Left Turn Traffic Signals

Why left-turn signals?

When left-turn movements at intersections experience excessive delays, or when there is a predominance of turning movement collisions, it may be necessary to introduce separate left turn signals.

A flashing green signal or green arrow can be used to assist left-turn movements. They are not required at every intersection and should only be used after detailed studies determine their need.

Left-turn signals are used on a time-of-day basis and are usually triggered by the presence of a vehicle in the left-turn lane.

Why don’t I always get a left-turn signal?

Because left-turn signals impact the overall efficiency of an intersection, they are used only when necessary. This means that some intersections may have left-turn signals only at certain times of the day or days of the week. Weekend traffic, for example, is quite different from weekday traffic.

Left-turn signals will only turn on when there is more than one vehicle waiting to turn left. This is accomplished by embedding vehicle detection cables in the road surface to advise the traffic "controller" that a vehicle is present.

Why don’t all traffic control signals have left-turn signals?

The need for left-turn signals is dependent on a combination of factors such as vehicle volume and delay, visibility, collisions and intersection geometry.

The use of left-turn signals requires reducing the amount of green time available for all other movements. It can result in the interruption of the smooth flow of traffic and impact the overall efficiency of the intersection.

Protected/permissive left-turn signals

With this type of left-turn signal, a green arrow display is followed by an amber arrow. At the end of the amber arrow, drivers are faced with a solid green light. During the duration of the solid green light, left turns are permitted during gaps in the opposing through traffic.

Flashing green arrow

Flashing Green Arrow

The Works Department is converting to a flashing green arrow operation to improve driver perception and reaction time at all traffic control signals equipped with advance left-turn phasing. Although the Region of Durham formerly flashed its advance left-turn movements, it was prior to the regulatory change under the Highway Traffic Act which no longer recommends the flashing of the circular green ball indications in the Province of Ontario. Since 2010, all of the traffic control signals in the Region of Durham equipped with advance left-turn phasing were converted to 4-section signal displays with “solid” green arrows.

The transition to a “flashing” green arrow is an on-going effort by the Works Department to improve the safety, driver comprehension, utilization and capacity of left-turn signals, particularly for our diverse driver population some of whom have difficulty understanding advance left-turn signal phasing at larger, more complex intersections. Studies show that flashing the green arrow can increase the utilization of the advance left-turn movement by as much as 40 per cent during peak travel times.

The conversion to the flashing green arrow will be undertaken over the course of the next year with a number of intersections already in operation.

Fully protected left turns

With this type of left-turn signal, separate signal heads display a green arrow followed by an amber arrow, and then a red solid display. On the green arrow, drivers are given the right-of-way to turn left only. The amber arrow warns drivers that the left-turn signal is ending. Left-turn movements are not permitted during the through green displays.

This type of operation is used only at locations experiencing a high rate of collisions involving left-turn movements.


Traffic Control | Speed Control | Pedestrian Signals | Left Turns