User Guide > Arrival Turning Flows
Arrival Turning Flows
The Arrival Turning Flows (veh/hr) are displayed for Right Hand Drive with the right turning flows in the right column. Bypass flows are stored in a separate column. AM Peak, Off Peak and PM Peak flows are used in Rodel and can be used to produce Annual Economic Evaluation data for both Delays and Accidents.
The Arrival Turning Flows are modified in several ways:
- The Arrival flows are converted to passenger car equivalent flows using the Percentage of Trucks. This is essential as capacity equations use passenger car equivalent flows. This includes the effect of trucks on capacity.
- A Flow Factor, provided for each leg, is a utility factor for modifying flows for any reason. Usually it is used to growth the flows up or down to a different year, or for sensitivity testing of flow variation on Capacity Queues, Delays and Level of Service.
- Rodel includes Start Queues (the queues existing at the start of the peak hour) for both the Roundabout yield line and the Bypass lane. When VC Ratios are low/medium, Start Queues are minimal and can be ignored. However at higher VC ratios they can be significant and ignoring them can lead to an underestimation of Delays, Queues and Level of Service, when they are most critical. The Start Queue input is primarily used when modeling existing observed flows with direct flow input, as the start queues are known. If the start queues are not known, (future year flows), then zero is input and Rodel estimates the Start Queues by automatically modeling a pre peak period before modeling the peak hour. The start queues are added to the peak hour flows as these wish to cross the yield line during the peak hour.
The Arrival Flows are the average flow rate for the peak hour and must modified to create the varying flow rate due to the rise and fall in flows over the peak hour. This can be done three ways:
- Direct Flows can be input. These are observed flows counted for short equal time periods during the peak hour (1, 3, 5 or 15-minute intervals).
- A Peak Hour Factor can be used to create three flow levels with the central 15-minute section elevated, while the levels on either side are depressed. This results in a more coarse representation of the peak hour profile and is consistent with HCM procedure.
- A Synthetic flow profile can be created by reshaping the peak hour traffic flows into a Normal Distribution, that is then divided into short Time Slices to produce a fine histogram of the rise and fall in peak hour traffic. It uses three Flow Times and three Flow Ratios that allow any shaped profile to be created. It is especially useful for a factory exit where the traffic emerges for a very short but sharp peak within the peak hour.
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