Interestingly, they first used movable concrete barriers in the late 1940s, in California. The plastic ones came out in the late 60s. Some of them contain sand or concrete.

Err...

I modeled traffic. I spent as much time as I could being on-site for data collection. I've also spent way too much mental energy on learning about roads. This is because I am still largely a child, even though I'm old.