![]() On a four-lane stretch of the M25 this would mean 8,000 cars per lane per hour. Theoretically, in order to keep a constant flow of 60mph, the ideal number of cars on a road should be between 1,800 and 2,000 per lane, per hour. However, even with the best technology in the world, sometimes demand on roads is just too high and jams are unavoidable. Further back, a 40mph limit is set at the rear of the predicted congestion zone to help regulate traffic through it. As traffic builds to conditions where waves are likely to form, controllers set speed limits to regulate traffic flow at either 60mph or 50mph. This system, one of the most advanced in the world, uses real-time data collected from monitors on the carriageway and analysed by TRL experts to set strategic variable speed limits to try to alleviate problems before they materialise. ![]() TRL developed the traffic management system that controls the flow on the London orbital M25 motorway. Ideally, to alleviate this type of effect, drivers should stay on the inside lane for a mile or so after merging with motorway traffic – but that rarely happens." That leads to a ripple effect which can stretch back 20 miles. "When traffic merges vehicles have a tendency to cut across lanes moving into gaps in the traffic flow, causing drivers behind to slow or brake. "Any city serviced by motorways which merge as they approach it will be prone to congestion," he says. Thanks to its breakneck development, Beijing is now one of the top global traffic hotspots along with Sao Paolo, Mexico City, Johannesburg, New Delhi, Moscow, London, New York, Los Angeles and Tokyo.Īccording to Tim Rees, head of traffic behaviour at research and development consultancy Transport Research Laboratory (TRL), major city road layouts have a lot to answer for. Stranded drivers struggled to travel two miles a day and the queue generated its own economy, with industrious hawkers selling provisions to motorists at vastly inflated prices. That monster jam was blamed on roadworks, a broken-down car and an overload of trucks carrying coal from Mongolia to the capital. The causes of some jams, such as the recent 100km queue in China, which snared drivers for days on the main north-south motorway to Beijing, are easily identified. Of course, scientific theory is not always needed to explain gridlock. Scientists studying the same phenomenon at MIT in the US discovered that "jamitons" share similar characteristics to the detonation waves created by explosions. These clusters, which scientists call "jamitons", spread backwards through the traffic like a shock wave. Initially the traffic moved freely, but small fluctuations soon appeared in distances between cars and built into larger pockets of congestion. Researchers in Japan observed a similar "wave" pattern when they put 22 vehicles on a 23-metre, single-lane circuit and asked drivers to cruise steadily at 30km an hour. More recently, a team of mathematicians from the University of Exeter discovered that these congestion waves were not due to sheer weight of traffic, but were down to driver action. This condition allowed waves of dense traffic to pass upstream along a motorway. He discovered that on carriageways where the traffic was moving in this manner vehicles appeared to have jelled into a type of unified, moving mass. ![]() The commonly held view was that these patterns were caused by sheer weight of traffic.īoris Kerner, a researcher working at the Daimler Chrysler Research Centre in Germany, studied the traffic state between freely flowing cars and a full-scale traffic jam, which he called "synchronised traffic flow". Other models found a similar effect, where vehicle flows turned suddenly sluggish and stopped, as if they had crystallised. Within the computer programme, virtual cars would organise themselves spontaneously into distinctive patterns. In the mid-Nineties, researchers in the US first built simulations which mirrored this effect. Although roads carrying vehicles at a certain density will always become congested, traffic scientists puzzled for years over those annoying jams that occur on free-flowing roads for no apparent reason. Today's jambusters arm themselves with powerful computer-simulation tools to construct virtual highways containing thousands of virtual vehicles which interact with each other and gives clues as to why seemingly random congestion occurs.
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