Evaluation of DOTD’s Existing Queue Estimation Procedures

Louisiana Department of Transportation and Development (DOTD) requests that freeway lanes should not be closed for construction work during hours when capacity exceeds 1,309 pcphpl. It is not known how accurate this 1,309 pcphpl value is when compared to actual queuing related to real world work zones in Louisiana. This study provided literature on how work zone capacities have been defined by different researchers and practitioners, and what factors affect such capacities. It further provided an overview of the HCM 2000 work zone capacity model and how that was used as basis for the 1,309 pcphpl threshold. A nationwide survey revealed that approximately half the number of states that responded enforced a similar threshold for lane closures, ranging from 1,100 – 2,000 pcphpl. A statewide survey revealed that majority of DOTD districts regularly performed queue analysis for work zone lane closures on freeways but perceived the 1,309 pcphpl threshold to be too high. This study determined an average field observed work zone capacity of 1,310 pcphpl, corresponding to an average queue duration of 120 minutes, and an average queue length of 1.30 miles. HCM 2016’s work zone capacity model slightly overestimates (average 6%) the capacity at Louisiana work zones but will provide representative ranges in the absence of field collected data. The study further determined a new threshold of 1,052 pcphpl as corresponding to 30 minutes of queueing conditions.