In recent years terrorist activity has greatly increased.  Particularly popular among terrorists is the technique of loading a vehicle with explosives and driving the vehicle at high speed into a building or installation to blow it up and, and the same time, kill as many people as possible.  Attempts to thwart such terrorist activity have included the erection of concrete barriers around buildings, the use of around-the-clock sercurity personnel, etc.  The recent success of terrorists indicates that these techniques are ineffective. 
Concrete barriers are objected to because of their esthetically unpleasing character.  Most buildings that are the object of terrorist attack are designed to be pleasing to the eye and the erection of concrete barriers around such buildings destroys their esthetic character.