Living in Europe I’d imagine that in theory, and probably in practice, I could hit the road with a car and drive all the way to e.g. Malaysia, because the road network consists of “millions” of roads connected to each other so that I could eventually hit my destination by just driving. Other mainlands besides Afro-Eurasia have their own mainland-wide road networks which likely connect the distinct points of the continent. The same goes with islands such as New Zealand and Australia.

I’m interested in where can I find the longest road network which isn’t connected to its mainland’s primary road network (i.e. the one which is the longest of its mainland)?

To define how roads are connected, roads connected by a bridge or by unpaved road count as a connection, but e.g. ferry-connections do not count (as one can’t drive continuously from one end to other – however if the ferry takes to an island, the road network would be part of other mainland’s road network). The US’s gaps in Interstate Highways seem like a case where the roads still are connected to each other.

I have read of cities that have been built to “middle of nowhere” which could have their independent road network. Also vast mainlands with a challenging nature such as Antarctica or Greenland possibly have separate road networks which are not connected to each other nor to any other mainland. Maybe one of these could be the answer to the question.