Analyzing Travel Time Reliability: Data and Analysis Methods

Figure 2. Long Description

This figure shows speed estimates on a 5-mile section of I-695 in Maryland that have been derived from three different data sources and methods: (1) probe data using the snapshot method, (2) probe data uses the virtual probe method, and (3) trajectory data. Method (1) uses probe vehicle-based link travel times that are simply summed over the segment for each time interval in the data (e.g., 5-minute intervals). Method (2) simulates the movement of a vehicle probe in time and space, using the probe vehicle-based link travel times. Method (3) is based on trajectory data, which measures the movements of individual vehicles over time and space. The graph shows that the speeds over the segment are nearly identical for the probe snapshot and virtual probe methods (Methods 1 and 2). Speeds derived from vehicle trajectories are consistently higher than for the probe snapshot and virtual probe methods and also exhibits much higher fluctuations from time interval to time interval.