Automated Traffic Signal Performance Measures icon

Frequently Asked Questions

There are two ways to navigate the GDOT signal performance metric website

  1. Zoom in on the map and click on the desired intersection.
  2. Select the available metric on the map from the list of available metrics for the desired intersection.
  3. Click a day and/or time range from the calendar.
  4. Click “Create Metric”. Wait, and then scroll down to see the data and charts.
  1. Select the metric by clicking the checkbox for the desired metric.
  2. Click the “Signal List” bar at the top of the map window.
  3. Click “Select” next to the desired intersection.
  4. Click a day and/or time range from the calendar.
  5. Click “Create Metric”. Wait, and then scroll down to see the data and charts.
Signal performance metrics show real-time and a history of performance at signalized intersections. The various metrics will evaluate the quality of progression of traffic along the corridor, and displays any unused green time that may be available from various movements. This information informs GDOT of vehicle and pedestrian detector malfunctions, measures vehicle delay and lets us know volumes, speeds and travel time of vehicles. The metrics are used to optimize mobility and manage traffic signal timing and maintenance to reduce congestion, save fuel costs and improve safety. There are several metrics currently in use with others in development.
The traffic signal controller manufactures (Econolite, Intelight, and some others) wrote a “data-logger” program that runs in the background of the traffic signal controller firmware. The Indiana Traffic Signal Hi Resolution Data Logger Enumerations ( encode events to a resolution to the nearest 100 milliseconds. The recorded enumerations will have events for “phase begin green”, “phase gap out”, “phase max out”, “phase begin yellow clearance”, “phase end yellow clearance”, “pedestrian begin walk”, “pedestrian begin clearance”, “detector off”, “detector on”, etc. For each event, a time-stamp is given and the event is stored temporarily in the signal controller. Over 125 various enumerations are currently in use. Then, using an FTP connection from a remote server to the traffic signal controller, packets of the hi resolution data logger enumerations (with its 1/10th second resolution time-stamp) are retrieved and stored on a web server at the GDOT Traffic Operations Center about every 10 to 15 minutes (unless the “upload current data” checkbox is enabled, where an FTP connection will be immediately made and the data will be displayed in real-time). Software was written in-house by Utah DOT that allows us to graph and display the various data-logger enumerations and to show the results on the GDOT Signal Performance Metric website.
A central traffic management system is not used or needed for the GDOT Traffic Signal Performance Metrics. It is all being done through FTP connections from a web server through the network directly to the traffic signal controller which currently has the Indiana Traffic Signal Hi Resolution Data Logger Enumerations running in the background of the controller firmware. The GDOT Traffic Signal Performance Metrics are independent of any central traffic management system.
The GDOT Signal Metric software was developed in-house at Utah DOT by the Department of Technology Services. Purdue University and the Indiana Department of Transportation (INDOT) assisted in getting UDOT started on this endeavor.
The Purdue coordination diagram concept was introduced in 2009 by Purdue University to visualize the temporal relationship between the coordinated phase indications and vehicle arrivals on a cycle-by-cycle basis. The Indiana Traffic Signal HI Resolution Data Logger Enumerations ( was a joint transportation research program (updated in November 2012 but started earlier) that included people from Indiana DOT, Purdue University, Econolite, PEEK, and Siemens.

