  Operational urban transport models require to gather heterogeneous sets of
data and often integrate different sub-models. Their systematic validation and
reproducible application therefore remains problematic. We propose in this
contribution to build transport models from the bottom-up using scientific
workflow systems with open-source components and data. These open models are
aimed in particular at estimating congestion of public transport in all UK
urban areas. This allows us building health indicators related to public
transport density in the context of the COVID-19 crisis, and testing related
policies.
