Flashing beacons (also called flashers or flashing lights) are frequently requested in the belief that they will reduce vehicle speeds and make drivers more alert of road conditions. Unfortunately, studies indicate that this often is not the case. Flashers can yield an initial benefit; however, they lose much of their effectiveness typically after three months. The flasher is then ignored because it becomes part of the normal driving environment. Therefore, we do not recommend the installation of unjustified flashers.
The flashing yellow arrow is part of a new signal display system that more clearly indicates to drivers when they must yield to make a left turn across traffic.
In April 2013, Cobb DOT installed a flashing yellow arrow signal at Cooper Lake Road and East West Connector in west Cobb County. As of April 2015, Cobb County has a total of 14 FYA signals.
The Department does not operate traffic signals in “flash mode” for the following reasons:
- Standard traffic engineering practice is to only flash signals for emergency conditions, or prior to a new installation. An emergency condition can occur when the electronic monitor detects a problem with the traffic signal controller and automatically places the traffic signal in flash mode.
- In general, the traveling public recognizes the signal flash mode as a malfunction and not as normal operation.
- The traveling public is unclear on how to travel through a signal in flash mode; some treat the condition as an all-way stop and others as a side street stop; and as a result a safety risk is created and unnecessary traffic delays can occur.
Alternatively, the Department accommodates side street traffic during light traffic conditions by operating signal systems in either a very short cycle length of approximately one minute, or by operating signals in “free mode” which permits a rapid change from the main street green to serve arriving side street traffic.
Including those operated and maintained by the cities of Marietta and Smyrna, there are 700 signals in Cobb County. (There are 8,200 in Georgia and 300,000 in the U.S.)
Traffic signals utilize an electronic controller to assign the right-of-way to particular traffic movements, vehicular and pedestrian, based on a signal timing plan. All traffic signals in Cobb County include vehicle detection typically in the form of an inductance loop in the pavement, a video camera or a radar device to optimize traffic flow and minimize delays. The traffic signal controller is programmed to reduce time or skip time for a phase of traffic or traffic movement based on input from the vehicle detection equipment. Some signals operate in a system or a collection of signals in a coordinated manner to further optimize traffic flow through a corridor or in an area. In general, coordinated signal systems favor the predominant direction of traffic flow.
CCDOT installs traffic signals when traffic volume and other criteria meet national standards established in the MUTCD. An engineering study, which includes analysis of vehicular volumes, pedestrian traffic, intersection safety and vehicular traffic flow, is performed to identify locations for installation of traffic signals. There are disadvantages when installing a traffic signal; therefore, we do not recommend installation when these criteria are not met. Installation of signals not satisfying these criteria may increase delays and congestion, and reduce overall intersection safety.
Yes. These requests are reviewed by Traffic Operations and must be approved for any activity that would impact traffic flow. In general, two to three weeks’ notice is required for any closure. If approved, all related traffic control must comply with Cobb County standards and the MUTCD. For lane closure permits, email [email protected] or call 770-499-4461. For road closure permits, email [email protected] or call 770-528-1676. For special events, contact the Cobb County Police Department at 770-590-5764 to request a special events permit. For requests to film in Cobb County, contact Cobb County Community Development at 770-528-2018 to apply for a film permit.
No evidence exists to show that “Children at Play” signs reduce pedestrian crashes or lower speeds. These signs could provide a false sense of security, suggesting that playing in the street is acceptable. For these reasons, along with federal guidelines and the concern that the use of unnecessary signs can promote disrespect for all signs, we do not recommend the installation of these signs.
The County offers two solutions: speed limit enforcement and traffic calming programs.
To request speed limit enforcement, please contact the Cobb County Police Department by submitting a traffic complaint.
Our traffic calming programs include installation of speed humps, on local roads with a speed limit of 25 mph, dynamic speed display signs on two-lane local and collector roads and deployment of temporary speed trailers which display a driver’s speed adjacent to the posted speed limit for instant comparison.
in Cobb County. One type of camera is used for video detection by electronic traffic signal controllers to detect whether or not a vehicle is present at a traffic signal. They do not record, and they are not routinely monitored. The second type of camera is monitored in the CCDOT Traffic Management Center for incident and event management as well as traffic signal management. These cameras are used for traffic monitoring, and the video is not recorded or archived. These cameras can be viewed at bit.ly/ccdottrafficcams.
