By Ryan Hanson
Traffic can be one of the least appealing aspects of urban living. No one wants to be caught in gridlock traveling to or from work. Despite an individual’s perspective, previous research shows that the traffic impeding employees’ commute may be a sign that the economy is driving forward. However, this relationship is complicated. While slight increases in congestion may be good for the economy, traffic that goes unchecked can slow delivery times, reduce workers’ quality of life, and limit employers’ access to labor, making a city undesirable and stalling its economy.
The Tennessee Department of Transportation (TDOT) coordinates the collection of traffic count data across the state. The data are recorded at collection stations along the state’s road network throughout the year and mathematically manipulated to account for vehicle types and seasonal adjustment. The final figures are reported as the annual average daily traffic (AADT) counts for each station. TDOT makes these data publicly available through an online application on its website.
Maps 1 and 2 show the location in each county of the counting stations with the highest traffic volume. Map 1 presents the traffic stations with the highest volume by county for 2016. Counties with the highest traffic counts are located around the state’s population centers. Map 2 shows the percentage change for these high-volume stations by county for 2011-2016. During the period, the stations are less concentrated around population centers and are more concentrated around the state capital and the Interstate 40 and 65 corridors. The county without color, White County, did not have its station with the highest volume installed until after 2011, so there is no percentage change data available for this time period.
Maps 3 and 4 show total AADT by county. Map 3, like Map1, has total daily traffic concentrated around the state’s population centers in 2016. Map 4 shows the percentage change between traffic stations that were in use between 2006 and 2016. This percentage change data show that the greatest traffic volume increases were in Middle Tennessee around Davidson County and in East Tennessee around Knox County.
The number of stations changes over time. Online data are available back to 1985, and the number of traffic stations throughout the state has generally increased since then. In 2016, there were 12,465 stations, 515 of which were added since 2006. A station in Haywood County was taken offline in 2015. TDOT does not specifically state the methodology by which new station locations are determined, but it may be assumed that stations are added to monitor areas of heavy or increasing traffic activity. Map 5 shows the locations of the stations that were added between 2006 and 2016. Again, increased activity was in Middle and East Tennessee.
It is difficult to use any one data set to compare different cities, and TDOT’s traffic counts are no exception. The topographic, geographic, and economic differences between the three grand divisions of Tennessee make it difficult to create equitable comparisons. However, TDOT’s traffic count data provide an additional measure to understanding economic changes throughout the state.
1M. Sweet. (2014). “Traffic Congestion’s Economic Impacts: Evidence from US Metropolitan Regions.” Urban Studies, 51(10), 2088–2110. https://doi.org/10.1177/0042098013505883.
2E. Badger. (2013, October 22). How Traffic Congestion Affects Economic Growth. Retrieved July 28, 2017, from https://www.citylab.com/transportation/2013/10/how-traffic-congestion-impacts-economic-growth/7310/.
3Annual Average Daily Traffic (AADT) Maps. (n.d.). Retrieved July 28, 2017, from https://www.tn.gov/tdot/topic/maps-annual-average-daily-traffic.
4Traffic History. (n.d.). Retrieved July 28, 2017, from https://www.tdot.tn.gov/APPLICATIONS/traffichistory.