No, not "temporary relief", as it requires modifying the engines and fuel tanks.

That means it cannot be deployed quickly, and that it's a permanent change, not a temporary thing.

not quite correct. i have had 2 vehicles here in italy that ran on lpg, and the attachment to make it work is removable, leaving no damage. lpg is pretty widely available, and you can switch to dinojuice any time.

the problems i found was the approx 30% power loss and the size of the tank, taking up half the trunk/boot, unless you get the spare tyre size tank, which doesn't give you much range, plus you have to stash the spare tire somewhere else!

upside, much less toxicity to exhaust, can enter city on pollution control days, feels a good bit greener than its liquid cousin.
downside, not permitted in underground car parks, engines not always very compatible with gas, mine needed a tweak by a 'gas expert' every so often, i'd find myself switching to petrol if i needed more pickup, if it was freezing, or if the car felt too spongy-pedaled. sometimes a couple of miles on petrol would blow whatever out the tubes and it would then run better on gas. a bit iffy all around.

some newer systems start on petrol and switch to gas.  when warmed up. it doesn't work with diesels, btw.

i though it was wonderful when i first drove with it, and reluctantly gave up on the idea.

some cars run on pure methane here too, and it's slightly cheaper than lpg.

it makes more sense too, i think, because methane is not that hard to create, with a few pigs to help...

whereas lpg...it may remain slightly cheaper than petrol, but i wouldn't bet on it being cheap for long.

imo, it's more practical in flat places, and gives ok results in a higher powered car, like an alfa, which then is hobbled down to a normal pace.

start off with a peugot or a fiat, and it becomes a lead sled.

channeling jeremy clarkson, lol!

The person who says it cannot be done should not interrupt the person doing it. Chinese Proverb.