Intelligent Transportation Systems Institute, Center for Transportation Studies, University of Minnesota
Freeway travel time data is used as an important input for measuring travel reliability and accessibility. The goal of
this project was to generate reliable travel time data using loop detector data from the Twin Cities’ freeway
network collected over the past 14 years for the Access to Destinations projects. Several difficulties exist: one year
of loop data can be missing up to 31.7%, loop data does not include vehicle lengths or classification to use in speed
calculations, and link travel time must be computed without knowing speed variability within the link. The three
basic approaches used in this project for imputing speed data are linear regression, spatial imputation, and week-toweek
temporal imputation. A new method was developed to estimate average vehicle length using volume,
occupancy, free-flow speed, and speed limit data. Link travel times were calculated by dividing the distance
between stations into thirds and using speed data from both stations. Overall (for the last fourteen years), the
imputation increased the average amount of valid data from 81.7% to 98.6%. Travel time for a selected route was
verified by comparing the resulting calculated travel times to manual travel times measurement information.
Intelligent Transportation Systems Institute,
University of Minnesota
Kwon, Taek Mu; Klar, Scott.
Access to Destinations: Computation of Travel Time Data for Access to Destinations Study.
Intelligent Transportation Systems Institute, Center for Transportation Studies, University of Minnesota.
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