Using patents on environmental road transport technologies filed by 355 assignees over the period 1999–2010, the paper investigates under what conditions the European environmental transport policy portfolio and the intrinsic characteristics of assignees' knowledge boost worldwide green patent production. The findings suggest that post-tax fuel prices, environmental vehicle taxes, CO2 standards and European emission standards, introduced into the empirical model through an innovative methodology based on Self-Organising Maps (SOM) (Kohonen, 1990, 2001), positively influence the creation of environmental inventions. Most importantly, the paper highlights that assignees anticipate the introduction of regulatory instruments (i.e. European emission standards and CO2 targets) by filing patents before the effective implementation of regulations when legislation is announced. Furthermore, the paper provides evidence that in a technological space (which measures the applicants' technological proximity), closely located assignees enhance their patent output through the exploitation of technological knowledge produced by others. This means that the greater the proximity between assignees, the higher their likelihood of gaining advantage from this potential spillover pool. Finally, the paper observes that dynamic changes in assignees' patent portfolios spur inventive performances.