Conversion to an alternative fuel
In some LEZs, converting the vehicle to an alternative fuel (such as natural gas, liquid petroleum gas, ethanol) will allow entry into the LEZ. This is particularly the case if the conversion gives the vehicle a higher Euro standard, similar to replacing the engine
with a newer diesel or petrol engine. Gas conversions often also have to be certified and you need to provide some proof to the LEZ authorities.
Different countries have different approaches to this, in London you need to register with the Vehicle Standards Authority (VOSA), see the TfL website
. In other countries you may be able to have the change registered on your vehicle papers, or provide other proof for the LEZ authorities.
In many countries alternative fuels can be cheaper (due to reduced fuel tax), although there can be significant costs to the conversion itself. Ethanol conversions are more widely used in Sweden. Electric and hydrogen vehicles are also generally allowed in LEZs, although they are more likely to be new vehicles than converted vehicles.