The traffic light, also known as traffic signal, stop light,
traffic lamp, stop-and-go lights, robot or semaphore, is a signalling device
positioned at aroad intersections. It use as the road signal for directing
vehicular traffic by means of coloured lights. In most countries, the sequence
is red (stop), green (go), yellow (prepare to stop). In some cases, traffic
signals also indicate to drivers when they may make a turn.
These signals may be operated manually or by a simple timer
which allows traffic to flow on one roadway for a fixed period of time, and
then on the other roadway for another fixed period of time before repeating the
cycle. Other signals may be operated by sophisticated electronic controllers
that sense the time of day and flow of traffic to continually adjust the
sequence of operation of the signals.
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 proceeds, 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.
Traffic light system controller gives sign of direction and
warning, or it establishes a set of rule and instructions to road users to
follow to avoid any road accident. Flexible traffic light controller is needed
for maximizing the flow rate of vehicle at the junction. Development of
flexible traffic light using verilog HDL is in two mode: normal mode that
control the green light timer using switch, flex mode is using line sensor if
sensor detect car on lane green timer use the value from switch and turn to red
light if detect no car.
