Joint modeling of traffic incident duration components (reporting, response, and clearance time): A copula-based approach

The current study develops a trivariate framework that accommodates for inherent dependencies across the various components of incident duration. A unique ordered response model structure (sometimes referred to as grouped ordered response model) is introduced for modeling three durations—reporting time, response time, and clearance time—in this study. Further, as opposed to employing a simulation oriented multivariate model approach, the study proposes and estimates a copula-based methodology that allows for a closed-form probability computation. The approach is the first application of this model for incident duration analysis. The proposed copula framework is estimated to identify factors affecting incident duration components from a host of characteristics including incident characteristics, traffic conditions, roadway, and environmental characteristics. The data for the analysis are obtained from the 2015 Florida Department of Transportation incident database. The model estimates were also augmented by conducting policy analysis by generating a three-dimensional representation of incident frequencies as a function of reporting, response, and clearance time. Traffic congestion can generally be attributed to either recurring or nonrecurring events. Congestion arising from recurring events is generally a result of mismatched transportation demand and supply (or capacity). Nonrecurring congestion, on the other hand, is a result of unexpected (or irregular) events such as abandoned vehicles, adverse weather, spilled loads, highway debris, and traffic crashes. The potential solutions for congestion arising from these two sources are vastly different. This research focuses on nonrecurrent congestion. Nonrecurring congestion is responsible for approximately one-quarter of all traffic delay on U.S. roadways (1). According to Roper (2), every minute that a freeway travel lane is blocked results in 4–5 minutes of traffic delay after the incident is cleared. The U.S. Department of Transportation Strategic Plan for Fiscal-Year 2010–2015 reports that 2.8 billion gallons of gasoline are consumed every year in the U.S. as a result of incident-related congestion events (3). Moreover, longer incident durations can increase the risk of secondary incidents (4). Consequently, transportation agencies are developing traffic incident management strategies to reduce the overall duration of incidents to minimize their impacts on travelers and the environment. The overall incident duration, as identified by the Highway Capacity Manual (5), is composed of the following four phases: notification time, response time, clearance time and traffic recovery time (6). Incident clearance (third phase) is usually the longest component of the incident duration time (4). The traffic recovery time (fourth phase) is a function of total duration of the first three phases and the traffic demand on the facility. Given the importance of different phases of incident duration, the objective of the proposed research effort is to study the factors influencing incident reporting, response, and clearance times—with a goal of reducing the congestion impacts of nonrecurring events while providing improved traffic incident management plans. An important factor affecting incident clearance is the response personnel involved. In the state of Florida, in addition to the traditional agencies, a road ranger service patrol assists in the incident clearance process. In particular, Florida Department of Transportation (FDOT) offers a unique service via road ranger service patrol to offer free assistance to road users on highways to reduce delay while enhancing safety for the public. Since its inception, the Road Rangers (RR) service has offered nearly 4.3 million assists (7). The objectives of the program include reducing traffic crashes, assisting the Florida Highway Patrol to reduce incident duration, providing assistance to disabled or stranded vehicles, removing road debris, and increasing safety at incident sites. Toward meeting these goals, the RR trucks monitor congested areas and high-incident locations of the urban expressway for different nonrecurrent incidents. This research examines incident clearance duration with a specific emphasis on the impact of RR service patrol program. The analysis would allow recommendations to be made on the performance of the RR patrol while offering recommendations for similar programs in other states.