Hydrogen engine? Not in MY car!
Gas (petrol): rather inexpensive, stable in air at room temperature, liquid at sea-level pressure (i. e. easy storage)..
Hydrogen: costs an arm and a leg, spontaneously ignite in a very wide range of oxygen concentrations (including atmosphere's 20% O2) even at low temperature (ensures cataclysmic consequences for the littlest leak), gaseous in any earth-surface conditions (i.e. a storage nightmare and delivery: requires hight-pressure tanks with regulators and NO LEAKS).
Cooking gasses like Butane or Propane are actually much safer than H2 as they will only ignite when in a well-defined mix with oxygen. H2 will ignite (read "explode", in non-controlled environments) in almost any mix with air.
You want widespread H2-powered vehicles? I say you keep your car away from my home.