Analysing Your Network Model Results

Modified on: 2018-05-05 07:39:12 +1000

There are some key aspects of network output you should pay attention to for a good understanding of the network model results and to do changes to input specifications where necessary. These are summarised below. The Diagnostics reports for Sites in Network analysis will include messages related to these where relevant. Refer to Section 9 of the SIDRA INTERSECTION User Guide for a discussion on the Network Model.

Midblock Inflow and Outflow Rates
Use the Midblock Flows command in the Network Flows group of the ribbon under the Network tab to inspect Midblock Inflow and Outflow Rates. These can also be seen in the Lane Changes reports for internal approaches of Sites in the Network. In particular, high values of Net Inflow Rates can have a significant effect on results. As these result from differences in volumes specified for connected Sites, you may need to make adjustments to input Volumes for Sites in the Network.

Midblock Lane Change Rates
Inspect the lane change flow rates  for internal approaches of Sites in the Network using the Lane Changes command in the Network Flows group of the ribbon under the Network tab. High values of Midblock Lane Change Rates indicate the need to specify unequal lane use. Special Movement Classes specified making use of User Classes (Movement Definitions dialog) to allocate to specific lanes and signal phases help improving the quality of network analysis.

Capacity Constraint and Arrival Flow Rates

Use the Network Flows command choosing the Demand and Arrival options or the Lane Summary reports for Network Sites to see if the Arrival Flow Rate of any movement in the network has been reduced due to Capacity Constraint, i.e. it is less than the Demand Flow Rate. This is a result of oversaturated lanes at upstream Sites

Capacity Adjustment (Reduction) due to Lane Blockage

Use the Lane Displays and Network Displays functions in the ribbon and the Lane Blockage and Lane Summary reports for Sites under the Network tab to see if Capacity Adjustment (reduction) has applied to any movement in the Network as result of Lane Blockage.  This is usually associated with a high number of network model iterations, and may indicate a high level of Network Model Variability if associated with capacity constraint resulting in some Arrival Flows in the Network being less than Demand Flows.

Discontinued Movement Classes
Keep an eye on any Movement Class that does not exist at all Sites in your Network, e.g. in the case of Buses specified for a Bus Lane and Bus Priority Signals, or a Special Movement Class used at a freeway interchange to improve lane use estimation. Where possible, continuation of Movement Class specification will improve the model quality.

Different Approach and Exit Distances for Internal Legs of Network
Check Approch Distance and Exit Distance values for all connections of internal legs in the Network Configuration dialog.  Different Approch and Exit Distances will be indicated via orange colour connection lines and bars as well as pop-up messages.  You can also use the Approach Distances display for this purpose (Data Summary group of the Network tab ribbon).  You need to do the necessary input corrections in the Intersection input dialogs of the Sites involved.

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