Common practice in Ontario for Protected/Permissive left turn phasing is to use a setback detector 10 meters (approx 33 ft.) back from the stop-bar such that the left turn phase is called only when there are 3 or more vehicles queued to turn left. We assume that when there are 2 or fewer vehicles queued, they will clear during the green ball (or at minimum sneak during the yellow interval). We either use a second detector at the stop bar, or place the through movement on recall to ensure that vehicles don't become trapped.

Is it possible to model this scenario?

Thanks,

Jason

This message has been edited. Last edited by: JasonB,

Hi Jason,

I'm afraid that this type of set-back detection cannot be done with Synchro or SimTraffic. A call only detector will always be placed at the stop-bar.

This is used at other places in North America also. It is something that is being considered for future versions, so thanks for the suggestion.

John.

I wanted to follow up on JasonB's original question now that Synchro 7 is out. I am trying to model the same type of left turn prot+perm phasing in v7. I have set up a four-way intersection where volumes are symmetrical (i.e., the main street has 75 lefts per hour in both directions, and 2000 throughs over two lanes in both directions), but the detector setup is different. For the southbound left, I have left the default settings (a single call+extend detector at the stop bar). For the northbound left, I have changed it to a single call+extend detector set back 15 metres from the stop bar.

When I model in SimTraffic, it appears to simulate correctly -- i.e., the southbound left phase is called even if there is only one vehicle queued, but the northbound left phase is only called for a queue of three vehicles or more. However, in Synchro there is no difference in delay, v/c or queues between the two directions, and there is no difference in the percentile green times in the phasing window.

Am I missing something, or is this a setup that can only be assessed through simulation and can't be analyzed using Synchro?