This is one of those problems that seems like
it'd be really complicated to fix, but turns out to have a simple solution.
But then that solution turns out to be really complicated.
This is Brienz in Switzerland.
It's a small alpine village surrounded by
absolutely beautiful hills and mountains that occasionally try to kill people.
This whole hillside is slowly sliding and slipping down.
It can't hold itself up. Most of the time, it's silent and still.
But occasionally, a load of heavy rocks will tumble down.
Actually, I feel like "heavy rocks" isn't really getting the point across.
This is one of the rocks.
And worst case, it'll travel across that road
at 10 or 20 kilometres an hour, sideways.
IN SWISS GERMAN:
The village is safe from the big individual rockfalls,
it's far enough away.
The road here, not so much.
It'd be far too expensive
to build massive protection barriers all along there. And besides,
the odds of a boulder actually hitting a car are small. But not zero.
So what you want
is something that can automatically detect rockfalls and close the road.
Simple solution: a radar...
and a stoplight.
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.
Radar has the large benefit that it works in all weather
and all visibility conditions.
Radar waves can penetrate fog, rainfall, snowfall; and hence, works day at night
and in all visibility conditions, which is needed for an alarm system.
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.
Here's the complicated bit: you can't just have this stop traffic
any time the radar detects movement. Birds would set it off.
My drone would set it off.
Mischievous kids throwing pebbles would set it off. On that note...
How do you calibrate something like this?
We don't have a lot of false alarms.
It's very rare that we close the road because of something else, for example,
an approaching rain front that could look kind of similar.
Since this is such an active site, this is the perfect site
to tune your algorithms or to develop the algorithms at all.
We installed the radar in 2017,
and after a test period of about a year, it went live with the traffic lights.
And since installation, we've detected five and a half thousand events.
From an engineering perspective,
setting up a radar and a stoplight is the easy part.
The complicated part is working out the balance between false positives,
where the road is going to be closed half the time,
and false negatives, where cars could get hit by boulders.
Now I haven't seen any rockfalls here today, and I also haven't
seen the lights change.
And their logs now have thousands of rockfalls where the lights did turn red.
So I'd say: they probably got it about right.
I mean, I know it was too much to hope for, I was just hoping
there'd be just a little rock fall as I finished? Just...
just like a little one. Not doing any damage.
Just a few.
Let's do that again!
Let's do that again without worrying that a rock's going to hit me.