Hydrogen-based mobility is in its infancy, yet it is foreseen as playing a substantial role in the future transportation system of Europe, including in Luxembourg. ENGIE, a leader of the energy sector in France, is contributing to the deployment of fuel cell vehicles, by accompanying willing individuals and companies on a path towards more sustainable mobility modes. A pilot project with this exact objective, SPHYNX, is already ongoing in the Paris area. A rapid deployment of an emerging technology carries along profound infrastructural changes, together with their inherent environmental consequences. Due diligence is therefore needed to make the right choices for a territory in terms of hydrogen-based mobility. Particularly, both policymaking and individual behaviours will influence the course of these changes.Based on a tight collaboration between ENGIE and LIST, HERMES will provide an appropriate decision-making tool for territories to assess their mobility policies. Such a tool will combine state-of-the-art simulation and environmental impact assessment methods to offer a precise overview of the medium-term consequences of policy choices. Combining ABM-LCA methods, whose policy-relevance has been proven, with real-world data from the SPHYNX pilot project will give unprecedented insight in terms of public acceptance and decision criteria that lead to the rapid deployment of fuel cell vehicles. Results from various policy scenarios will help identifying the most efficient policy levers to trigger fuel cell vehicle sales, both for captive fleets (taxis, company cars, and urban freight distribution, which are now the focus of the SPHYNX project) and private vehicles.