The danger of using hydrogen gas in a vehicle may be on the same order as compressed natural gas (CNG) which is used for e.g.: some busses. Hydrogen is stored under very high pressure in tanks, which if ruptured in an accident can cause a physical explosion.

A study on CNG in busses says: "One can therefore conclude that CNG buses are more prone to fire fatality risk by 2.5 times that of diesel buses, with the bus passengers being more at risk by over two orders of magnitude."

source: https://pubmed.ncbi.nlm.nih.gov/15876211/#:~:text=One%20can%....