Anchorage Queue Dynamics due to Fog Channel Closures at the Port of Houston

The Port of Houston, Texas, is regularly disrupted by recurring fog events that reduce visibility and result in navigation channel closures for safety reasons. These fog closures disrupt regional industry as no vessels may enter the port, a critical issue given the prominence of Houston as a freight gateway. Despite these significant impacts, fog events are relatively understudied in the port management literature. As arriving vessels wait in the anchorage area before visiting the port, anchorage queue behavior provides insights into the performance and resilience of the port system. We introduce conceptual definitions to capture the anchorage queue dynamics of a fog disruption and recovery cycle. Specifically, we define the queue growth rate, maximum recovery rate, and total recovery rate of the anchorage queue. We provide empirical evidence and derive typical values for these rates in the Houston anchorage using archival automatic identification system vessel tracking data and historic channel status records. Different fog events are categorized as single or compound events, and we compare the queue dynamics observed during fog events to those that occur during hurricanes, a more widely studied disruptive event. We identify 79 total fog events that resulted in measurable impacts on the Houston anchorage queue between 2016 and 2024. Anchorage queues typically grow at a rate of 0.82 vessels per hour (v/h) and recover at a total rate of 0.84 v/h, with a temporary ability to process vessels at a higher rate of 2.0 v/h after reopening postfog. Recovery rates show higher variance than growth rates, indicating that the system recovery is less predictable than its disruption. Our findings provide insights into maritime system performance and may help system stakeholders better understand and predict the impacts of fog events on vessel congestion and maritime freight operations.