Illumination and location of traffic signals

ILLUMINATION AND LOCATION OF TRAFFIC SIGNALS

A traffic signal is used as an instructing device that indicates the road user to act according to the displayed sign. Following the traffic signal ensures road safety and to make things simple to understand, these signals have been using a universal colour code.

• Red is generally the sign of danger or warning and on traffic lights, it signals potential hazard ahead and hence, is an indicator for the motorists to stop. 
• A flashing red light indicates the same as the stop light, which is, basically, top stop. Once you have stopped, you can proceed ahead after making sure there’s no obstacle in your path.
• A yellow traffic light is a warning signal that lets you know that the red signal is about to be displayed. Hence, when you see the yellow light, you should start slowing down to come to a stop in anticipation of red light. 
• A flashing yellow light is basically a warning signal to make the road users alert and slow down if needed.
• The green light signals safety and the word GO.
•  A traffic signal setup includes controller, traffic lights and detection. The controller works as the ‘brain’ of the entire setup and has the information that is required to make sure the lights work as per the required sequences. Traffic signals can run under a variety of different modes which can be dependent on location and time of day.
• Traffic Signal power supplies supply power to traffic signal cabinets
• The traffic signal power supply is an electrical device in the control cabinet that converts AC to correct DC voltages for various devices in the traffic signal cabinet. The nominal voltage of the power supply is 24VDC
• One of the effective options used by traffic management teams is the use of LED or light-emitting diode lamps to be able to consume less power during operations. This will also make it easier to provide backup power, such as the use of uninterruptible power supply (UPS).
• The first illuminated traffic signal was installed in London, England, in 1868.
  
• The first electric traffic signal was installed in Cleveland, Ohio, in 1914.
  
• The first signal to use the familiar green, yellow, and red lights was installed in New York City in 1918. It was operated manually from an elevated observation post in the middle of the street
  
• A modern traffic signal system consists of three basic subsystems: the signal lights in their housing, the supporting arms or poles, and the electric controller. The signal lights and housing are known as the signal light stack. 
• A single stack usually consists of three lights: a green light on the bottom to indicate the traffic may proceed, a yellow light in the middle to warn traffic to slow and prepare to stop, and a red light on the top to indicate the traffic must stop.
  
• Each light has a fresnel lens which may be surrounded or hooded by a visor to make it easier to see the light in bright sunlight. 
• A fresnel lens consists of a series of concentric angled ridges on the outer surface of the lens which bend the light to focus it in a parallel beam. 
• The light stack may have a dark-colored backing plate to make the signals more distinguishable by blocking out surrounding lights from buildings and signs.
  
• The electric controller is usually mounted in a weather-proof box on one of the corners of the intersection. 
• More elaborate traffic signals may also have electromagnetic sensors buried in the roadway to detect the flow of traffic at various points.
  
• The lens for each light is made of tinted glass or plastic.
• The bulb, known as the lamp, is designed for long life. 
• The bulb is partially. surrounded by a polished metal reflector to direct the light forward. 
• The hood or visor is made from aluminum or molded plastic.
• The supporting arms or poles are usually made of galvanized steel for strength and corrosion-resistance. They may also be made of fiberglass. 
• The controller is housed in a steel or aluminum enclosure. 
• The electrical components within the controller consist of switches, relays, and timers
• The wiring between the components is copper with a heavy neoprene rubber or plastic insulation.
• Each signal lens shall be illuminated independently and should be clearly visible from a distance of at least 400 m under normal atmospheric conditions.

Location of signals

• The Indian Road Congress (IRC) defines a road traffic signal as any power operated by which traffic is regulated, warned or directed to take some specific action.
• The primary consideration in placement of signals is visibility
• Drivers approaching a signalised intersection should be given a clear indication of their right-of-way assignment
• The lateral and vertical angles of sight towards a signal face determined by typical driver eye position, vehicle design and the vertical longitudinal and lateral position of the signal face are the critical elements to be considered while determining the location of signals
• The geometry of each intersection to be signalised along with the vertical grades and horizontal curves  should be considered in signal face placement.