Traffic Signals

Engineering Director

Thomas V. Clabo, P.E.
[email protected]
(865) 215-2148

400 Main St., Suite 475
Knoxville, TN 37902

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Traffic Signal Installations 

Traffic signals are installed within the City of Knoxville by one of three ways:

* The City of Knoxville installs a traffic signal as part of the regular signal index program.
* A developer installs a traffic signal in conjunction with a new development that justifies a signal (as approved by MPC and by Transportation Engineering Division).
* A traffic signal is installed as part of a roadway improvement project by TDOT or the City of Knoxville.

The City signal index program takes place in late January each year. A list of candidate locations for new signals are compiled throughout the previous year. Accident and traffic volume information is gathered for each candidate location. This ranked list is discussed among the Transportation Engineering Division engineers, and the most practical solutions for a signal are selected from the top of the list. 

More specifically, the volume criteria for signal installations are described in warrants published by the Federal Highway Administration (FHWA). These criteria, also described in the Manual on Uniform Traffic Control Devices (MUTCD), call for a certain volume of traffic on the main street and the side street. Accident statistics are also important, because if a location has a high number of accidents preventable by a traffic signal (such as right-angle collisions), it will be higher on the index. 

Traffic Signal Operations 

Traffic signals operations involve timing, phasing and coordination. Signals are retimed and phases are added whenever justified by engineering studies. Traffic counts are usually involved in any retiming or rephasing. 

Signal timing is based on a logic of providing as much time as possible to the major street, thus serving the larger motoring public interest. This also aids in the coordination of traffic signals. 

Signal phasing is where different traffic movements are given exclusive right-of-way by a distinct signal display. Signal phases are added as justified by engineering study, based upon traffic volumes of turning and opposing traffic. The tradeoff with added phases is that by adding a phase, time is taken away from the other movements at the intersection, increasing delays and traffic backups. 

Signal coordination is set with Knoxville's Closed Loop Signal System, which utilizes timing developed from computer traffic models, adjusted by field observation.  This system is broken up into eighteen subsystems for the following major routes: 
  • North Broadway from Foley to Adair
  • North Broadway I-640 system from I-640W exit to Powers
  • North Broadway from Raleigh/Walker to Grainger
  • North Broadway from Glenwood to Jackson
  • Henley & Western from Henley/Main to Western/Dale
  • Chapman Highway from Blount to Fronda
  • Cumberland Street from Walnut to Neyland
  • Kingston Pike from Scenic to Keener
  • Kingston Pike from Papermill to Downtown West (also includes West Towne Mall signals on Morrell and Montvue, as well as Ray Mears at Downtown West)
  • Kingston Pike from Gallaher View to Fort Sanders West Blvd (also includes Cedar Bluff from N Peters to Executive Park, and signals for the I-40/Walker Springs interchanges)
  • Middlebrook Pike from Vanosdale to Gallaher View (also includes Walker Springs at Gallaher View)
  • Western Avenue from Shoppers Lane to Texas Avenue
  • Clinton Highway from Tillery to Merchants (also includes Merchants from Schubert to the Ingles store)
  • Emory Road from I-75S exit to the Ingles store
  • Knoxville Center shopping mall (includes signals on Millertown Pike and Washington Pike)
  • Schaad Road / Callahan Road / Clinton Highway
  • 17th Street from Western Avenue to Highland Street
  • Lovell Road at I-40 / Lovell Road at Parkside Drive / westward to Baptist Hospital entrance and Herons Nest Road