HI,

I am having trouble understanding the application of Inhibit max feature in Synchro. The help section says

" Used for Actuated coordinated signals only. When Yes, a non coordinated phase can show more than its maximum time when it starts early".

However in real life one would like to give maximum time to coordinated main street not to side streets. The default value is set to "Yes", which gives unused time to side streets.

I was unaware with this feature as I never used it. In my example, my side streets volumes were very low, but inhibit max was set to default "yes" for the side streets with recall mode set to none for all non coordinated phases. Traffic controller was set to N/S main street Actuated coordinated. Intersection was operated under two phase with smaller Northbound advance phase.

With inhibit max set to "yes" northbound advance was getting 10 sec more than maximum time set for the phase. In this case, unused green time from side street was given to northbound advance phase not to the N/S main phase that really wanted the extra 10 sec.

I apologize for the long description, but I need to clear my mind that in which case do we really use this feature. if it hurts not help then should'nt it be defaulted to "No" all the time instead of "Yes".

Your clarification on this matter will be greatly appreciated.

Hi,

Synchro does default to Inhibit Max set to yes. What this means is that if the actuated movement starts early it COULD get extra time (not definite). One reason why the default is Yes is that some controllers on the street don't even give this option. In coordination, 170 controllers will have the user input a force off (FO) which is when the actuated phase is forced off. If the phase starts early, it could continue to its full FO time and actually give extra time to the actuated phase. Due to this controller limitation, Synchro will default to Yes to meet these cases.

The other reason may be more from a practical standpoint. In an actuated-coordinated intersection, the main street is assigned a guaranteed amount of time by the operator. What many will do is shave time from side street movements when the intersection is over-capacity and ensure that that main street gets a specific amount of time. This time is set to clear the platoon of vehicles. So, the theory here is that the main street already has been given enough time at the expense of the side street. So, if the side street gets lucky enough to start early, why not give them some bonus time if they need it (keep in mind, they will gap-out if they don’t need it).

On the statement, “However in real life one would like to give maximum time to coordinated main street not to side streets. The default value is set to ''Yes'', which gives unused time to side streets.” As noted above, the main street may still get unused time if the side street gaps out. Also, it might not even be a real option for some controllers.

On the other statement, “With inhibit max set to 'yes' northbound advance was getting 10 sec more than maximum time set for the phase. In this case, unused green time from side street was given to northbound advance phase not to the N/S main phase that really wanted the extra 10 sec.” If the northbound advance was getting the extra 10 seconds, it sounds like it “wanted” it too. Otherwise, it might have gapped out.

Of course, you can always go to the Network Settings and change the Inhibit Max for all intersections if you have a different theory. In version 7, you can even set this as your Default (Inhibit Max set to No – Unchecked). See page 2-27 of the Synchro Studio 7 User Guide if you are using this.

Thanks,

John.

It seems to me that the "Inhibit Max" Synchro setting is actually whether the coordinated signal operates with floating or fixed force offs. The inhibit max function is related to the Max Green setting, and Synchro does not have an input for Max Green; Synchro uses Total Split, which implies a max green of Split - Y - AR, but that is not always the way a controller is programmed. My understanding of how inhibit max works, from watching a controller not function the intended manner, is that Inhibit Max allows the coordinated split time to exceed the Max 1 or Max 2 time currently in effect.