Challenges in road transport emissions modelling at the national, regional, and local levels

Estimation of road transport emissions covering both greenhouse gases and air pollutants (e.g., NOx) have been developed at the national, regional, and local levels. Emission modelling and estimations are crucial for assessing climate change contributions and developing mitigation targets for greenhouse gases and air pollution.
Various modelling methods can be combined to estimate and project emissions at national level using a top-down approach. Bottom-up approaches can also be applied at national and regional levels for larger areas. Discrepancies between the emissions estimations at national and regional levels can provide useful knowledge to scale down or scale up emissions estimations. At the local level, (e.g., roads near schools) modelling emissions using bottom-up approaches requires traffic flow and fleet composition data which is often difficult to estimate or forecast with reliable accuracy. Similar to these data availability challenges, many context-based challenges related to modelling methods and tools occur, where emissions estimations need a different level of intervention.
The goal of this virtual special issue was to collect the latest developments around road transport emissions inventory preparation and the application of such development in emissions modelling. This special issue included both leading research and innovative techniques that are applied in different countries for emissions modelling and contains models that are state-of-the-art and state-of-practice, integration of transport and emissions models, development of emission factors, and application of emissions modelling in road transport.