Link OD Volumes

Today's post is a continues our series on calibrating SimTraffic. Along with the Lane Alignment and Positioning Distances, the Link OD Volumes determine lane utilization in SimTraffic.

Located in the Volume Settings window, the Link OD Volumes window allows control over the origin and destination of two adjacent intersections. Link OD Volumes can be used to reduce or eliminate certain turn combinations, such as  preventing vehicles from turning left twice at a freeway or wide median arterial.

The Link OD Volumes window displays movement weighting factors that control how volume is allocated between input and output volumes. If you change one of the weighting factors, the other volumes will be dynamically updated to balance.

In this example, you can see that by default there are 217 vehicles making a SBL followed by an EBL, essentially making a U-turn at the interchange. In most cases, very few drivers make this type of movement. In order to calibrate the model, the second image below shows the SBL to EBL Weight reduced to 0.01, for a total of 18 vehicles making this maneuver.

Weighting factors may vary from 0 to 3. In some cases, you may need to edit multiple movements at the same intersection.

The impact may be most obvious while viewing the SimTraffic simulation, but it also impacts the arrival patterns used for analysis and optimization in Synchro. This setting is recommended for most interchanges and closely spaced intersections.