A bollard is a pole used to close a road or path to vehicles above a certain width. Bollards can be mounted close enough to block ordinary cars, for instance, but wide enough to permit special-purpose vehicles through. The term is nautical in origin, and the American Heritage Dictionary calls the aformentioned use in landscape architecture "chiefly British", although the term has crept into the jargon of some American universities, namely Princeton.
The term "robotic bollards" has been applied to traffic barricades capable of moving themselves into position on a roadway. (See this webpage and a story from the BBC.)
