What type of physical security solution should be put in place to prevent tailgating attacks on a datacenter?

Access control vestibules are designed to stop tailgating attacks, which occur when someone follows an authorized user into a space. Access badges do not prevent this, as tailgating relies on passing through a door someone with access has opened. Video surveillance may allow you to see the attack but won't stop it, and bollards are used to prevent vehicles from passing through a space.