![]() However, if we zoom out on dense urban areas, not even traffic light coordination has much of an effect on the average speed of the network. The ideal grid has long blocks and short green lights, minimizing the spillback effect. ![]() Spillback is the phenomenon that occurs when cars move forward because their light turned green, but end up blocking intersections because the next light is still red. If the lights aren’t synchronized efficiently, spillback can happen. Short blocks mean a lot of stopping and starting, which is a recipe for traffic disaster. In downtown areas, traffic is mainly influenced by the length of city blocks and the timing of green lights (called green time ). In these cases, slight variations from driver to driver lead to minute braking and acceleration, which become magnified as following cars react. In other situations, traffic jams seemingly appear out of nowhere. In fact, lane-changing activity is the main contributor to capacity drop. It’s made worse when other cars start to change lanes, causing disruptions across multiple lanes. Consider the on-ramp scenario: when vehicles enter the freeway, they’re typically going slower than the rest of traffic, creating small disturbances in flow. The unifying factor in all traffic jams is human error. ![]() Freeway on-ramps, accidents, and rubbernecking are obvious culprits. In order to apply what they know, researchers must first understand what causes traffic in the first place. For example, researchers can look at the diagram below and find the optimum density of cars for maximum flow or the least traffic (labeled with a red star). From this, they can glean the average speed and travel time for any given path. Once researchers have obtained a diagram for a specific network, all they need to know to understand current road conditions is the number of vehicles on the road, which they can count with loop detectors. Every city or “network” of roads has a unique set of properties that give it a characteristic fundamental diagram, meaning that the diagrams for Atlanta and Los Angeles will be different. To understand factors that contribute to changes in capacity on a macroscopic scale, he and other theorists utilize fundamental diagrams, created using data collected by loop detectors (those pairs of black cables laid across the road). It could mean twice the delay,” explains Dr. It doesn’t sound like much, but in queueing systems like these, that’s a huge difference. “When drops, it goes down by typically 10-20%. Because of varying road conditions like accidents or lane changes, this number might drop, causing a disproportionate effect on traffic. Capacity refers to the maximum number of vehicles that may pass a given point on a road during a given period of time. Take, for instance, the concept of capacity drop. “You’re a driver, so you experience it every day,” says Dr. Srinivas Peeta (Georgia Tech) which helps researchers better understand human driving behavior.Īlthough these researchers use sophisticated simulations and math to understand traffic patterns, one does not need a PhD in civil engineering to understand the real-world effects of congestion. The Autonomous and Connected Transportation Driving Simulator Laboratory (ACT-DSL), a driving simulator in the lab of Dr. He’s among a handful of transportation researchers at Georgia Tech and part of the Georgia Transportation Institute, a consortium of researchers at various universities working in policy and planning, environmental issues, transportation technology and infrastructure, and traffic operations. Laval, who has been studying transportation for twenty years, uses this technology to study traffic patterns. Since then, new models and technology have enabled research through advanced simulations of driver behavior. Engineers began measuring traffic flow with cameras and appropriated fluid mechanical concepts to describe the patterns they observed, likening traffic to the flow of water in rivers. The field of traffic theory can trace its roots back to the mid-twentieth century, shortly after cars gained popularity. Jorge Laval, a civil engineering professor at Georgia Tech who specializes in transportation, to find out more. However, like with most modern-day problems, there are teams of scientists and engineers heroically searching for ways to improve our lives. Atlanta is also the fourth fastest-growing city in the country, meaning our roads will have to support increasingly more commuters year over year. On average, drivers lose 97 hours and $1,348 each year just stuck in traffic. Atlanta is the 11 th most congested city in the country, and most ATLiens are familiar with the frustrating ballet of rush hour traffic. ![]()
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