The use of various signs, markings, and signals in traffic control is gradually changing due to the influence of technical advances. These advances allow coordinated operation of traffic signals over large sections of a city instead of just a single street. Traffic signs serve many purposes and have a wide variety of colours, symbols, and shapes and are among the traffic control devices that are continually being improved. Traffic signs are used to direct traffic to destinations and points of interest, to provide instructions that the road user is required to obey, and to warn of hazards that may not be evident. Pavement markings, such as lane lines and centerlines, are helpful in guiding traffic onto desired paths, especially during nighttime, and are also a very effective roadway improvement in terms of reducing crashes. Part 3 of the MUTCD (Manual on Uniform Traffic Control Devices) defines the purpose of pavement markings: "to regulate and guide traffic movements and promote safety" (Markings, http://www.transport.gov.za/library/legislation/roadtraffic/02purpose.html). Three of the most common types of road interchange are: the Cloverleaf interchange (full and partial cloverleaf), the Diamond interchange, which includes the Single Point Urban Interchange, and the three-way interchanges, which include the Trumpet interchange, the Directional T, and Semi-Directional T interchange.
One of the most well-known interchanges is the Cloverleaf interchange. Two types of cloverleaf interchanges exist: the full cloverleaf, and the partial cloverleaf interchange, also known as the "parclo", short for "partial cloverleaf". Full cloverleaf interchanges are those with loops in all four quadrants. As a result of designing for higher speed, the cloverleaf interchange will take up more land area. The classic, four-quadrant cloverleaf interchanges allow for the movement of traffic from one high capacity road to another high capacity road.
