hm. ok its hard to figure out where this actually gets turned on but i -think- it has something to do with the highway's complex road teleport system.
it looks like.. the road branch with this switch set to ON is a dead end, weird. im not actually sure how the hell i got this switch to turn on now. o.o
Edit: i did find out something else interesting though, the south-west highway blocked by cones leads to an area below the one im looking at, which is linked to Monochrome GB World. cool.