I am trying to model a single lane bridge with signalized intersections at each end. I have the simulation working in SimTraffic 5.0, but the program throws in a few midblock vehicles every once in a while. It makes the simulation function as though the timing parameters we have entered don't work, but in reality there never will be any midblock traffic entering the intersection from the center of the bridge.

We have set the midblock traffic setting on all approaches to zero, but we are still getting phantom vehicles.

Any help would be appreciated.

Thanks.

Andy

Hi Andy,

My guess is that this has to do with volume balancing. If the upstream intersection is sending less than arriving, you will see some vehicles appear.

Please note, this include the heavy vehicle mix. For instance, if you send 1000 vehilces with 2% trucks. If you enter 1000 vehilces downstream with 10% trucks, then the fleet mixes are not balanced and they should be if you don't want to see appearing/disappearing vehilces.

- John.

John Albeck
Trafficware

I am experiencing something similar to Andy's problem.

I have a small network of 3 signals and there is an external signal that I am not modeling because I have no interconnects and it has a long cycle length of 130 seconds. This signal gives me surges of vehicles and I want to model the surges. To do that I put in a dummy signal upstream of the signals with a 130-second cycle length. I want it to give me a platoon of about 20-25 cars per cycle. When I put in the appropriate volume at the dummy signal I am getting phantom cars at the downstream signal.

I realize this is a volume balancing issue and I don't mind cars appearing because the cars are coming from mid-block intersections. The problem is the cars are appearing right in the left turn bay. When this happens there often isn't room for the car and it gets thrown into the thru lane. The car wants to go left so it just waits until there is a gap blocking the thru traffic the whole time. The phantom cars are creating queues that are not realistic.

Is there anyway to force the phantom vehicles to appear farther upstream instead of right in at the signal?

Thanks,
Ryan

I figured out what my problem was. I had a short link in-between the dummy signal and the downstream signal. I couldn't eliminate the short link because it modeled a lane drop. However I added an unsignalized intersection right after the dummy intersection just upstream of the short link and balanced the volumes.

So far this seems to be working. However, I would still like to know if you could choose where the phantom cars appear. I am guessing they are set to appear at the midway point of the link.

Thanks,
Ryan

Hi Ryan,

I'm afraid there is no way to tell SimTraffic where to place the sink vehicles. Sink and Source vehicles will always appear mid-block.

Thanks,

John.