Analysing Your Network Model Results

There are some key aspects of Network output you should pay attention to for a good understanding of the Network model results and to make changes to input specifications where necessary. These are summarised below. The Diagnostics reports for Networks and 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 Output tab to inspect Midblock Inflows and Outflows. These can also be seen in the Lane Changes reports for internal approaches of Sites in the Network. In particular, high values of Net Inflows 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 Output tab. High values of Midblock Lane Change Rates indicate the need to specify unequal lane use. Lane Utilisation Ratios can be specified at upstream or downstream Sites towards this. Special Movement Classes can be specified making use of User Classes (Movement Definitions dialog) to allocate to specific lanes and signal phases to help improving the quality of Network analysis.

Capacity Constraint and Arrival Flow Rates

Use the Movement Flows command in the Network Flows group of the ribbon under the Network Output tab 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 Approach Displays commands in the Network Displays group of the ribbon under the Network Output tab, and the Lane Blockages and Lane Summary reports for Network Sites under the Network tab to see if Capacity 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.

Continuity of Movement Classes

The Route Travel Performance report and Time Distance display for Routes with signalised Sites present results by Movement Class for Movement Classes that travel the whole Route. This condition of Movement Class continuity along the Route means that all Approach Movements that form the Route must include the subject Movement Class. To obtain results for a Movement Class that travels part of a Route, add a new Route where the subject Movement Class travels that part of the Route. This is also important for SIDRA ASSIGN traffic assignment functionality to be able to create Routes for each Movement Class between Origin - Destination (O-D) pairs.

Approach and Exit Distances for Internal Legs of Network

Use the Approach Distances display (Network Setup tab - Network Data Summary group) to check Approach Distance and Exit Distance values for all connections of internal legs in the Network Configuration dialog. This display will indicate different Approach and Exit Distances. You need to make the necessary input corrections in the Intersection input dialogs of the Sites involved.