Estimating Travel Time Reliability on Freight Corridors

Travel time reliability as one of the performance measures of transportation systems for moving people and goods has become of increasing importance. This paper estimates the reliability measures based on the planning time index, the buffer time index, and the reliability index that have broadly interpreted the uncertainty of travel time. The on-board global positioning system (GPS) installed on heavy-duty commercial vehicles was utilized to collect travel time and speed data. This paper also examines statistical distributions including the Gamma, largest extreme value, log-logistic, log-normal, and Weibull distributions to determine the best fit to the data of freight trips on urban freight corridors that provide access to a seaport. The results of goodness-of-fit tests indicate that the log-logistic is the best statistical function for freight travel time during the mid-day period. In addition, travel time prediction models identify the relationships between travel time, speeds, and variance-related factors that affect travel time reliability such as traffic incidents, work zones, and traffic signal breakdowns. The results indicate that traffic incidents and speed fluctuations primarily contribute to travel time unreliability for freight movement on the urban arterials.