My driver wouldn't stop looking at the clock on his dashboard.

I could tell he was in a hurry. But I didn't know why. So I asked him.

Mauro – my driver that afternoon in Medellín, Colombia – told me he had to be off the road in 10 minutes. Otherwise, a police officer could pull him over and ticket him.

You see, Medellín has a rule called "pico y placa" that, two days a week, forbids certain cars from being on the road between 7:00 a.m. and 8:30 a.m. and again from 5:30 p.m. to 7:00 p.m. Basically, you can only be on the road during those times if your license plate ends in a certain number.

Mauro's license plate didn't end in the right number that day. That's why he was in a race against time.

Luckily, Mauro got me to my apartment just before 5:30 p.m. But "pico y placa" went into effect after he dropped me off… So he couldn't drive home. Instead, he had to pull over and hang out in his vehicle until 7:00 p.m.

By now, you're probably wondering why Medellín has this strange rule.

It's simple.