The road from Vaduz to Malbun passes through the Gnalp-Steg tunnel, which itself is a bypass of the original road that led over the mountains via Sücka, including a very short tunnel of its own. The tunnel is wide enough for two fairly narrow lanes, but its roof is semicircular, meaning that buses and lorries have to use the middle of the road. To prevent mishaps, there are traffic lights at either end whose default state is flashing amber at both ends, but which react when you approach them in a large vehicle. I only travelled the road in the bus (several times over three days) and every time the bus approached either entry the flashing amber changed to solid amber and then red, giving green when any traffic already in the tunnel had cleared.
I've not encountered this kind of dynamic traffic light before, which not only detects an approaching vehicle (there are plenty of those), but also determines its action based on the size of said vehicle. It must also detect vehicles coming in the other direction, even if they're small enough not to trigger the one-way feature, because sometimes it cycled quickly from flashing amber - amber - red - green, and other times there was a delay for oncoming vehicles. I wonder how reliable it is at detecting that a cyclist has entered the tunnel but not left before letting the bus through?
