air
atmospheric
automobile
auxiliary
ban
car
carbon
caution
co2
dioxide
economy
emission
engine
environment
epa
exhaust
forbidden
fuel
gas
icon
idle
idling
illustration
isolated
law
no
off
parking
pollution
poster
power
prohibited
prohibition
red
reduction
road
rule
sign
signal
start
stop
symbol
system
truck
turn
unit
vehicle
warning
zone