This chapter focuses on the environmental triggers for so much of the regulation of car production. It reviews the different types of pollutants caused by cars and the development of regulation to deal with pollutants in both Europe and the United States. This review focuses on the measurement processes for pollutants and argues that the way regulators measure emissions will continue to limit the scope of the United Kingdom state’s flexibility in agreeing separate trading arrangements when leaving the European countries market. The negative externalities related to the vehicle industry and emissions are extensive. Greenhouse gases get their name from the fact that collectively they create an effect that helps trap some of the sun’s radiation to warm the planet. Externalities are ‘things’ that occur which in theory should be taken into account in the decision process. The government Brexit White Paper indicates a willingness to accede to the European testing regime for emissions.