Marked crosswalks at locations without a stop sign or traffic signal are sometimes requested to help delineate where pedestrians should cross. To request a crosswalk, please email us at [email protected] or call us at 770-528-1600. Requests will be reviewed and evaluated based on pedestrian volumes, traffic volumes, vehicular speeds, crossing width and sight distance. In the wrong location, a painted crosswalk can cause additional risks to pedestrians as safety studies have shown that simply adding crosswalks does not make crossings safer nor do they necessarily result in more vehicles stopping for pedestrians.
CCDOT collects and maintains a traffic count database for most roads within the County. The traffic count map is periodically updated and includes counts taken within the last 10 years. The count is the average daily traffic (ADT), which is a 24-hour count of vehicles for both directions of travel. GDOT also maintains a traffic count database for roads within Cobb County. GDOT traffic count data can be viewed at geocounts.com/gdot.
The Cobb County Department of Transportation (CCDOT) makes a recommendation of posted speed limits for radar and speed limit ordinances for review and approval by the Georgia Department of Transportation (GDOT) and the Cobb County Board of Commissioners. Only GDOT-approved speed limits may be enforced by Public Safety. The radar and speed limit ordinances are updated approximately every three years.
The criteria used to establish posted speed limits are based, in part, upon the characteristics of the roadways and their design speeds. The key elements include:
- Road alignment
- Sight distance
- Lengths of merges and tapers
- Road surface characteristics
- Shoulder condition
- Grade (i.e., steepness of the road)
- Roadside development
- Parking practices
- Driveway spacing
- Functional classification of the street
- Crash experience
Additionally, speed limits are established by drivers. In order for a speed limit to be effective, it must be reasonable and the majority of drivers must comply voluntarily. National studies have found that the speed at which 85% of motorists travel is reasonable and safe. This determination is made by conducting a speed survey of vehicles traveling along the roadway in question during normal operating conditions.
Studies have shown that drivers are more likely to regulate their speed based on road, traffic and weather conditions than by posted speed limits. Posting a lower speed typically will not slow traffic, without constant enforcement. State law requires posted speed limits along public roads to be at least 25 mph.
Rumble strips are raised or grooved patterns in the travel lane and/or shoulder that create noise and vibration. With proper design and construction, rumble strips may provide some traffic calming benefit. For example, shoulder rumble strips along the interstate may help prevent run-off-the-road crashes. Due to the noise created by rumble strips, we do not recommend using them to slow traffic in residential areas. The noise may alert drivers but also agitate neighbors each time a vehicle crosses the device.
A modern roundabout is a safe and efficient form of traffic control which is relatively new to the U.S., although very common throughout other portions of the world for several decades as an alternative to stop-controlled and signalized intersections. The main characteristic of a modern roundabout is the “yield-at-entry” rule, meaning that traffic entering a roundabout must yield to the traffic already within the roundabout. Roundabouts are designed for lower speeds and can have one or multiple travel lanes depending on traffic volumes. Studies have shown that roundabouts can greatly improve the capacity and safety of intersections when compared to stop signs and signals. This is primarily because of lower entry speeds, simplified decision making and fewer conflict points. Four-way intersections have 32 possible vehicle-to-vehicle conflict points, but roundabouts only have eight..
Traffic control devices are signs, signals, pavement markings and other devices that regulate, warn, or guide traffic.
The Manual on Uniform Traffic Control Devices (MUTCD) has been prepared by the U.S. Department of Transportation’s Federal Highway Administration to set forth the basic principles which govern the design and use of traffic control devices. The manual was developed with input from technical experts from many organizations, including state, county and municipal governments. It is the national standard used to provide clear and consistent guidance to the traveling public that simplifies driver decisions by promoting instant recognition and understanding. The MUTCD is available at mutcd.fhwa.dot.gov.
Traffic engineers are responsible for the installation, operation and maintenance of traffic control devices and an Advanced Traffic Management System (ATMS) for over 2,400 miles of road. The ATMS includes approximately 550 traffic signals and more than 230 closed circuit cameras for the safety and mobility of the traveling public. Traffic engineers also operate a Traffic Management Center for centralized monitoring and control of traffic signals, and to facilitate effective incident and event management, provide rapid, real-time communication of traffic conditions and facilitate traffic engineering studies.
News & Events
Two Cobb DOT Projects Recognized During GPTQ Awards
Two Cobb County Department of Transportation (Cobb DOT) projects were recognized by the American Council of Engineering Companies of Geor