A stock-flow cohort model of the national car fleet

Abstract

Purpose Various regulatory and fiscal policy instruments are in force to reduce the amount of greenhouse gases and local pollutants emitted by private cars. The incentives operate primarily-or exclusively-on the newest generation of cars. But how fast will technological developments affecting new vehicle models penetrate into the car fleet? The speed at which the adverse effects of private car use will be mitigated through the normal vehicle renewal process, or through an accelerated one, carries considerable interest. Suitable modelling tools are needed. This paper aims to demonstrate the usefulness and flexibility of a bottom-up stock-flow modelling approach to private car fleet forecasting and policy analysis. Methods In the BIG model of the Norwegian automobile fleet, the annual stocks and flows characterising the car fleet are specified as matrices of 682 mutually exclusive and exhaustive cells, formed by cross-tabulations between 22 vehicle segments and 31 age classes. New car registrations follow from a disaggregate generic discrete choice model based on two decades of complete sales data for individual passenger car models. Results Example projections are presented onto the 2050 horizon under a low carbon fiscal policy scenario as well as a business-as-usual scenario. The fiscal policy is seen to make a large difference in terms of long term fuel consumption and CO 2 emissions. Conclusions Stock-flow cohort modelling of the automobile fleet is a powerful and handy tool for policy analysis. Even quite simple and straightforward accounting relations may provide important insights into the dynamics of fleet development. It is possible to incorporate, into the stock-flow modelling framework, interesting and useful behavioural relations, explaining aggregate automobile ownership and travel demand, scrapping and survival rates, or consumer choice in the market for new cars.

A generic discrete choice model of automobile purchase

“…At this level, the model appears to discriminate well between various policy scenarios, as demonstrated by the simulation exercise described in Section 4 above. When fed into a dynamic stockflow cohort model of the car fleet, it becomes a powerful policy support tool [15,16].…”

“…Thanks to the generic character of the model, we can predict the market shares of these hypothetical vehicles as well as the change in demand for every other passenger car in the market. Fridstrøm et al [15] show how, by integrating the discrete choice model into a dynamic stock-flow model of the car fleet, one can assess the long-term consequences of changes in vehicle technology or in the fiscal incentives.…”

Coupling Activity-Based Modeling and Life Cycle Assessment—A Proof-of-Concept Study on Cross-Border Commuting in Luxembourg

“…To estimate the share of different powertrainpowertrains and emission standards in the car fleet, a stock-flow cohort model was adopted, which can be considered a simplified version of the model presented in [46]. Given an initial age distribution of vehicles for each powertrain (and emissions standard) type i over 30 age classes j, the stock of vehicles for each age class and powertrain type (and emission standard) for year n + 1 can be derived as follows:…”

Implications of Emerging Vehicle Technologies on Rare Earth Supply and Demand in the United States

“…Our flow and stock scenarios join a growing literature of studies with long time horizons of vehicles and the materials in them [18,19,21,22,26,27]. The if-then scenario approach inherently includes assumptions and simplifications that omit various factors.…”

“…However, the growing stock of vehicles can serve as an eventual supplier of materials when the vehicles reach the end of their useful life. Research into current and future vehicle fleets and their implications on various materials has been conducted on the global scale and in the UK, Japan, and European countries [18][19][20], and some studies focused specifically on critical materials in vehicles [21][22][23][24][25][26][27]. However, to date these issues have not been explored the context of the US, currently the second largest vehicle market in the world.…”