The city wants the traffic signals to favor the direction of travel most used by commuting traffic (westbound in the a.m. and eastbound in the p.m.). How is this best done? In rereading the forum, I've noted that one can provide a wider green bandwidth by going to the time-space diagram and manually adjusting the offsets for bandwidth (but make sure to view this adjusted plan with the flows option).

Is this the way to do this? If, so could you elaborate on the part about making sure to view this adjusted plan with the flows option?

Thanks

Diahn

Hi Diahn,

Well, the nice thing is that Synchro is a PI minimizing objective function. The PI includes delays and stops. If on direction has higher volume, then Synchro will favor this direction simply because the volume weighted result will favor this direction.

Try this for yourself. Create a network of say 5 to 10 intersections. Keep all intersections as pretimed. Code volumes for just the mainstreet. Favor one direction with some volumes. Say 2000 vph in one direction and 1000 vph in the other. Perform a network cycle length and offset optimization. If you look at the TSD, you should see that the flows in the one direction appear to be flowing through better then the lighter volume direction.

Bandwidth can be a tricky issue. By just looking at bands, you may (I say MAY) falsely assume that vehicles in the band will not stop. In fact, if a queue exists at the downstream intersection prior to vehicles arriving, they may have to stop. They may also stop and get out of the band, therefore stopping at the next intersection anyway. By looking at the flows, you can see if the queues are clearing out prior to your flows getting down there.

There usually is no perfect solution. Optimizations require the analysts subjective options. A good optimization for one person is bad for another. Of course, if you are the person that has entered from the side street, you may not be in a band. Therefore, you may not view this as a good plan.

Back to the TSD. If you are viewing this, you can grab one of the timing bands and drag left or right. This will change the relative offset. You can tweak these if you think that Synchro has not given you a good band. But, I would encourage you to see how this impacts the flows (turn on flows before and after doing this). By changing the offset for a higher band, did you get the flow from the upstream intersection down earlier to just have to stop for the queue that has not cleared?

Thanks,

John.

John Albeck
Trafficware