Investigation of Work Zone Travel Time Reliability Using Private-Sector Data

The impact of work zones on mean travel time and travel reliability has gained increasing attention as agencies focus on performance measurement. Work zone travel time reliability has often been difficult for agencies to quantify due to the time and expense required to collect travel time data. Recently, several private sector companies have begun selling travel time data, creating an opportunity to cost-effectively examine work zone impacts on travel time reliability on a broader basis.

The Virginia Department of Transportation recently acquired probe vehicle-based travel time data for 2010 from a private sector data provider. These data were used to calculate travel time reliability measures at 15 work zones and examine factors that impacted travel time reliability. Travel time reliability was quantified by using the 95th percentile travel time, buffer index, and planning time index. The work zones saw a statistically significant degradation across all travel time reliability measures as compared to baseline conditions. The mean buffer index, planning time index, and 95th percentile travel time rate were higher by 48%, 18%, and 16%, respectively. Work zones involving lane closures experienced increases in mean buffer index, planning time index, and 95th percentile travel time rate of 67%, 23%, and 22%, respectively, despite occurring during off peak periods. Annual average daily traffic per lane and the number of access points per mile were found to have the most obvious relationships with declines in reliability at work zones.