There are strong overlaps and synergies among the four CPTED principles. These have been identified separately for convenience and clarity of understanding. In practice, it may be useful to see all four principles as different facets of a single technique for dealing with the security of the physical environment. In respect to the first two principles, the term ‘natural’ refers to deriving surveillance and access control results as a by-product of normal and routine use of the environment.
The fundamental premise is that criminals do not wish to be observed. Surveillance or the placing of legitimate ‘eyes on the street’ increases the perceived risk to offenders. This may also increase the actual risk to offenders if those observing are willing to act when potentially threatening situations develop. So, the primary aim of surveillance is not to keep intruders out (although it may have that effect) but rather, to keep intruders under observation.
Natural surveillance can be achieved by a number of techniques. The flow of activities can be channeled to put more people (observers) near a potential crime area. Windows, lighting and the removal of obstructions can be placed to improve sight lines from within buildings.
NATURAL ACCESS CONTROL
Natural access control relies on doors, fences, shrubs, and other physical elements to keep unauthorized persons out of a particular place if they do not have a legitimate reason for being there. In its most elementary form, access control can be achieved in individual dwellings or commercial establishments by the use of adequate locks, doors and window barriers.
However, when one moves beyond private property to public or semi-public spaces, the application of access control needs more care. Properly located entrances, exits, fencing, landscaping and lighting can subtly direct both foot and vehicular traffic in ways that decreases criminal opportunities. Access control can be as simple as locating a front office to a warehouse.
While access control is more difficult on streets and areas that are entirely open to public use, there are other techniques for controlling access in these circumstances. For example, nonphysical or ‘psychological’ barriers can be used to achieve the objective of access control. These barriers may appear in the form of signs, paving textures, nature strips or anything that announces the integrity and uniqueness of an area. The idea behind a psychological barrier is that if a target seems strange, or difficult, it may also be unattractive to potential criminals.
Because any strategy that fosters access control is also likely to impede movement, careful consideration should be given to access control strategies. Such strategies may limit the opportunity for crimes but should not hinder the mobility of potential victims.
People naturally protect a territory that they feel is their own and have a certain respect for the territory of others. Clear boundaries between public and private areas achieved by using physical elements such as fences, pavement treatment, art, signs, good maintenance and landscaping are ways to express ownership. Identifying intruders is much easier in such well-defined spaces.
Territorial reinforcement can be seen to work when a space, by its clear legibility, transparency, and directness, discourages potential offenders because of users’ familiarity with each other and the surroundings.
MAINTENANCE AND MANAGEMENT
This is related to the neighborhood’s sense of ‘Pride of Place’ and territorial reinforcement. The more dilapidated an area, the more likely it is to attract unwanted activities. The maintenance and the ‘image’ of an area can have a major impact on whether it will become targeted.
Another extension of the concept is that territorial concern, social cohesion and a general sense of security can be reinforced through the development of the identity and image of a community. This approach can improve not only the image of the population has of itself, and its domain, but also the projection of that image to others.
With clear spatial definitions such as the subdivision of space into different degrees of public/ semi-public/ private areas and the raising of standards and expectations, the level of social estrangement would decline. This is known to be related to reduction in opportunities for aberrant or criminal behavior, such as vandalism.
Maintenance and management need to be considered at the design stage, as the selection of materials and finishes will impact on the types of maintenance regimes that can be sustained over time. For example, plant material should be selected for its size at maturity to avoid blocking of sight lines.