Dynamics of urban network traffic flow during a large-scale evacuation

Ali Zockaie, Hani S Mahmassani, Meead Saberi, Ömer Verbas

Research output: Contribution to journalArticlepeer-review

13 Scopus citations


This paper explores some of the dynamics of urban network traffic flow during a large-scale evacuation in the context of the Network Fundamental Diagram (NFD). The structure of the evacuation demand can significantly affect network performance. A radial-shape structure results in a more stable network recovery compared to a directional evacuation structure. This study also confirms the existence of the unloading-reloading hysteresis when a network is subject to successive cycles of loading and unloading. If a network undergoes a complete or near-complete recovery, the reloading path in the NFD follows almost the same path as in the initial loading. Results also suggest that the linear relationship between average network flow and trip completion rate does not always hold as it was previously thought. The relationship becomes highly scattered and non-linear when the network is highly congested, under disruption and the number of adaptive drivers is sufficiently large. Frequent route switching by adaptive drivers can artificially increase the average network flow but does not necessarily increase the network output (trip completion rate). Adaptive driving increases fluctuations in the NFD; however, it reduces hysteresis and gridlock while increasing network capacity.

Original languageEnglish (US)
JournalTransportation Research Record
Issue number1
StatePublished - Jan 1 2014

ASJC Scopus subject areas

  • Civil and Structural Engineering
  • Mechanical Engineering

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