The current decline is ales of diesel light duty vehicle in Europe does not put EU CO₂ targets out of reach of automakers, according to a new analysis by the International Council on Clean Transportation (ICCT). Other technologies—such as efficiency improvements in gasoline engines as well as the rollout of hybrid electric power trains—offer more compelling and cost-effective pathways to reducing CO₂ emissions from European passenger cars, the ICCT says.

The share of diesel vehicles among new car registrations in the EU decreased from a peak of 55% in 2011 to 49% in 2016; recent data suggests that diesel shares continue to fall.

The ICCT projects that a decline in diesel shares down to 15% in 2025 would not interfere with meeting EU CO₂ standards and would actually decrease costs of meeting CO₂ standards.17

The ICCT notes that while diesels generally consume less fuel than comparable gasoline vehicles, CO₂emissions from diesel engines are not lower in the same proportion, for various reasons. The combustion of 1 liter of diesel fuel produces approximately 11% more energy than gasoline fuel, but the diesel fuel also releases approximately 11% more CO2 due to its higher carbon content.

On top of the higher energy density of diesel fuel, diesel engines historically possessed a number of efficiency advantages over gasoline engines. But gasoline engines are gaining ground against diesel engines thanks to a suite of efficiency technologies, such as direct injection, turbocharging and downsizing, cooled EGR, and variable valve timing. Additional advances in gasoline-vehicle design, such as variable compression-ratio engines, will further erode the efficiency advantages of diesel.

—The ICCT

The ICCT notes that coming improvements to conventional gasoline engines will narrow the CO₂/km advantage of diesel engines and, due to the lower costs of gasoline engines and aftertreatment systems, gasoline cars will be able to add additional technology to match the CO₂ /km of diesels and still cost less.

In addition, vehicle manufacturers increasingly use electric motors to complement conventional combustion engines in cars. Hybrid electric vehicles can provide efficiency gains over diesel power trains at lower CO₂ abatement costs. For instance, hybrid electric vehicles and diesel cars in the small (e.g., Renault Clio) and lower medium (e.g., VW Golf) market segments are, on average, similarly priced (±1%), but hybrid electric vehicles have approximately 20% lower CO₂ emissions. The cost advantage of hybrid electric vehicles is expected to grow as battery prices decline and diesel engines require increasingly complex exhaust aftertreatment technology. In contrast to diesel engines, hybrid electric vehicles also function as a logical stepping-stone toward fully electric power trains, which will ultimately be required to decarbonize road transportation.

—The ICCT