Priority Rules

Priority Rules & Conflict Areas

The consultant should apply priority rules and conflict areas only where appropriate. Mixing priority rules and conflict areas can also cause unexpected behaviors so it is typically best to use just one. Additionally:

• Protected left turns typically do not need priority rules or conflict areas unless used to prevent blocking of an intersection.

• Excessive conflict areas can create unintended behaviors in the model.

• Protected-permissive left turns should be coded with a priority rule that  allows the flexibility to adjust observance based on which signal phases are active and which are not.

• Conflict areas are generally recommended for all other movements unless a priority rule is needed. Conflict areas and priority rules are to mimic field conditions, and the consultant should verify that they perform accordingly.

• UDOT requires roundabouts be coded according to the examples used in the Vissim user manual for priority rules and conflict areas to ensure a realistic representation of roundabout operations.

• If vehicles are queuing in a “keep clear” zones (e.g., in a signalized intersection), the consultant must apply a priority rule to enforce the keep clear zone.