Transportation System Engineering PhD student and NTC research associate Ernest Tufuor was the first author on a paper that received the 2019 Best Paper Award from the Transportation Research Board (TRB) Committee on Highway Capacity and Quality of Service. The paper was chosen from the top-ranked papers accepted for publication in TRB. After being presented to the committee at the 98th TRB annual meeting in 2019, “Validation of the Highway Capacity Manual Urban Street Travel Time Reliability Methodology using Empirical Data” was selected as the best paper.
The 6th edition of the Highway Capacity Manual (HCM-6) predicts travel time reliability by using historical data of weather and volume fluctuations with empirical data, such as volume count for one day, to provide users with average travel time for a traffic facility over an extended period of time. The research goal is to validate the HCM-6 urban street reliability methodology by comparing the distribution variation and the mean travel time values to those received from a Bluetooth travel time data set over a set period of time.
There was a gap in literature on testing the HCM-6 methodology and the project goal was to create a method for examining the prediction technology. When comparing the mean of the predicted HCM-6 travel time distribution and the mean of the Bluetooth empirical distribution, results found there were minimal practical differences, but significant statistical differences. The HCM-6 estimated distribution had considerably less variation than the empirical distribution, and the HCM-6 model underestimated the travel time reliability metrics, that is the buffer index and planning time index.
At the end of research, two augmentation strategies were proposed for the HCM-6 methodology. Those would be calibrating the model to local conditions and allowing for disaggregate input data. Work on the specifics of these strategies is currently ongoing. At the completion of the study, it is expected to provide ways to reduce estimation errors in the HCM-6 methodology and guide HCM-6 users to understand the sensitivity of the methodology to the type of data inputs.
Ernest would like to acknowledge his advisor, Dr. Laurence Rilett, on his supervision of this research, the City of Lincoln for access to data, and NTC staff members Amber Hadenfeldt and Madison Schmidt for their editorial work. Ernest and Dr. Rilett were presented the award certificate at the Washington D.C. TRB meeting in January 2020.
