The ever-adventurous Tom Scott visited Brienz/Brinzauls, a small Swiss Alps town in the Albula Valley of Switzerland that sits between Lenzerheide and Davos amidst a falling rock zone. While the rocks pose little danger to the town, they can threaten drivers along the main road. Signs alert drivers to this danger, but in the background, rockfall is being monitored by radar. If a significant rockfall takes place, the radar activates the stoplight to respond appropriately.
So if the radar detects rockfall in a certain defined area, it triggers an alarm. The traffic lights go red, and then the radar tracks the rockfall. If the rockfall stops or it ends up in the dam, then the traffic light switches off, goes back to normal, the road is safe to pass., If the rockfall ends up somewhere close to the road, the traffic light switches to flashing orange, which means “drive carefully”, because a boulder could be on the road, or the road could be damaged.
The amount of time for the radar to detect the stoplight takes about 40 seconds.
The traffic lights are about 450 meters apart, which is the area considered as dangerous for the traffic. We’ve got about 40 seconds from detachment to a rock reaching the road, and this is just enough for the cars to escape the dangerous area. They have to drive a certain velocity, otherwise they can’t get away. And this is why cyclists are not allowed on this road.