Upper-hand management

April 2, 2018
New system allows Georgia DOT to stay on top of traffic mobility

About the author: Lee is the TMC operations manager, URS Corp.; Bradford is the TMC manager for the Georgia Department of Transportation.


The Georgia NaviGAtor transportation management system has increased safety and efficiency on more than 220 miles of freeway in Atlanta’s metropolitan area through the use of a variety of applied technologies, including advanced signage, video, computer and communications systems.

The Georgia DOT Transportation Management Center (TMC), the central hub of the NaviGAtor system, serves as the basis for statewide traffic and incident management. The NaviGAtor system integrates the management of freeway and surface streets, allows state and local engineers to interact and participate in real-time transportation decisions, provides a high-speed, high-capacity communications network and acts as a clearinghouse for traveler information. Its elements include intelligent transportation infrastructure components, freeway management systems, transit management systems and incident management programs.

Closely coordinated with transportation control centers (TCCs) and emergency service providers located throughout the metropolitan area, NaviGAtor is intended to achieve a seamless transportation network across multiple jurisdictions. The system relays information to the public through its many components, allowing motorists to make efficient and time-saving transportation decisions.

The observation deck

A primary function within the TMC is the routine monitoring of traffic flow. Observation of unusual patterns of reduced speed, congestion or other interruptions of the normal flow may indicate a temporary reduction in capacity due to an incident, closure of lanes for construction or excessive demand. Even when congestion is expected, it is still necessary to monitor its extent, because a secondary problem might have occurred. Effective monitoring of traffic flows requires the use of various tools in the TMC, such as closed-circuit television (CCTV), vehicle detection systems (VDS), presence detection systems (PDS) and geographic information systems (GIS).

CCTV: Video images from CCTV cameras are used to assess the cause and status of non-recurring traffic congestion such as planned construction, verify the existence and location of traffic incidents or monitor recurrent traffic congestion. Video images make it possible to identify problems and respond in a timely and efficient manner. A prompt response reduces the potential for a secondary incident and enables TMC operations personnel to transmit traffic information to the public through the traveler information system.

VDS: The basic tool for obtaining traffic-flow information such as volumes and speeds and occupancy is a video surveillance system called VDS. The system consists of remote electronic sensors (cameras) which send video to processors located in the field. These processors convert the video into traffic data which are relayed over a communication system to a central processing location within the TMC. The VDS focuses on all lanes, providing quantification of traffic volumes, occupancy and estimates of average vehicle speed separated by direction and lane. Summary reports are compiled at a central computational processor within the TMC and displayed as either textual and numerical values or as various graphical depictions. This information is used in travel management decisions and published on the NaviGAtor website.

PDS: PDS, which is located on I-85, is used for safety purposes in the event of a lane blockage such as a stall or an accident in the high-occupancy vehicle (HOV) lane. It allows for detection, rapid notification to the TMC and placement of automatic warnings on changeable message signs. PDS cameras are fixed cameras focusing on HOV lanes and the left shoulder. Video Processing Units (VPUs), similar to the VDS processors, receive the video feed and are programmed to recognize stopped vehicles. The detection cameras, rather than surveillance cameras, are used to provide a view of the incident and, if multiple alarms occur, the video will attempt to display the situation at the front of the line of stopped vehicles.

GIS: The GIS is used as a tool to manage traffic congestion and incidents and provide information to the traveling public. Through a combination of graphics and symbols arranged in a map display of a given region, TMC operators can monitor various ITS devices and manage incident response. The graphics are used in conjunction with the NaviGAtor software interface to perform a variety of functions. The main components of GIS are a map display consisting of one or more individual map windows and a speed monitor that enables the operator to review the current speeds of traffic along certain sections of the freeway.

The control factor

Three basic concepts are employed in controlling traffic: changeable message signs (CMS), highway emergency response operator (HERO) units, and ramp metering.

CMS: These signs are among the most publicly visible components of the NaviGAtor system. They make it possible to communicate close to real-time information to drivers. Deployed at key locations along interstates and surface streets, they relay up-to-date traffic conditions to motorists so they can make informed decisions about their trip, thus easing congestion. The manner in which the CMS system is used depends on the nature of road or traffic conditions. Various categories include: travel-time information, incidents (accidents, stalls or roadwork), unusual road and driving conditions (winter weather, fog, unexpected congestion), large construction projects, major events, HOV usage and Amber alerts. CMS already has proven to substantially reduce congestion and the frustration levels of motorists.

HERO: HEROs are intended to minimize the disruption of normal traffic flow at the site of an incident and to expedite the cleanup and removal of any congestion-causing incident on the interstate system. HEROs also assist state patrol, fire and emergency medical service personnel on the scene at roadway emergencies. When not attending to an incident, HEROs are available to help stranded motorists with minor mechanical problems such as flat tires or dead batteries. They also provide fuel, coolant, road and travel information, and courtesy use of a cellular phone for emergency calls.

Ramp metering: Ramp meters are traffic signal devices used to control the flow of traffic onto freeways to reduce congestion; they are typically installed on entrance ramps of heavily traveled freeways. During peak hours or as a potential countermeasure to major incidents, ramp meters are used to control the number of vehicles entering the freeway from an entrance ramp. Vehicles are released to enter the freeway at rates that are dependent upon the controller programming and the level of congestion on the freeway segment upstream of the ramp meter. The controlled flow at the ramp meter enables vehicles to merge with through-traffic while minimizing the disturbance to the speed and safety of vehicles in the mainline lanes.

Here’s the info.

Providing traveler information is the principal interface between the TMC and the public.

The news given out to the public and media is limited to traffic-related information and never includes reports of fatalities or the status of those injured. The general run of information includes: Whether the accident is blocking the roadway and, if so, which lanes are blocked; the number of vehicles involved; how long the blockage is expected to last; how far the backup extends; alternative routes available or where traffic is required to exit if the freeway is closed; and the protocol to be followed in the event of an Amber alert.

The NaviGAtor website is accessible to the public and provides real-time information, including maps, descriptions of incidents, estimated trip times and weather conditions that might affect travel. The NaviGAtor system also offers a free statewide traveler information service—*DOT—which is available to travelers 24 hours a day.

At the workplace

In addition to monitoring and controlling traffic flows, the TMC also conducts construction work-zone management. Through effective management in the work zone, construction information is disseminated to the motoring public in a timely manner and the HERO units are dispatched to patrol work zones that may not routinely be patrolled outside of the construction project, enhancing travel safety and transportation efficiency. Traffic Interruption Reports submitted by the various construction project managers are collected in the Operations Center of the TMC. The console operator working the construction desk enters the site as a “confirmed incident” in the NaviGAtor system when the construction closures begin, and appropriate action is taken.

The NaviGAtor system, through the TMC, keeps traffic moving along Georgia freeways. In the process, it has resulted in a sharp reduction in traffic accidents, easing congestion and creating a more efficient transportation network.

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