Satnav: avoid unclassified roads

Hi,

Does anyone know of a SatNav or SatNav app which has an option to avoid unclassified roads?

I know that some sat navs have an option to set the width, height and weight of your outfit but that doesn't prevent you being routed down a narrow unclassified single track lane which is a nightmare when towing a caravan.

I think the club should carry out tests on sat navs to check the routing and whether it has an option to avoid unclassified roads and if not petition the manufacturers to add this.