Left Turn Arrow Operation

The following staff response was sent to a Ward 2 resident regarding left turn lanes and how they operate in Guelph:

The goal of traffic signal timing in the City of Guelph is to maximize the efficiency and safety of each intersection. Our aim is that vehicles that arrive at an intersection when the signal is red are able to clear it during the next green signal. During periods of higher traffic volumes this goal cannot always be met and motorists will experience increased delays.

Decisions about left-turn arrows are made within the context of overall intersection efficiency and safety. Although left-turn arrows may make the wait shorter for motorists turning left, they make the wait longer for everyone else. It is usually more efficient in terms of traffic management to hold a small number of left-turning vehicles than to hold a significantly larger number of vehicles that are travelling straight through the intersection.

In Guelph, there are two types of left-turn arrow indications.

1) Fully Protected Left-Turn Signal

With this type of signal, separate signal heads display a green arrow followed by an amber arrow followed by a solid red display. Right of way is provided to the driver turning left only when the green arrow is displayed.

Considerations for installation of Fully Protected Left Turn Signals include:
high left-turn traffic volume,
high opposing through traffic volume,
existing history of left-turn collisions,
sight distance for left-turn traffic is insufficient for safe completion of a left turn across opposing traffic,
high-speed opposing through traffic,
vehicles turning left must cross three or more lanes of opposing traffic, and
multiple left-turn lanes in the same direction.

Examples of this type of operation in Guelph are southbound Norfolk Street at Macdonell Street and southbound Eramosa Road at Woolwich Street.

2) Protected/Permissive Left Turn Signals

The majority of left-turn signal indications in the City of Guelph operate in this manner. Protected/permissive left-turn signals display a green left-turn arrow allowing for a protected left-turn movement, followed by a yellow left-turn arrow indicating that the protected left-turn period is ending. A green solid indication is then displayed, which allow vehicles to turn left during gaps in the opposing traffic.

Considerations for installation of protected/permissive left turn signals include:
high left-turn traffic volume,
high opposing through traffic volume,
existing history of left-turn collisions,
sight distance for left-turn traffic is sufficient for the safe completion of a left turn across opposing traffic,
lower speed opposing through traffic,
one or two opposing through lanes, and
only one left-turn lane.

Most protected/permissive left-turn signals in the City will only turn on when there is either a vehicle at the stop bar of the left-turn lane or a vehicle approximately three car lengths back from the stop bar. At locations where the third car back activates the left-turn arrow, it is assumed that at least two vehicles will safely clear in gaps of opposing traffic or during the amber display.

When the left-turn arrow is activated, motorists are given at least six seconds of green arrow time. At many locations, they are given six seconds of green arrow time, followed by three seconds of amber arrow time, and then allowed to turn left during gaps of opposing traffic. At locations where left turning vehicles cannot be adequately processed in the initial six seconds plus three second amber arrow time, additional green arrow time is provided. An example of this is the intersection of Woodlawn Road at Woolwich Street.

The performance of the City’s traffic signal system is regularly monitored which includes pro-active observations, review and updating of traffic signal timing as required at all signals in the City. In addition to this, a comprehensive operational review of each traffic signal is completed once over a three-year period and this includes conducting intersection capacity analyses and collision analyses. The result of the review determines if signal-timing changes are necessary at the intersection.  Staff