[Jonny5]

Adelaide has been changed to have gigantic left hand turn lane queue space and it's rarely used or needed. Cars that could go through and not block streetcars now sit in front of them. Terrible design.

 

[ZEBuilder]

In Mississauga I don't think I've ever seen a left turn signal activate without a vehicle present. Although I have seen them not activate when there was just one or two vehicles in the left turn lane (some left turn lanes in Mississauga are quite lengthy).

The reason they don't activate when there's only one or two vehicles is due to the implementation of setback loops, these are often set back 15-20m from the stop bar such that the LT lane only triggers when the queue is at minimum that long. There is no sense in delaying a road like Mavis if there is only 1 car needing to turn left.

Other intersections are operated using overhead detection, they typically trigger whenever a vehicle is in the detection zone, however they can again be manipulated to act in a similar nature to
set back loops where a certain portion of the field needs to be filled before the LT signal triggers.

 

[reaperexpress]

Or so lightly used? Like for example a left hand turn signal that is on for 2 seconds before turning yellow, and meanwhile there is a queue of 40 cars waiting to turn.

Is there any coherent strategy city wide for left hand turn signals? Or are these basically set ad-hoc and forgotten about.

According to the City of Toronto Traffic Signals Operating Policies, the minimum duration for any green is 6 seconds for a turning phase, or less than 7 seconds for a thru phase. There is absolutely no way you saw a 2-second green light. If any interval violates a requirement (e.g. less than the minimum green), the conflict monitor will immediately shut the intersection down (flashing red in all directions).

Protected-permissive left turn phases with a dedicated lane are typically called & extended by a dector located three cars back from the stop line. If there are only 1 or 2 cars waiting it's not worth making others wait through the 10s left turn phase (6s green, 3s amber, 1s gap). If there are more than 2 cars, the left turn green arrow will stay green as long as cars continue passing over the detector, or until the maximum green time. In Toronto, there is a high priority on pedestrian delay, so the maximum green time for left turn phases is generally kept as short as possible, since longer maximum green times will increase the cycle length and increase the pedestrian delay. Left turn phases are generally the least efficient use of an intersection's time, since you'll only get about 1 car per second (1.1 people per second) through the intersection (a car every 2 seconds in each direction). A thru phase with pedestrians, bikes and transit will carry vastly more people in that time.

Some signals only have left turn phases callable during certain busy periods. During lighter traffic periods, even if there are 3 cars in the lane the left turn signal will not be called. This enables the cycle length to be reduced since the cycle length doesn't need to account for the length of the left turn phase, which reduces pedestrian delay.

Toronto Signals Operations Policy 5.4.1:

Whenever I drive in the US I rarely if ever see a left hand cycle unexercised or under exercised.

Sorry for the old man rant

In the US they typically don't care about pedestrian delay, so they'll happily run cycles as long as 160 seconds. Toronto generally caps its cycles at 120 s, though there are some large intersections where higher cycle lengths are unavoidable.

 

[micheal_can]

This was on CBC's The National.