Was it easy, though? We already knew it was a bad idea to start with, and yet it took almost a century to phase it out.

It's always been trivially easy to replace lead in car gas if you don't care about cost. There are a thousand chemicals that will increase octane levels and prevent knocking, and some of them can be bought at your local hardware store.

But none of them were as cheap as tetraethyl lead in the early 20th century, so TEL won.

(This argument doesn't apply to avgas, where TEL did/does more than just prevent knocking.)

I know that, and if monetary cost is the only thing you're measuring it's a perfectly good explanation and it's totally worth it to knowingly poison people for that.

It was introduced into auto fuel in 1921 and phased out in autos in the US from 1976 to 1996 (with the phase out being heavily front-loaded).

I would count from the very introduction, because everyone knew from the start it was a bad idea but profits spoke louder.

When do you think TEL was introduced to auto fuel?

> It was introduced into auto fuel in 1921

OK, so maybe the question then is “how many years is ‘almost a century’?”