reaperexpress
Senior Member
In Ontario, there is a delay of about 3± seconds, when the traffic signals turn red in one direction before the other direction turns green (or the left turn phase). During that delay, the other direction transit vehicles should be given their priority. At the end of those 3± seconds, the transit signal should end and the other direction turns green (or the left turn phase begins). If the transit vehicle is still in the intersection, the left turn vehicles can still edge into the intersection and wait for the transit vehicle to clear before attempting to complete their left turn.
The all-red clearance interval exists to provide enough time for vehicles to clear the intersection if they are unable to stop on amber. Violating it represents a major safety hazard.
That said, there is some logical basis for two of your suggestions: that streetcars can get a green earlier than left turns, and that left turns can get a green soon thereafter.
On an intersection with two-way traffic, the centre of the intersection will become clear before the edges. So with a median ROW, transit could technically get a green slightly before general traffic.
But in Ontario we calculate the all-red based on clearing the entire intersection before any subsequent phases start. In contrast, some jurisdictions such as the Netherlands calculate clearances based on the conflicting phase that follows. So if a particular movement would become clear a second earlier than another, it would get a green a second earlier. And if the stop bar is set back quite far for a subsequent movement (which it often is in NL due to side-of-road bicycle paths), then that movement would get a green a little earlier to compensate. I think this is called two-dimensional clearance timing but I can't find much documentation on it.
For example let's look at St Clair and Caledonia, a pretty typical median ROW example and calculate the clearances for cars separately from transit. Based on Ontario Traffic Manual Book 12 section 3.6, the clearance for all-way red is
t = 3.6 (W +l)/V
where W is the width of the intersection in metres, l is the length of the design vehicle (6 metres for a passenger car), V is the speed limit in km/h (50 on Caledonia) and 3.6 is the conversion factor from km/h to m/s.
From the stopbar to the far side of the crosswalk along Caledonia is 35.9m, which means that the time to clear the entire intersection is 3.02 seconds from start of amber. Clearances should always be rounded up, but this could possibly be rounded down to 3 on a judgement call.
From the stopbar to the far side of the streetcar ROW is 20.2m, which means that the time to clear the streetcar ROW is 1.88 seconds from start of amber. That would round to a 2 second all-red.
So technically streetcars could get a 1 second head start without violating all-red clearances if we used two-dimensional clearance calculations.
Because of the geometry of the interactions between the streetcars and left turns, you could probably get away without much all-red clearance between the end of the inserted transit phase and the start of the left turn phase. As you noted, it is not a safety issue, since people will not accelerate into the side of a streetcar already blocking their way. But there isn't much benefit to starting the green early, since the left turners will still be unable to proceed until the streetcar is out of their way, regardless of the colour of the light. A 6 second clearance might be a bit much for a 15 metre CLRV, but once we start running 30 metre Flexities on St Clair, even a 6 second clearance would likely have the green for left turns starting before the streetcar is out of the way. The best source of time saving would be to allow extremely short minimum greens for streetcars- maybe 4 seconds. The green would continue only until the moment the front of the streetcar crosses the stopbar, from which point the streetcar's clearance time would be consistent enough to begin the left turn exactly at the right moment (about 2 seconds before the streetcar is out of the way).
The bottom line is that while there is some logical basis for your concept, the real-life numbers simply don't work out for it to be a strategy on its own. The efficiencies you note might be able to save a second or two, but that falls well short of the dozen or so seconds it takes a streetcar driver to react to a green light and travel far enough through the intersection for left turns to proceed. In the end, what you are suggesting is basically an inserted phase with maybe a second or two saved through improved efficiency. These are valid comments regarding increasing intersection efficiency, but it doesn't change the fact that the City needs to approve the use of inserted or rotated phases to prioritize streetcars over left turns.
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