More than a year ago, Volkswagen announced it was working on a project to bring its 1-Liter concept from 2002 to production reality. The three-wheeled low-slung extremely aerodynamic design still seems a bit unrealistic, but now VW is thought to be building a slightly larger, more functional city car that's shooting for the 2L/100km (117.6mpg) fuel efficiency mark.

The new '2-Liter' car is expected to be based on a shorter version of the up! (concept pictured) that will be going into production next year, reports Auto Motor & Sport. Targeting competition like the Smart ForTwo and Toyota's new iQ minicar, the 2-Liter will be a more realistic goal for production, and should come sooner than the 1-Liter, though that tandem-seated hyper-efficient vehicle could enter production as early as 2010.

VW has already hinted that a more utilitarian fuel-focused vehicle might hit the streets in the interim, though at the time in 2007, Volkswagen’s Chairman Ferdinand Piëch framed it as a 3L/100km (78.4mpg) car based around the Lupo.

Like the 1-Liter, the 2-Liter is expected to use diesel as its fuel since it's the most energy-dense of the readily available fuels in use today. A small displacement three-cylinder car, around 1L in size, will likely get the nod. Two-cylinders are in development but unlikely for use due to their high-revving nature in a vehicular application - the rougher, noisier operation doesn't result in any improvements in fuel economy.

Though it's still too early for firm numbers, power output is expected to lie in the 50hp (44kW) range, putting it squarely in the fight with its minicar companions.