Dr. Laurence Rilett
Date of this Version
Murphy, Sean. "A Comparison Of Empirical And Highway Capacity Manual Estimated Travel Time Distributions On Urban Arterials." MASc thesis, University of Nebraska-Lincoln, 2021.
The vast majority of drivers utilize arterial roadways to travel to their destinations. The time it takes to travel on an arterial roadway can vary considerably from day to day. The factors that affect this day to day variability include weather, changes in traffic demand, crashes, incidents, work zones, and special events. As a result, there is a growing interest in the transportation field to better understand, measure, estimate, forecast, and portray this variability to both drivers and system operators. In the past, delay on arterial roadways has typically been reported using the Level of Service (LOS) concept where delay is ranked from best (e.g. LOS A) to worst (LOS F). The issue with using LOS to report delay is that the LOS is based on average travel times, which is a measure of central tendency. In reality, it is also important to utilize measures of dispersion such as travel time variance. Consequently, travel time reliability (TTR), which attempts to utilized measures of both central tendency and dispersion, has recently gained importance.
The Highway Capacity Manual is the standard manual used in the United States for estimating and forecasting arterial roadway capacity, LOS, travel time, and delay in the US. The sixth version of the HCM, known as the HCM-6, was released in 2016. For the first time, this new version included a methodology for estimating TRR on urban arterial roadways. Interestingly, the HCM-6 TTR methodology was neither calibrated nor validated using empirical data. Recently, this methodology was compared to empirical data for one urban arterial roadway in Lincoln, Nebraska. It was found that while the HCM-6 methodology matched the average travel time, it underestimated travel time variance by approximately 65 percent (1).
The research in this thesis examined five arterial roadways in the state of Nebraska to see if the HCM-6 underestimation of variability exists on other arterial roadways. The empirical travel time data for five urban arterial roadways were statistically compared to the estimated travel time distributions derived using the HCM-6 methodology. It was found that the HCM-6 methodology underestimated, on average, the mean travel time and standard travel time by 11.5% and 51.5%, respectively. Lastly, a calibration approach was applied to these five urban arterials. It was found that the HCM-6 TTR methodology, when calibrated, resulted in statistically similar results as compared to the empirical data for all five corridors.
Advisor: Laurence Rilett