The three-year HyTunnel CS project culminated in the report titled Deliverable D6.9, “Recommendations for inherently safer use of hydrogen vehicles in underground traffic systems.” The HyTunnel CS project aimed to perform pre-normative research for the safety of hydrogen-fueled vehicles traveling through tunnels or entering confined spaces. The main objective was to compare the relative risk of hydrogen vehicles entering underground traffic systems to existing fossil fuel-powered vehicles [1].