How should I tag a lorry escape lane?

When there is a long steep hill, there is sometimes an extra lane that shoots off the side of the road generally filled with sand or gravel. This lane (or track) is only fairly short, and it's for use only in an emergency when lorries' brakes fail (overheat generally).

How should I tag it, because I didn't see an "escape lane" tag anywhere under the roads section, or anything else?

I think it's important that these lanes are marked clearly because they are only for emergency use, one should not drive down it (or park on it) when it is not an emergency.