Intelligent Transport System (ITS) strategies can significantly reduce CO2 emissions of vehicles. Since the impact of ITS measures is highly dependent on driver acceptance and compliance rates, it is important to study the response of human drivers to new ITS strategies (the human factor). However, there is currently no low-cost yet effective method to investigate the human factor. Conventional driving simulators offer high realism of the driving and traffic environment, but they are expensive, not easily accessible, and restricted to one driver at a time, and hence make it difficult to conduct large-scale behavioral studies. Web-based survey methods are accessible but they do not allow to capture a person's moment-by-moment driving behavior. Therefore, we propose OpenEnergySim, an online multi-user three-dimensional (3D) simulation space based on emerging 3D Internet technology. OpenEnergySim can provide three functions in a realistic and integrated environment: (1) driving simulation of multiple users (as graphical avatars) in a simulated traffic network by using computer keyboard or game wheel; (2) visualization of the result of microscopic traffic simulation and (metaphoric) visualization of CO2 emissions; (3) a shared real-time collaboration space for testing and comparing the effects of green ITS strategies on CO2 emission reduction. Those features make OpenEnergySim a highly accessible platform for conducting behavioral studies in the transport domain. Since driving simulators have to address behavioral validity concerns, we will present results of a study where car following behavior in the virtual world is compared to both real-world data and Gipps' car-following model. © 2011 IEEE.