From innovation to penetration: Calculating the energy transition time lag for motor vehicles

To meet the targets laid down in the Paris agreement and in the European Union's climate policy documents, road vehicle fleets will have to undergo a massive energy transition in the decades ahead. New vehicles acquired need to be distinctly superior to the old vehicles scrapped, in terms of their energy efficiency and/or carbon intensity. To keep track of the process of vehicle fleet renewal and assess its time scale and potential for energy conservation and greenhouse gas mitigation, stock-flow modeling is a useful tool. The bottom-up stock-flow cohort model ensures coherence between the stock in any given year and the annual flows of scrapping, deregistration, new vehicle acquisitions, and second-hand vehicle import and export. It can be constructed from a few years' segmented data on the vehicle stocks and their annual mileage. As evidenced by our stock-flow model for Norwegian registered vehicles, it may take 5-25 years, in some cases even longer, before innovations affecting the flow of new vehicles have penetrated similarly into the stock. This energy transition time lag would tend to increase with the speed of innovation and with the target level of penetration, but decrease with the velocity of vehicle turnover.