Guarda su CINEBLOG01. The Duplex A86 is a 10 kilometer underground highway buried more than 90 meters deep. This concrete tube, measuring the equivalent of more than 30 lying Eiffel towers, is the longest tunnel in France. The result of a succession of technical prowess born from the imagination of visionary engineers, the Duplex A86 allows you to cross all of western Paris in a few minutes.