Where is the largest road network that shares a landmass with, but is disconnected from, a larger ('main') road network? [closed]

At first I thought this was ridiculous. How would cars get to the green area? Then I remembered the far north of Canada, my own country. Isolated villages and towns have roads with cars on them, but are not connected to the main road system. Cars come in by train or boat.

Here are Moosonee and Moose Factory:

You can see they distinctly have a road system. It is not connected to other roads in Canada and you cannot drive to Moosonee. You can drive between these in the winter on an ice road, but not in the summer.

Random facts: A factory is to a factor as a rectory is to a rector - while the word is now applied to "a place where things are made" that was not the original meaning. Moose Factory is among the oldest permanent settlements in Canada. I have been to both towns and saw no moose. Also this "far north" place is at the same latitude as London, UK, and Berlin, DE.

Juneau, Alaska would be a definite candidate. The city is at sea level and surrounded by mountains that isolate it from the mainland of North America despite being connected by land.

Due to the Darién Gap I believe the answer you're looking for is the north and south half of the Pan-American Highway. The Darién Gap is a 66 mile long break in a 19,000 mile long road system not to mention the road networks that connect to the Pan-American Highway in the north and south.

Of course this doesn't match your diagram of an island of roads encircled by a larger network of roads but it should match the rules you described.

A good candidate (if North/South America is not counted) may be the Kamchatka Peninsula in the Russian Far East. According to Open Street Map there seems to be a highway system connecting cities as far apart as Palana in the north, and Petropavlovsk-Kamchatsky and Ust-Bolsheretsky in the south (closer inspection using Bing Maps indicates that there seems to be a road connection as far south as Ozernovskiy). This would mean that the road network covers an area stretching about 900 km from north to south, and about 400 km west to east. This network is almost certainly not connected to the main Eurasian road network. The total length of the network is probably much harder to estimate. The total population in Kamchatka is around 300,000 people (although some of them may not be connected to the main road network).

The road to Cape Wrath is isolated from the rest of the Scottish road network by the Kyle of Durness - it can be crossed by driving across the beach at low tide. If that's not enough, the area is also a live missile range. It's about 14km as the crow flies from Cape Wrath to the Kyle of Durness.

If I'm understanding the rules correctly, the answer is almost certainly the road network of Japan. The entire nation of Japan has 1.2 million kilometers of roads, which makes it the nation with the sixth-largest road network in the world. While some of these roads are presumably on outlying islands (such as the Ryukyu Islands) that are disconnected from the main Japanese road network, the great majority of these roads are on the four main islands of Honshu, Hokkaido, Shikuko, and Kyushu, as well as on other small islands connected to these by bridges.

Sfantu Gheorghe in the Danube Delta covers an area a little less than 4 by 2 kilometers.
There are cars there, but you have to bring them by riverboat.

Not a winner, but still of significant distance at probably almost 600 km at times would be the

Tibbitt to Contwoyto Winter Road

A 600 km long stretch of road built each year over non permanent ice.

Whilst it is built each January from South to North (leaving no length unconnected to the main N America road system), it is likely to generally melt each spring from South to North, leaving much or most of the length unconnected.