Mode of Control – Quick Facts
How a Traffic Signal Operates
The City of Toronto used four modes of control (MOC) at its signalized intersections – fixed time (FXT), semi-actuated pedestrian (SAP), semi-actuated vehicle/pedestrian (SAVP) and semi-actuated vehicle (SAV). FXT signals are normally installed at the intersection of two major roads or at an intersection where there is a high volume of pedestrians. A semi-actuated signal is normally installed at the intersection of a major road and a minor road or the intersection of a major road and an expressway ramp.
The City undertakes a MOC assessment for the weekday off-peak period to assist in determining the MOC required at an intersection. Four criteria are used to determine the MOC:
- the vehicle arrival rate that will cause the traffic signal to cycle constantly
- the arrival rate that requires a green time equal to the minimum pedestrian green time
- the pedestrian arrival rate at which it is desirable to display the minimum pedestrian green time with every actuation
- the pedestrian arrival rate that will cause the signal to cycle constantly
How a Fixed-Time Signal Works
At a fixed-time signal, the vehicle signal indication changes automatically from the main street to the side street even if there are no vehicles on the side street or no pedestrians wishing to cross the main street. Fixed-time signals are normally installed where two major roads intersect. Except at Audible Pedestrian Signal locations, there are no pushbuttons for pedestrians to actuate to cross the main street or the side street.
How a Semi-Actuated Signal Works
At semi-actuated signals, the signal indication will not change to the side street unless a vehicle or pedestrian has been detected. Vehicles are detected by loops (wires) embedded in the roadway at the stopbars on the side streets. The loops create an electro-magnetic field above the pavement. When a vehicle interrupts the electro-magnetic field, the signal controller knows that a vehicle is present and provides a green indication. Pedestrians show their presence by activating pushbuttons located at the corners of the intersection. If there are no vehicle or pedestrian detections, the traffic signals will remain in the main street green display for an indefinite period.
At SAP signals, a demand on either a vehicle presence loop detector or a pedestrian push button will actuate both the side street vehicle green and pedestrian “Walk” display. Vehicles and pedestrians receive the same amount of time regardless of the actuation source. While this MOC is inefficient during the overnight and daytime off-peak periods when side street vehicle traffic is light, it is seen as being pedestrian friendly because it generally reduces the wait time for pedestrians and is in line with the City’s vision of providing a better level of service to pedestrians.
At SAVP locations, demand on a vehicle presence loop detector actuates the vehicle green display; a “Don’t Walk” display will appear for pedestrians. Vehicles receive a minimum green time of seven seconds. If there is continued vehicle presence on the loop detector, this time can be extended to a predetermined maximum value. The length of the green indication can be considerably shorter than the required walk time. Independent of the demand on a presence loop detector, demand on a pedestrian push button actuates both the vehicle green display and the pedestrian “Walk” display.
At SAV locations, demand on a vehicle presence loop detector actuates the vehicle green display; a “Don’t Walk” display will appear for pedestrians. Vehicles receive a minimum green time of seven seconds. If there is continued vehicle presence on the loop detector, this time can be extended to a predetermined maximum value. There are no pedestrian crossings for pedestrians to cross the main street. This type of operation is common at ramp signals on Highway 401.
Flashing Signals at Night
The City of Toronto no longer uses flashing amber/red or flashing red/red signals during off-peak (nights and weekends) as a normal mode of operation. The use of flashing signals during off-peak periods can convey conflicting messages to drivers since Toronto motorists do not encounter this type of operation, except in the circumstances listed below. Also, at night it can be difficult for drivers to see pedestrians crossing at an intersection at which the signals are flashing. Therefore, the introduction of any flash mode as a normal mode of operation would result in a potential for driver confusion and collisions.
The use of flashing signal operation was discontinued many years ago in favour of the semi-actuated mode of signal control. At semi-actuated signals, the main street green display changes to the side street green display only if there is a vehicle on the side street detector loop or if a pedestrian presses a push button to activate the walk signal to cross the main street.
Why Main Street Countdown Sometimes Reverts to the Main Street Walk Display
This type of operation is called a “Walk Rest Modifier (WRM)” and has been in place at some semi-actuated signalized intersections for many years. At semi-actuated locations, demand on a vehicle presence loop detector on the side street actuates the side street vehicle green display and demand on a push button activates the side street “Walk” display. The WRM feature allows a main street FDW display to revert back to a main street “Walk” display if there is no side street vehicle or pedestrian demand at the end of the main street FDW. If a side street vehicle is on the detector loop at the onset of the main street amber but completes its right turn during the main street amber and/or all-red displays, then the side street green will still appear.
It is not possible to accommodate this feature at all semi-actuated signals because of signal equipment limitations.
WRMs been implemented for the following reasons:
- to make the semi-actuated signalized intersections more receptive to both side street vehicle and to pedestrians waiting to cross the main street thus reducing wait time for both vehicles and pedestrians
- to provide more responsive operation to visually challenged pedestrians at signalized intersections that are equipped with accessible pedestrian signals
Expressway Ramp Signals Without Crosswalks
The ramp signals operate in the semi-actuated (SAV) mode. At SAV locations, demand on a vehicle presence loop detector actuates the vehicle green display; a “Don’t Walk” display will appear for pedestrians. Vehicles receive a minimum green time of seven seconds. If there is continued vehicle presence on the loop detector, this time can be extended to a predetermined maximum value. There are no pedestrian crossings for pedestrians to cross the main street. This type of operation is common at ramp signals on Highway 401 since there is little likelihood of pedestrians being present at these intersections.
Flashing Red/Red Combination at Malfunctioning Intersections
City used flashing red/red at major intersections and flashing red/amber at minor signalised intersections, but it discontinued the use of flashing amber/red combination about 15 years ago since the flashing red/amber combination made it difficult for side street traffic to enter the main street and also did not provide an opportunity for pedestrians to cross the main street safely.
The City uses flashing red in all directions under the following circumstances:
- when a signal is initially activated, the signal will flash in all directions for a short period before side street green is displayed
- when there is a signal equipment malfunction
- when electricity is restored to a signal after a disruption in the electricity supply
- when the traffic control signal is placed “on flash” by the police while directing traffic
Trying to Change the Traffic Signal when Stopped at a Red Light
- Backing up and driving forward will not change your red light faster
- Flashing your headlights will not change your red light faster
- Getting out of your car and pushing the pedestrian button will not change the red light faster
Traffic Signals Changing Unnecessarily
The loops on the side street can be damaged during roadworks or by utility companies doing excavation. When this happens, the signal will serve side street even though there is no pedestrian demand to cross the main street or vehicle demand to access the main street. Loops cannot be repaired when the roadway is frozen. Therefore, loops damaged in late fall or in the winter cannot be repaired until the following spring. Even though there is wireless detection devices that can be used instead of loops, these devices are expensive and are used only in exceptional circumstances.
Stopping Unnecessarily at some Intersections along Bathurst St on Weekends
Orthodox Jews are prevented, by religious law, from operating any mechanical devices (including push buttons) at traffic control signals during the weekly Shabbat and on Jewish Holidays. To accommodate this observance, the City of Toronto provides fixed-time operation for specific semi-actuated traffic signals during these periods on Bathurst Street, Lawrence Avenue, Wilson Avenue and Bayview Avenue. Fixed-time operation is provided at intersections close to synagogues. The “cycling” of the signals permits pedestrians to cross Bathurst Street, Lawrence Avenue, Wilson Avenue and Bayview Avenue without having to activate the push button.