You get in your vehicle, pull out of your driveway and head on your way.

Then you get stopped by a red light. You travel a little more and you stop again — and again.

It may seem like the light gods are punishing you, but in reality, it’s all science.

“Traffic signals that are in close proximity to each other are typically coordinated to allow a (line of traffic) to progress efficiently through,” said Scott Puckett, Hall County traffic engineer.

“All of the signals within a coordinated network are controlled by a master controller, which evaluates the traffic in real time and controls the network to address the needs. Rural or isolated intersections typically operate in ‘free’ mode and the signal is only concerned with the needs of that particular intersection.”

If you feel as if you are spending too much time at a red light and not enough time moving through a green light, that, too, is based on patterns.

“Our staff compiles traffic counts by using automatic traffic counters and by taking hand counts,” said Dee Taylor, traffic engineer for the Gainesville. “These studies help us determine how long we can (make the green lights) and at the same time not negatively affect other approaches to the intersection.”

Random traffic studies also help officials determine where and if a signal is needed in a given area.

“The installation of a traffic signal must be justified based on federal guidelines outlined in the Manual on Uniform Traffic Control Devices,” Puckett said.

“We would complete an engineering study of traffic conditions, pedestrian characteristics and physical characteristics of a location and apply our findings to (those federal requirements).”

“Based on the outcome of the study and engineering judgment, if a signal is justified, we would recommend the installation to the (Hall County) board of commissioners.”

Both the city and county departments use sensors to determine if a signal cycle can be shortened if a car is the only one waiting at a given point.

Puckett said two type of sensors are used to detect vehicles at intersections with lights: inductive loops, which are installed within the roadway, or video detection cameras installed overhead.

“Either method, or a combination, is used to detect vehicles on the side street, alerting the signal controller that the side street needs to be serviced,” Puckett said. “If no vehicles are waiting on the side street, the signal typically stays green on the main line.

“Vehicle detection is also used on the main line, generally set back several hundred feet from the intersection, to gauge the density of traffic. These detectors can hold the signal green on the main line if necessary before servicing the side street.”

In addition to traffic density, traffic signal timing is also affected by the time of day.

The city runs multiple signal patterns throughout the day. There’s a pattern for early morning, pre-noon, afternoon, early evening and evening, Taylor said.

The county also has the ability to run multiple patterns.

“Periodic evaluations are performed at signalized intersections to evaluate traffic patterns and the timing would be adjusted accordingly to maximize efficiency,” Puckett said.

“For example, a nearby school may overload the roadway network for a couple of hours in the morning and afternoon. Traffic signals could be programmed to accommodate this event and then revert to normal timing.”