There were some concepts to use the Grand Central Parkway as a route, but I don't think the N train was part of that idea. I believe branches off the Queens Boulevard line or the 7 train were proposed. I guess this would really have used the Brooklyn-Queens Expressway for most of the way.
In any case, there was no serious design work done - these were just concepts. I don't know how the rail line would have fit into the highway infrastructure.
In any case, there was no serious design work done - these were just concepts. I don't know how the rail line would have fit into the highway infrastructure.