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

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.