[Tagging] Access restriction for gas-powered vehicles

[Michal Fabík]

Hi,
I'm sure this has been asked before, but I can't seem to find anything 
on the topic in the Wiki. How do you tag access restriction for 
LPG/CNG-powered cars, as is sometimes the case in underground garages.
I'm thinking of something to the effect of:

motor_vehicle:conditional=no @ (fuel=lpg;cng)

But I'm pretty sure this is wrong, because AFAIK the engine doesn't 
understand the connection between motor_vehicle and fuel.

Any ideas?

-- 
Michal Fabík