TDOT continuously collects traffic information on Tennessee’s roadways as part of the Department's responsibility to monitor, collect, analyze, manage, and disseminate transportation data. Traffic data includes volume counts, vehicle classification counts, and speed data.
Annual Average Daily Trafic (AADT)
Annual Average Daily Traffic (AADT) volume is used throughout the Long Range Planning process. TDOT collects Average Daily Traffic (ADT), which is based on a 24-hour count. This information is transformed in AADT by using the raw traffic data, which is statistically corrected by a seasonal variation factor that considers time of year and day of the week, as well as adjustments for vehicle type, determined by seasonal and axle correction factors.
TDOT Traffic Data Collection Methods
- Temporary Count Systems
- Pneumatic Road Tubes - TDOT uses road tube counts throughout the state to collect classification and volume counts over a 24-hour period. Click here for maps of traffic count locations.
- Embedded Detection Loops (EDL) - Embedded Detection Loops are used on select Tennessee roadways for traffic surveillance purposes.
- Permanent Count Systems
- Automatic Traffic Recorders (ATR) - Automatic Traffic Recorders are used for recurring traffic counts all year round. They are continuously downloaded through cellular and IP communications and can be used within government, quasi-government, and other agencies.
Truck percentages are expressed as a part of AADT. As a Federal requirement and based on the high number of trucks traversing Tennessee’s highways, it is important that truck percentages are calculated. For more information on data collection methods, contact the Road Inventory Office.
Seasonal Factors & Axle Correction Factors
The 24-hour counts are adjusted to reflect seasonal changes in traffic volumes and are computed using historical traffic data collected from permanent count stations. Seasonal factors can be assigned to traffic counts based on the functional classification of the roadway and the month in which the counts were taken. Axle Adjustment Factors, on the other hand, are determined by using the traffic data from strategically placed classification count stations.