason is falling values of used diesel cars. CAR attributes this partly to the fact that private used car buyers generally drive fewer kilometres than new car owners and this, combined with the reduced price advantage, means that diesel no longer adds up as an alternative.

Company car buyers are also turning away from diesels, partly because price rises for diesel cars have been higher recently, as new technology such as Bluetec (Mercedes) and BlueMotion (VW group) has been added to newly-launched models.

From 2010 all diesel cars will be required to have NOx filters, which will add further cost. These filters will require servicing, too, leading to even more cost for owners.

Petrol hybrids will put the final nail in the coffin for diesels. Hybrid technology will be enough to give petrol a firm CO2 emissions advantage over diesel.

For 2015 CAR is forecasting a 38% share in diesel, falling to 30% by 2020.