This study, co-authored by Andrew Papson of ICF International, was published by the Environmental Research Letters in November 2009. Even under highly optimistic assumptions, the compressed-air car is significantly less efficient than a battery electric vehicle and produces more greenhouse gas emissions than a conventional gas-powered car with a coal intensive power mix. However, a pneumatic–combustion hybrid is technologically feasible, inexpensive, and could eventually compete with hybrid electric vehicles. A New York Times article also highlights the results of the study.