Does anyone have any experience with eliminating sinking vehicles [the typical vanishing blue cars or trucks] from a SimTraffic run? I am preparing for a City Council presentation and it would not bode well for us if we have vehicles that drop out of our simulation.

As a point of reference, my overall volumes between intersections balance; the only vehicles that sink are trucks. Short of balancing the heavy vehicle percentages [I'm not even sure if that would solve the issue], is anyone aware of how to eliminate this issue?

Also, I created a parallel analysis where I *did* balance the heavy vehicles between intersectiosn and backed into the percentages in Synchro. While it happens less, it still does happen. Is there a setting in Synchro or SimTraffic I cam change to avoid this?

I tend to use uniform truck % for this very reason. I think this is a result of the truck volumes not precisely adding up when the trucks movements are recalculated at the next intersection. it could probably be explained by the whole numbers not adding up.
I think the only way to fully eliminate this would be to have trucks assigned by volume entry and not %, then truck % would be a result of the two, not the other way around.
Its not often at all I see data collected with this level of detail though. Maybe a year ago I organized a mid day count on the highway/main street in a nearby city and while I was expecting high truck % (given harvest, canning, and aggregate mining activities, in addition to though truck traffic) but was not expecting truck % as high as 36-39% on some primary movements.

Eric Royer
Caltrans

Hi Alan,

It could be a rounding issue with heavy vehicles. When percent of heavy vehicles is entered, it is to the nearest percent. When the number of trucks is calculated, it could give a non whole number. SimTraffic will need to round this. Then, downstream could round different due to a difference in turning movement percentages. This could cause a few odd vehicles to source and/or sink.

The other thing to check would be the Mid-Block flow setting in the volumes window. If this is non-zero, SimTraffic will create source/sink vehicles.

Thanks,

John.

Thanks for both responses so far. I agree that the rounding is probably the error. The issue is that this will be a very contentious meeting, and having to explain missing/sinking vehicles with a response of 'rounding' probably won't go over well. To another engineer/technical person, yes; to a City councilperson, no.

Also, I looked at my midblock numbers in the volumes window. All are zero.

Can I conclude that backing into the HV% and hoping for only a few sinks here and there is the best I can hope for?