Tiny, economical, yet stylish and trendy, the Smart ForTwo has proved a mammoth success in the U.S., with actual demand far outstripping projections. Toyota's iQ, Audi's A1 and BMW's upcoming Project 'i' minicar are both on the table for U.S. sale as well - though none are confirmed yet - so Smart is already preparing to improve upon the ForTwo with a new four-door four-seater called the ForTwo +2.

The somewhat awkward name is a result of wanting to distance the new car from the ForFour, Smart's previous - and rather unsuccessful - four-seater offering (pictured). The return of a four-door Smart has been in the works for over a year, though the new car isn't expected to share anything with the original.

Smart's ForFour was based on a shared platform with Mitsubishi, which the Japanese carmaker also used for its Colt. The new ForTwo is expected to grow on a modified version of the ForTwo's platform, however, sharing the rear-engine, rear-drive layout of the minicar.

Development work on the new car is still in the early stages - a production version isn't expected until 2012, says AutoExpress, though we'd expect a concept version of the car to make its debut later this year or sometime in 2010 to help hone demand to a razor's edge.