The model structure
ASTRA consists of different modules, each related to one specific aspect such as the economy, transport demand or the vehicle fleet. The main modules cover the following aspects:
The economy module simulates the fundamental economic variables. Some of these variables (e.g. GDP) are transferred to the transport generation module, which uses the input to generate a distributed transport demand. In the transport module, demand is split by mode of transport. The traffic performance by mode is associated with the composition of the fleet (computed in the vehicle fleet module) and the emissions factors (defined in the environmental module), in order to estimate total emissions. Several feedback effects take place in the ASTRA model. For instance, the economy module provides the level of income to the fleet module, in order to estimate vehicle purchase. The economy module then receives information on the total number of purchased vehicles from the fleet module to account for this item of transport consumption and investment. Furthermore, changes in the economic system immediately feed into changes of the transport behaviour and alter origins, destinations and volumes of European transport flows.
The indicators that ASTRA can produce cover a wide range of impacts; in particular transport system operation, economic, environmental and social indicators. The environment module uses input from the transport module (in terms of vehicle-kilometres-travelled per mode and geographical context) and from the vehicle fleet module (in terms of the technical composition of vehicle fleets), in order to compute fuel consumption, greenhouse gas emissions and air pollutant emissions from transport. ASTRA also estimates the upstream emissions (well-to-tank) due to fuel production and vehicles production. Therefore, well-to-wheel emissions can be provided as well.
ASTRA is calibrated to reproduce major indicators such as transport performance, fuel consumption, CO2 emissions and GDP according to the main European reference sources such as Eurostat and the EU Reference Scenario (European Commission, 2016) for future trends. By simulating different policy bundles and framework conditions, ASTRA enables the comparison of different scenarios concerning, e.g., the diffusion of technologies, emission reductions, energy demand by energy carrier, required investments, etc.
Input and parametrization
The model includes four main components: economy, transport, technology and environment. The economy component consists of five elements: supply side, demand side (including an investment module), an input-output model based on 25 economic sectors, employment module and government module. In addition, two trade models are implemented (i.e. intra-EU trade and EU to rest-of-the-world trade).
The transport component is represented by means of two classical 4-stage transport models, one for passenger and one for freight transport, including endogenous feedback on all stages. Even if a full origin-destination matrix is not modelled, demand is segmented according to trip purpose and in different distance bands to better consider the competition between alternative modes. The transport network is not explicitly represented but information on network capacity is considered in a simplified way for the different transport modes drawing on a network based transport model such as TRUST.
The technology component covers the differentiation of road vehicle fleets into drivetrain technologies, age classes and different emission standard categories. The technologies considered are listed below and cover gasoline, diesel, compressed natural gas (CNG), liquefied natural gas (LNG), liquefied petroleum gas (LPG), battery electric vehicles (BEV), plug-in hybrid electric vehicles (PHEV), fuel cell electric vehicles (FCEV) and trolleys for urban buses and long-distance trucks.
Investments and learning curves are included in the simulation of the fleet development process. Road freight transport demand is segmented by different vehicle types: light commercial vehicles (below 3.5 tonnes), medium heavy goods vehicles (from 3.5 to 12 tonnes) and large heavy goods vehicles (from 12 to 26 tonnes, from 26 to 32 tonnes and above 36 tonnes) - according to different spatial domains (i.e. local, short, national, international). Assumptions on the composition of vehicle fleet used in each spatial domain are made to reflect the use of each vehicle type. The demand for new heavy goods vehicles as well as the replaced vehicles is associated with emission standards depending on the year of registration, covering conventional diesel technologies as well as other technologies mentioned above. Efficiency improvements are also included for non-road modes.
The environment component calculates the air pollutant emissions and energy consumption from transport based on traffic flows, the information on the composition of the vehicle fleets and on emission / energy consumption factors. ASTRA quantifies the impacts on energy consumption by fuel, CO2 emissions and air pollutants (NOx, PM, CO and VOC), as well as transport accidents and the related externality value.
Main output
ASTRA assessment capabilities cover a wide range of policies with flexible timing and variable levels of the policy implementation. Potential policies include standards setting, infrastructure pricing, fuel taxation, speed limits, carbon taxes, investment in energy and transport infrastructure, trade policies etc. A strong feature of ASTRA is the ability to simulate and test integrated policy packages and to provide indicators for the indirect effects of transport on the economic system (e.g. sectoral value-added, sectoral employment, ù GDP, trade flows, income by income groups). ASTRA has also been applied to analyse future challenges, in particular the impact of high oil prices on the EU economy and the impact of ambitious European climate policy until 2050.
ASTRA model has been successfully used for the following applications:
The indicators that ASTRA can produce cover a wide range of impacts; in particular transport system operation, economy, environmental and social indicators.
More in detail, transport system operation indicators are estimated at aggregated level (namely at Country level); nevertheless, the additional value of using system dynamics for transport modelling enriches the analysis with respect to a traditional transport model, thanks to the linkage with the modules related to economic and technological aspects. The economic module of the ASTRA model addresses the linkages between transport and economy, mainly in terms of the effects of transport policy measures on regional GDP, consumption or sectoral employment; the fleet module reflects impacts on the technology side; the environmental module deals with health impacts of air-pollution. Furthermore, these additional impacts can interact with each other. As an example, let’s take the impact of road charging. If a charge is introduced or increased for cars in the transport module, this measure has a depressing effect on car purchasing. In turn, less cars mean that some less population has a private vehicle available and, since car availability promotes personal mobility, less trips will be generated. In another step forward, the impact of road charging on the vehicle fleet propagates itself until the economic model, where less consumption and investment are modelled and therefore lower GDP, less employment and less production. The reduction of economic activity is fed back into the demand estimation, because freight transport demand depends on production and because employed people travel more than unemployed people. However, since endogenous productivity impacts are considered in the ASTRA economy model, the economic impulses of a policy may generate different impacts than in general equilibrium models primarily considering price effects.
In general, the variety of indicators estimated with the ASTRA model and the fact that these indicators are provided as time series offer the opportunity to apply a large variety of different assessment schemes to support the development of European energy, transport and climate policies. As an example, the following indicators can be provided by the ASTRA model:
