TAC is an acronym that stands for "Traffic Analysis Chart." It's a type of chart used to display and analyze traffic data, such as vehicle counts or turn volumes. The TAC chart displays the number of vehicles (or other units) passing through a location over time, typically showing hourly or daily counts. This type of chart is commonly used by transportation engineers and planners to study traffic patterns and make informed decisions about road design, signal timing, and other traffic management strategies.