Arterial Roadway Travel Time Reliability and the COVID-19 Pandemic

Abstract

This paper evaluated the effect of the COVID-19 preventive orders on arterial roadway travel time reliability (TTR). A comparative analysis was conducted to examine average travel time distributions (TTD), and their associated TTR metrics, before and during the COVID-19 pandemic. Travel time data for four urban arterial corridors in Nebraska, disaggregated by peak period and direction, were analyzed. It was found that in 2020, the average TTD mean and standard deviation values for all 16 scenarios were reduced by an average of 14.0% and 43.4%, respectively. The travel time index, the planning time index, the level of travel time reliability (LOTTR), and the buffer index metrics associated with these TTDs were reduced, on average, by 14.0%, 19.7%, 3.5%, and 35.0%, respectively. In other words, whether the test corridors were more reliable during the pandemic was a function of which TTR metric was used. The paper concludes by arguing for a fundamental change in how arterial TTR is measured and reported to different user groups.

Validating and Calibrating the Highway Capacity Manual Arterial Travel Time Reliability Methodology

“…That is, the LOTTR metric is insensitive to the underlying TTD. Similar results were found in a reliability analysis related to the Covid-19 pandemic (15). For this reason, the authors do not recommend using any of the TTR metrics without first validating the underlying TTD.…”

“…Because they are all positive it indicates that the TTD for each scenario is positively skewed. Note that most arterial TTDs are positively skewed (6,(15)(16)(17).…”

“…It may be seen that the average difference between the empirical TTI and the corresponding HCM6-estimated TTI value was 10.6% and ranged from 0.4% to 31.0%. Because the TTI is a measure of how the mean TT relates to free-flow TTs, it indirectly assumes that a more reliable corridor is one that has the mean TT closer to the free-flow TT, all else being equal (15). Consequently, while the empirical and HCM6-estimated TTDs are considerably different their means were not-and therefore neither were their respective TTI values.…”

“…It should be noted that the BI and the COV essentially measure the same component of reliability. That is, both measure the ratio of a measure of dispersion to a measure of central tendency (15). Given that the percentage differences in the measures of dispersion were greater than the differences in the measures of central tendency, the BI and COV had the greatest differences when the HCM6estimated TTR metrics were compared with the observed TTR metrics.…”

A Descriptive Analysis on the Impact of COVID-19 Lockdowns on Road Traffic Incidents in Sydney, Australia

“…For example, cities such as Milan, Paris, Madrid and Manchester saw a reduction in congestion by 85%, 84%, 83%, and 76%, respectively, during the lockdown period compared with the baseline scenario [ 1 ]. The reduced traffic movement has resulted in a reduction in fuel consumption [ 2 ], road crashes and fatalities [ 3 , 4 , 5 , 6 ] and air pollution [ 7 , 8 ], and an increase in travel time reliability [ 9 ]. On the other hand, lockdowns have also been associated with more frequent harsh acceleration and braking events, mobile phone usage [ 3 ], and increased crash severity [ 4 ].…”