Assessing the Effect of Traffic Incident Management Areas on Highway Capacity

Traffic Incident Management Areas (TIMAs) are established to facilitate emergency response and restore traffic flow following roadway incidents. However, lane closures within TIMAs significantly impact roadway capacity, requiring an analysis of capacity reduction across different closure scenarios. This study examines the effects of one-lane, two-lane, and three-lane closures on traffic flow and capacity reduction. Data was collected from select locations along the I-4 and I-95 corridors, in Florida between January 2023 and June 2024. Observation locations were predominately on rural freeway segments. One-lane closures made the majority of observations with 41 incidents analyzed and an average duration of 26.5 minutes. Of these, 59 percent exhibited measurable impacts on traffic flow, while the remainder showed no significant speed/flow reduction or density increase. The capacity reduction results suggest that a 1-lane closure results in a capacity reduction between 50-60% on the segment. Two-lane closures had the highest observed variability in duration, with a median of 20 minutes but a range of 131 minutes. Due to a limited sample size (12 incidents), capacity reduction calculations for two-lane closures were inconclusive. Three-lane closures, where only the shoulder remained open, were rare; with only five observations recorded along I-4. Observed flow rates on the shoulder ranged from 72 to 924 veh/hr, averaging 583 veh/hr—lower than post-recovery flow rates. Key limitations include the restricted dataset, reliance on predominately rural, three-lane freeway segments, and the need for incidents to occur near detectors. Capacity reduction calculations based on the 15-minute recovery period flow rates proved unreliable. Future research should expand the dataset, explore urban settings, and utilize higher-resolution flow rates to refine capacity estimation methodologies.