After discussions with Dr. Darcy Bullock from Purdue University and INDOT’s James Sturdevant, UDOT started development of the UDOT Signal Performance Metrics website April of 2012.
GDOT’s goal is transparency and unrestricted access to all who have a desire for traffic signal data. Our goal in optimizing mobility, improving safety, preserving infrastructure and strengthening the economy means that all who have a desire to use the data should have access to the data without restrictions. This includes all of GDOT (various divisions and groups), consultants, academia, MPO’s, other jurisdictions, FHWA, the public, and others.
The signal performance metrics are an effective way to reduce congestion, save fuel costs and improve safety. We are simply able to do more with less and are more effectively able to manage traffic every day of the week and at all times of the day, even when a traffic signal engineer is not available. We have identified several detection problems, corrected time-of-day coordination errors in the traffic signal controller scheduler, corrected offsets, splits, among other things. In addition, we have been able to use more accurate data in optimizing models and doing traffic studies, and have been able to more correctly set various signal timing parameters.
Although the GDOT Signal Performance Metrics cannot guarantee you will only get green lights, the system does help make traveling through Georgia more efficient. GDOT Automatic Signal Performance Measures have already already helped to reduce the number of stops and delay at signalized intersections. Continued benefits are anticipated.
Yes, GDOT Signal Performance Metrics has already saved Georgians time and money. By increasing corridor speeds while reducing intersection delays, traffic signal stops, and the ability to monitor operations 24/7.
By reducing congestion and reducing the percent of vehicles arriving on a red light, GDOT Signal Performance Metrics helps decrease the number of accidents that occur. In addition, we are better able to manage detector failures and improve the duration of the change intervals and clearance times at intersections.
GDOT Signal Performance Metrics are designed to increase the safety and efficiency at signalized intersections. It is not intended to identify speeders or enforce traffic laws. No personal information is recorded or used in data gathering.
We can estimate that each signal controller requires 11 MB of storage space each day. For the GDOT system, that means roughly 10 GB of data growth every day.
Purdue Coordination Diagram     Setback count (350 ft – 400 ft)
Approach VolumeSetback count (350 ft – 400 ft)
Approach SpeedSetback count (350 ft – 400 ft) using radar
Purdue Phase TerminationNo detection needed or used
Split MonitorNo detection needed or used
Turning Movement CountsStop bar (lane-by-lane) count
Approach DelaySetback count (350 ft – 400 ft)
Arrivals on RedSetback count (350 ft – 400 ft)
Travel TimeHistorical INRIX or HERE Data

Signal Performance Metrics will work with any type of detector that is capable of counting vehicles (i.e. loops, video, pucks, radar). The only exception to this is the speed metric, where GDOT’s Signal Performance Metrics for speeds will only work with the Wavetronix Advance Smartsensor). Please note that two of the metrics (Purdue Phase Termination and Split Monitor) do not use detection and are extremely useful metrics.
Some metrics have different detection requirements than other metrics. For example, for approach speeds, GDOT uses the Wavetronix Advance Smartsensor radar detector. This same detector is what we use for our setback counts 350 feet – 400 feet upstream of the intersection. In addition, we are also able to pull the raw radar speeds from the sensor back to the TMC server for the speed data. Not all intersections have the Wavetronix Advance Smartsensors, therefore we are not able to display speed data, as well as the PCD’s, approach volume, arrivals on red or approach delay at each intersection.

The turning movement count metric requires lane-by-lane detection capable of counting vehicles in each lane. Configuring the detection for lane-by-lane counts is time consuming and takes a commitment to financial resources.
System Requirements: Operating Systems and Software: The UDOT Signal Performance Metrics system runs on Microsoft Windows Servers. The web components are hosted by Microsoft Internet Information Server (IIS). The database server is a Microsoft SQL 2008 server. Storage and Processing: Detector data uses about 40% of the storage space of the GDOT system, so the number of detectors attached to a controller will have a huge impact on the amount of storage space required. Detector data is also the most important information we collect. We estimate that each signal will generate 11.4 MB of data per day. The amount of processing power required is highly dependant on how many signals are on the system, how many servers will be part of the system, and how many people will be using the system. It is possible to host all of the system functions on one powerful server, or split them out into multiple, less expensive servers. If your agency decided to make the performance metrics available to the public, it might be best to have a web server separate from the database server. Much of the heavy processing for the charts is done by web services, and it is possible to host these services on a dedicated computer. While each agency should consult with their IT department for specific guidelines on how to best deliver a secure, stable and responsive solution, we can estimate that most mid-range to high-end servers will be able to handle the task of hosting and creating metrics for most agencies.
You can contact GDOT’s Assistant State Traffic Engineer, Alan Davis at or phone at 404-635-2832 to find out more information about Automatic Signal Performance Metrics.
You can download the source code here.
GDOT makes no guarentee for the accuracy and reliability of the data represented and provided by this system. This application and data is primarily intended for measuring traffic signal performance.