Your reply is useless, but I'll rephrase to clarify anyway: how would one determine what percentage is appropriate for planning long term? I.e. so that I don't

Your reply is useless, but I'll rephrase to clarify anyway: how would one determine what percentage is appropriate for planning long term? I.e. so that I don't see potholes in 10 years, would I need 12% or 18% or 44% or <>% ? What factors would this depend on? E.g. is it always above 10% or only if the town has a very low density?