We have had a number of consultants submit simtraffic outputs that utilize the default location and size for the detectors. We have had others who acutally code in the location and size of the detectors. My question is, how important to the final output is this parameter? What are the impacts if only the default detector size and locations are used?

Thanks
Wayne

Hi Wayne,

Well, my wishy-washy answer is: it depends. Let me give some cases.

1. If you are analyzing peak conditions, and traffic volumes are high, the detector locations will not have as big of impact. For higher volumes, the phases are probably maxing out, or close to maxing out.

2. Same peak conditions above, but have some lower volume movements. This is sort of the gray area. Certainly, for the lower volume movements, detector locations could impact green times, which would then impact the delay. However, these lower volumes are probably not the critical movements and you might be slightly off on the 'actual' delay. The only true way to tell, would be to try the detectors in the real location and the default location. However, the decision on whether the code the actual location may depend on the actual activity (see below categories on activities).

3. Off peak conditions, with lower volumes. It would have a bigger impact here since phases would likely gap-out more often. But then again, with lower volumes, the overall delays are likely less also.

Let me categorize some comments based on activity:

A. If you are preparing a signal timing plan, I would say get the data as accurate as possible (GIGO). This may help to minimize field adjustments and would be worth the up-front effort spent.

B. If you are doing a planning study 20 years in the future, the important thing would be consistency. If the defaults are used for all scenarios, then you are comparing apples to apples. It may not be necessary to define precise detector locations. In fact, you probably don't know the exact locations 20 years into the future.

Hope this helps.

John.

John Albeck
Trafficware