This paper aims to develop a testing and scoring mechanism, to assess the buyers’ behaviours on purchasing green vehicles. As there are various vehicle types with different emission properties presented in the current market, a Key Green Performance Indicator (KGPI) framework is designed to choose vehicles by comparing all the relevant factors affecting consumer choice on green vehicles, including different emission damages, buyer cost, car performance, and other incentives. The novelty of this paper is to combine all the factors to produce a unique single score to present vehicle cleanliness and guide buyer choices. The findings will provide useful information to guide buyers towards the cleanest available vehicles and promote the manufacturing of new cleaner vehicles to the market. © 2020 Elsevier Ltd