Comment by ErroneousBosh

It's a pain in the arse to run vehicles on methane (CNG) because it has to be stored at around 250 bar (or, 3600psi in Old People Units), and it's really not very energy-dense so you need a lot of it.

Again though flaring it off in a gas turbine to generate electricity and heat would be ultimately less harmful than just letting it out into the air.

By contrast the tank in an LPG vehicle is at around 8 bar, not a hell of a lot more than the pressure in a truck's tyres. On my old Range Rover the LPG tank is considerably less spicy than the air suspension tank at 15 bar, which is getting into "this can injure you" territory.