[Tagging] Low Emission Zones

[Dave F]

Hi

There is a boundary tag for various restrictions on motor vehicle 
entering a city:

https://wiki.openstreetmap.org/wiki/Tag:boundary=low_emission_zone

This is fine to give a general indication of its layout, but there 
appears to be no tags for nodes on the highways.

How are sat-nav routers aware of such a restriction?

Would highway=low_emission_zone work?

DaveF