Not all applications for bollards are intended to be permanent or always prevent access. As such, retractable and removable bollards have been designed to allow the owner or a potential traveler access the area normally denied by the bollard.
This is typically done in one of several ways. The lowest technology is the pipe-in-a-tube method where a socket is created in the ground. The bollard can then be removed from the socket when access is to be granted. This is inexpensive, but requires manual intervention to access the area. A second way is through the use of pivoting bollards. A locking pin is used to hold the bollard upright under normal circumstances, and removed to allow the bollard to lay flat when a vehicle is to pass over it. These bollards are generally flat in shape to allow for vehicle clearance. Often, the pin is locked in place with a padlock to prevent unauthorized access.
Finally, the most expensive method is the automatic retractable bollard. Usually hydraulic powered, the bollard actually retracts straight down into the ground and becomes flush with the surface during access. Actuation of a hydraulic bollard can be by any number of methods, from security guard push button to remote controls and toll booth pay systems.