If anyone ever landed on earth they would be dissected alive and their technology stolen.
If anyone had the technology to travel the vast distances between potentially inhabitable locations in space, they would appear godlike to us. It would be like ants going to war against a herd of elephants, who happen to also be wizards.
https://en.wikipedia.org/wiki/Traffic_bollard
"Traffic bollards" or "flexible bollards" seem to be the terms for this type of bollard. They're intended to guide traffic, rather than to stop it dead as a security measure.