Department of State GrowthTransport

Traffic Signals

Who is responsible for the traffic signals in Tasmania?

The Department of State Growth, through its Transport Systems Group, installs, manages and maintains traffic signals in Tasmania. Note that urgent issues requiring immediate attention should be reported via phone, not email.

The Department uses the Sydney Coordinated Adaptive Traffic System (SCATS) to:

  • coordinate traffic signals
  • record faults (eg. blown traffic signal lamps)
  • record data for performance monitoring (eg. traffic volumes at intersections)
  • manage traffic incidents and special events
  • provide traveller information
  • provide parking guidance.

How do I report a traffic signals fault or issue?

Traffic signal faults can be reported by phoning the Traffic Signals Fault Line on 1300 139 933 or by emailing traffic.signals@stategrowth.tas.gov.au.

When calling the fault line to report a fault or raise a concern it will assist the operator if you can supply the following information:

  1. the location of the traffic signals    
  2. details of the fault/concern    
  3. at what time of day did you notice the fault  
  4. any other information that you consider relevant.

The Fault Phone Line is manned 24 hours a day, 365 days a year, and personnel are available at any time to make safe any hazardous situation that may arise.

Note that the email address is only monitored from 9:00 am to 5:00 pm on weekdays.

What happens when a fault occurs?

Many of the traffic signals throughout the state are connected to a central computer which registers and logs faults as they occur. Staff in the department's Transport Systems Group monitor these logs and organise the necessary repair works.

There are a number of traffic signals around the state that are not monitored by the central computer. The Department relies on information from the public to bring to its attention any faults that occur at these sites. Once informed, Department officers will attend to the fault promptly.

Why have traffic signals?

The main reason for traffic signals are:

  • to allow road users to safely navigate through an intersection
  • to give priority to a particular direction / mode of travel at different times of the day
  • through coordination, allow large volumes of traffic to pass through the network with minimal delay.    

How do traffic signals work?

A standard set of traffic signals consists of:

  • a traffic signal controller
  • vehicle detector loops and pedestrian push buttons
  • traffic signal lanterns
  • posts, pits and underground electrical cables that connect all the components together.    

The traffic signal controller

Housed in a grey metal box on a corner of the intersection, the controller is the 'brain' of the system. It is a computer that processes information received from the detector loops and pedestrian push buttons and changes the signal lanterns in accordance with its programming. Based upon the prevailing demands, the controller determines the length of the green signal for each traffic movement and controls the transition from one combination of green and red signals (known as phase) to the next. It can operate in a 'standalone' manner or be programmed to coordinate with a series of adjacent traffic signals.

Vehicle loop detectors and pedestrian push buttons

Vehicle loop detectors and pedestrian push buttons are the 'eyes' of the system. They are mechanisms motorists and pedestrians use to make the controllers 'see' them and change the signal to give them right of way.

Vehicle loop detectors are loops of wire buried in the road leading up to the stop line at the intersection. When a vehicle is passing over the loop the magnetic field (inductance) of the loop changes. The controller detects that a vehicle is waiting to proceed through the intersection.

Likewise, when the pedestrian push button is pressed the controller knows that a pedestrian is waiting to cross.

Traffic signal lanterns

Traffic signal lanterns are the means by which the controller directs traffic. They tell the road users when to go and when to stop. Tasmanian traffic signal lanterns follow universal traffic signal colour conventions. GREEN = Go if it is safe to do so; YELLOW = Stop if it is safe to do so; and RED = Stop.

The Department has converted 70% of standard signal lanterns to ELV/LED (Extra Low Voltage/Light Emitting Diode) lanterns which are very energy efficient and long lasting.

Signal phases and cycles 

Each combination of green and red signals that the controller is programmed to display is called a phase. Each phase has a programmed minimum time so that once the signals have entered a phase they cannot change again until the minimum time has expired. One complete sequence of all the vehicle and pedestrian movements (phases) at an intersection is known as the signal cycle. The cycle time varies by location and time of day.

The yellow signal

Traffic signals change from green to yellow to warn approaching motorists that the signal is about to turn red. The length of the yellow signal depends on the speed limit of the road. The yellow signal means stop if it is safe to do so. Any vehicle travelling at the speed limit toward a green signal that changes to yellow should have sufficient time to stop safely or clear the intersection before the signal changes to red if the driver has entered the intersection.

All-red time

The all-red time is the time between the end of the yellow signal on one phase and the commencement of the green signal on the next phase. All-red time is used to provide a safe clearance for vehicles that cross the stop line towards the end of the yellow signal as they may be in danger of colliding with vehicles or pedestrians starting in the following phase.

The all-red time is based upon the physical size of the intersections and speed limit of the road. Similar to the length of the yellow signal, the all-red time does not change throughout the day.

What are the rules about how a pedestrian uses pedestrian lights at traffic signals?

Click here for information about using pedestrian lights at traffic signals.

Modes of operation for traffic signals

The traffic signals at each intersection can be programmed to operate in an isolated mode or be coordinated with traffic signals at adjacent intersections to allow the progression of traffic along the road.

In isolated mode, traffic signals changes are driven by the vehicle loop detectors and pedestrian push buttons at the intersection (see above). Isolated mode works very well for intersections with low volumes of traffic, no major flow of traffic in one direction or intersections that are a long way from each other.

The other mode is 'coordinated'. For traffic signals to be coordinated they need two things:

  1. A common signal cycle time: The signal time is the time it takes to run through one complete sequence of all the vehicle and pedestrian movements (phases) at an intersection.
  2. A timing offset between the start of one intersection's main green movement and the next intersections main green movement so that vehicles travelling at the designated speed limit leave the first intersection on the green signal and reach the second intersection at the same time as its signal turns green.    

The benefit of coordinating signals is that large volumes of traffic can pass through multiple signals with minimum delay.

The disadvantage is that because the common cycle time is set to meet the needs of the largest and most complex intersection in a series, signals at smaller intersections in the series can appear to change too slowly.

When coordinating traffic signals, the Department works hard to strike a balance between allowing the progress of vehicles along the main road and keeping the wait times for side street vehicles to a minimum.

How does traffic signals coordination work?

The following link on the Queensland Department of Transport and Main Roads website explains how signals can be coordinated. It also provides an insight into the complexities and challenges in coordinating signals, especially across a number of intersections.

http://www.tmr.qld.gov.au/Travel-and-transport/Road-and-traffic-info/Traffic-Signals-Information#Coordination

Who is responsible for electronic school speed signs?

The Department’s Transport Systems Group is also responsible for the control and maintenance of electronic school speed signs. However, the operating times for each school zone are nominated by the relevant school to reflect the peak periods of activity.

Contact Us

If you need further information on traffic signals please contact info@stategrowth.tas.gov.au.

Attribution Statement: The content in this FAQ has been adapted from the Traffic Signals Information page on the website of the Queensland Department of Transport and Main Roads. The original content is available at http://www.tmr.qld.gov.au/Travel-and-transport/Road-and-traffic-info/Traffic-Signals-Information.  Licensed  under Creative Commons Attribution 3.0 Australia.