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Urban Mobility: Breaking the Chain of Urban Traffic Congestion

A long line-up of cars creating a traffic jam. It's a familiar sight on long holiday weekends in most places around the globe. On holidays, the cause seems obvious: everybody is trying to get out of (or back into) town at the same time.

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2010/07/19

A long line-up of cars creating a traffic jam. It's a familiar sight on long holiday weekends in most places around the globe. On holidays, the cause seems obvious: everybody is trying to get out of (or back into) town at the same time.

Yet major traffic delays are not just reserved for weekends, long or short, anymore. More and more, holiday-like traffic levels are happening throughout the work week, eating up commuters' valuable time "going nowhere."

If time lost sitting in traffic is the problem, then time also holds the key to the solution. Nissan has been looking at the causes of traffic jams for many years, starting with too many vehicles converging on the same place at the same time, and developing ways to avoid congestion, such as the Web-based solution called "Vehicle Timetable," which estimates the arrival time to destinations according to predictions on traffic volume.
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Tohru Futami of the Electronic Technology Development Division at Nissan Motor Co., Ltd., is an industry leader in Information Technology (IT) and Intelligent Transportation Systems (ITS) and understands that more than just inconvenience is at stake when the traffic flow stops . He explains: "The cost of traffic congestion in Japan alone annually is estimated to reach 12 trillion yen ($131 billion, 1.07 billion Euro). Traffic jams not only induce stress, but also waste fuel and have an impact on the environment. The social problems associated with traffic congestion are many and in recent years, the causes behind it have become clear."

Avoiding Jams on the Expressway

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As anyone who has ever driven on public expressways knows, traffic jams often play out like an accordian -- squeezing tighter then opening up, then tightening and opening up again often for no discernible reason. But there are understandable causes. For example, congestion occurs easily around areas such as where downhill inclines change into uphill inclines (the "sag"), tunnels, curves and merging areas. When a vehicle in front slows down in such an area, the distance between it and the following vehicle becomes smaller -- and the driver of the second vehicle will begin to apply brakes. This single act of slowing by the first vehicle and braking by the second can cause a chain reaction of all following vehices braking, until finally one vehice comes to a standstill altogether, resulting in a traffic jam.

"An effective way to reduce traffic congestion on the expressways is to maintain the distance between vehicles. By maintaining one's distance behind the car in front, it is possible to break the chain reaction of braking that causes traffic congestion," says Futami. "According to recent research, it was found that if a car maintains a distance of at least 40 meters between it and the next car, traffic jams don't occur."

Once drivers get stuck in traffic, however, what can be done? Many people impulsively try to change into the passing lane to escape a slowdown, but this is a mistake.

"When congestion starts, the density of traffic in the passing lane increases, so staying in the driving lane can actually be faster. Changing to the passing lane only at merge points and then changing back to the driving lane is said to be the best way to get through highway congestion," he explains.

Finding The Roads (and Times) Less Travelled

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On the other hand, off the expressway, traffic congestion on regular roads occurs when the number of cars exceeds the road's capacity. At intersections with a lot of traffic, such as the intersection of two main streets, the interruption caused by traffic lights can cause a saturation of traffic, resulting in a traffic jam. Areas where traffic volume becomes concentrated, such as expressway exit and entry points or areas near busy shopping centers, are also prone to major congestion.

The solution to these types of traffic jams on regular roads is simply to avoid them. Even the busiest intersections, the ones with chronic congestion, are rarely jammed 24 hours a day. By using routes that are not congested and by using busy routes during off-peak hours as much as possible, traffic congestion can be avoided.

"In general, morning and evening rush hours, as well as the period around 2 o'clock p.m . when people finish lunch, are when traffic congestion usually occurs. If every driver made a conscious effort to avoid congested areas during these periods, traffic would become more evenly distributed, leading to fewer traffic jams," explains Futami.