There's a reason that the old, retro-futuristic dreams of monorail travel didn't come true.
Nowadays, monorails are mostly known as attractions in theme parks,
or short systems around airports,
or as impractical, expensive boondoggles.
Sydney, Australia, actually demolished theirs a few years ago.
Sure, monorails looked cool, but objectively,
they're a pretty terrible idea.
But in some places in the world: they do work.
This is Wuppertal, in Germany,
where they don't just have a monorail:
they have a century-old suspended monorail that still carries
about 80,000 people a day along miles and miles and miles of track.
Never mind your 1980s dreams of World's Fairs:
construction on this started in the 19th century,
and it's been kept up to date ever since.
It's like something out of 'Thunderbirds'.
There's a fantastic story about it once carrying an elephant --
which panicked, fell out into the river, and -- amazingly -- survived.
So why are monorails such a terrible idea?
Well, compared to other options,
they generally fail on cost and reliability.
First, you need a constantly elevated track --
the term is 'grade-separated' -- along the whole route.
Even in the rare case it's down at ground level,
you've got to put huge concrete blocks for it to run on
rather than just some rails. And given all that cost,
governments generally just build one track
so if something breaks down, the whole system fails,
and passengers have to be evacuated from a great height.
You can solve exactly the same problems as a monorail
with light rail that doesn't always need an expensive elevated track.
Or a tram, that can run along existing streets
with just some rails laid down.
Or you could just use the simplest option: a bus.
Doesn't look as cool, though.
[Translating these subtitles? Add your name here!]