I recently saw one with a 'national speed limit' (i.e. 60mph) sign, and right below it: 'not suitable for motor vehicles' (an advisory sign, so no legal weight

I recently saw one with a 'national speed limit' (i.e. 60mph) sign, and right below it: 'not suitable for motor vehicles' (an advisory sign, so no legal weight behind it). It's the default for anything considered a road, and generally unless proven otherwise the government is reasonably happy to let people use their judgement on lower-traffic areas.