Existing traffic volumes can be affected by disruptive events. During disruptive events (such as the COVID-19 pandemic or inclement weather conditions), data collected may need adjustment to account for anticipated impacts of the disruption and to remove outliers.

Options for obtaining data during a disruptive event vary based on the disruption type, duration, data availability, and data limitations. If data is less than two years old and was not collected during a recent disruptive event it can be used as is. In other situations, lack of recent counts could create the need for counts to be grown with historical growth rates or validated by big data. Big data uses geolocation services to sample the number of users on a transportation facility and their movements.

Figure 3-3

shows a decision tree to help decide what method to use for traffic analysis.