Evaluation of Freeway Traffic Data Acquisition: Technology, Quality, and Cost

Abstract

Travel time is an important piece of information to both travelers and transportation service providers, such as state DOTs and local transit agencies. In the past, Caltrans has deployed its own sensors to either directly collect travel time data or collect other traffic data that can be used to infer travel times. Such efforts carry significant costs at both the deployment and maintenance stages. With the growth of private traffic data providers, such as Waze, HERE and INRIX, it becomes feasible to have partnerships with such companies or simply purchase data from them. The accuracy, reliability, and cost of private vendor data should be evaluated before any contract can be pursued. This project is to help Caltans to assess the above aspects and inform their decisions on future procurement of travel time data. With assistance from Caltrans and INRIX and HERE, the research team collected about a month of traffic data for two stretches of Interstate 80. The data included traffic volume, occupancy and speed reported by dual loop detectors, travel times from Caltans deployed Bluetooth measurement system, and 5-minute average travel times from INRIX, HERE, and Waze. Since we have high granularity data from the Bluetooth system, the sampling rate from this system was obtained and it ranged from 5-10% in most cases. A simulation study to find the critical sampling rate under which the sample average travel time is a good (95% confidence) representation of the population’s average travel time, and the value was found to be at 5%. Consequently, the Bluetooth travel times were used as the ground truth, against which travel times provided by vendors were compared.