Is it normal to have sex in public?

I'm 19 and very sexually active, maybe a bit TOO sexually active, to be fair.

I don't have a steady girlfriend but have a few girls who I meet up with, sometimes I go to their place and sometimes they come to mine, but recently we've been trying some new things.

We usually wait until it's dark outside and go to a park, we've done it on the climbing frames, over benches and once on the slide.

The reason I think it's getting out of hand is because the last time we did it, it was on a bus. It wasn't packed, but there was someone near the front and I'm pretty sure they heard us hard at it.

Is this normal?