If you've ever driven on a highway, you've probably seen it happen. Traffic slows to a crawl, then stops entirely. Minutes later, it begins to move again, and then suddenly, you're moving at full speed. The weirdest part: there's no construction, accident, or other possible explanation for the traffic. Why does this happen? As it turns out, a few different groups of researchers have been using mathematical calculations and real-world experiments to try answering this question.
And they think they have the answer. They also have suggestions on how to stop these jams. If there are enough cars on a highway, any minor disruptions to the flow of traffic can cause a self-reinforcing chain reaction: one car brakes slightly, and the ones behind it brake just a bit more to avoid hitting it, with the braking eventually amplifying until it produces a wave of stopped or slowed traffic.
Even when cars leave this traffic wave, though, the wave itself doesn't disappear: it gradually drifts backward, against the direction of traffic. He and others developed the concept of these waves which they call jamitons, because they're analogous to waves in physics called solitons using computer algorithms that simulate driving behavior:. Japanese researchers have also conducted real-world experiments that come to the same conclusion.
In one, they instructed 22 drivers to drive at the same speed Inevitably, traffic waves formed:. They can be supported by speed enforcement systems that use camera images to identify speeding vehicles and drivers. For some legal jurisdictions the approved VMS may need to be authorised in legislation in order to be enforceable. Speed control is often associated with lane control because both measures generally use the same display equipment gantries and signs.
It can also be used for incident management or traffic control through work zones. A similar effect may be achieved through variable speed advisory signs, which do not have to be legislatively enabled or enforced, although such signs may have lower levels of compliance.
Motorists may claim confusion over the mixture of regulatory fixed and advisory VMS speeds. The success of VSL requires that drivers understand, and comply with, the reasons behind changing the speed limit and the associated benefits.
In most cases, the displayed speed limit should match the conditions that drivers encounter. There will be some cases when circumstances call for a reduced speed limit for which the reason is not obvious — for example environmental reasons, or problems downstream such as incidents or work zones. In some systems for example, in UK on the motorway around London and Birmingham , the variable speed limit display is coupled with an automated enforcement system involving video cameras recording licence plate numbers , which issues citations to motorists exceeding the speed limit by a predetermined threshold.
Dowling R. G and Elias A. Highway Traffic Management A number of different control methods are applied on regional networks of motorways, freeways, expressways and other arterial roads. The methods include: monitoring arterial performance See Monitoring Activities dynamic signal control special plans, signal priority, queue by-pass dynamic geometric controls reversible lanes, dynamic turn prohibitions, dynamic turn lanes dynamic speed control with enforcement See Speed Management traveller information See Travel Information Systems Roadside Signals Regional traffic control and management systems most commonly communicate with drivers via VMS.
Multimedia: Smart Motorways - Red X means a lane is closed. This is achieved by: regulating the flow of additional traffic onto the motorway that, if unchecked, would trigger flow breakdown and lead to critical shockwaves monitoring and managing the merging traffic to achieve an even distribution and avoid large platoons of vehicles entering the motorway at once, which increases the risk of flow breakdown Ramp metering is implemented by installing traffic signals on the on-ramps to regulate the flow of traffic joining the motorway during peak or congested periods.
The system requires: control signals which can be two-light or three-light located towards the end of the access ramp before the main carriageway, activated during peak periods signs informing users of activation — or impending activation — of the ramp meter a traffic monitoring system automated with several sensors to determine current traffic flows on the main carriageway and traffic demand on the access ramp holding capacity on the access ramp to ensure that vehicle queues do not disrupt traffic on the surrounding arterial road network In practice, ramp metering systems are located upstream of recurrent bottleneck congestion points — and have a safety role in addition to relieving main-line congestion.
Work Zones Narrow lanes, hard shoulder running and contra-flow systems often operate during construction, maintenance, widening and reconstruction of motorways. Its objectives are to: monitor and manage the HGV traffic flow on the highway network improve journey times for light vehicles improve safety by reducing vehicle queues caused by slow lorries overtaking ensure a better acceptance of heavy goods vehicles by the other road users. Reversible lanes Having reversible, tidal flow or contraflow lanes on a motorway — or having an entirely separate, reversible roadway — permits otherwise unused capacity in the off-peak direction to be used in the peak direction of flow.
Movable median barriers To add capacity during peak periods, moveable barriers can be deployed. It works: in heavy but smooth traffic flows, by imposing or recommending a driving speed equal to the average speed of traffic during periods of heavy congestion, by imposing progressively slower speeds to gradually slow vehicles on the approach to a traffic jam area Apart from handling recurring periods of congestion, speed regulation is a tool that can be used in all traffic conditions to gradually slow vehicles approaching a traffic incident or accident area.
See Enforcement The major benefits of speed control are improved safety and better journey times. This measure requires: consistent and sufficiently dense traffic monitoring and data gathering flow rates, vehicle speeds and lane occupancy rates a high-performance algorithm to detect the onset of unstable traffic flows variable message signs at intervals allowing a continuous visibility of the signs for drivers consistent information initiatives local information campaign to explain the operation, periodic reminders of instructions Traffic monitoring is indispensable: the operation can be fully automated but an operator must be able to recover control at any time if an unexpected event occurs — such as an accident or sudden deterioration in weather conditions.
Multimedia: Smart motorways use technology to manage congestion. Reference sources. Case studies All case studies for this subject. Reference sources All links and references for this subject. Multimedia kit Videos 5 Tables 0 Documents 0 Pictures 1. Give us your feedback. Title Mr. Every driver has experienced "phantom" traffic jams, in which dense traffic crawls to a halt for no apparent reason.
Now, new research may have come up with a solution for this frustrating traffic pattern: maintaining equal spacing between cars on the road, rather than tailgating. Horn said phantom traffic jams are an emergent property of the flow of vehicles down a highway.
A phantom jam begins when a car in dense traffic slows down even slightly, which causes the car behind that vehicle to slow even more — and the slowing action spreads backward through the lane of traffic like a wave, getting worse the farther it spreads. Eventually, the cars far behind are forced to stop completely or risk hitting the slower vehicles ahead —and so the traffic grinds to a halt over nothing, Horn said. Horn has been working on the problem of phantom traffic jams for years, and he has come up with a solution: By splitting the difference between the cars in front and the cars behind, the spacing of cars in a stream of traffic can act as a damper on phantom traffic jams.
That is, it can prevent the slow-down effect from being amplified by the cars that follow behind, he said. Even if a different route takes five, 10 or even 20 minutes longer during normal traffic, it may save you 30 minutes or more during rush hour, while helping you to avoid dangerously busy intersections and roadways that are often what cause car crashes.
Many commuters swear by the free app Waze , which offers real-time traffic and road information. Although you have no control over construction zones or the weather, understanding what causes car crashes, which contribute to 25 percent of surprise traffic jams, can help you change your driving behavior and reduce accident claims.
When drivers use their phone to call or text while driving, their attention is diverted away from the road, which increases the likelihood of a crash. In fact, a recent study from the Virginia Tech Transportation Institute found that text messaging doubled the risk of a crash. Even tasks related to using the phone, such as reaching for it or looking for a contact, were associated with a greater crash risk.
So, what really causes car crashes? Even if you keep your phone off or out of reach, keep in mind that distracted driving also includes eating, drinking, smoking, grooming, looking at maps or a navigation system, and even talking to passengers.
If you have a young driver in your family, be sure to monitor their activities when driving and help educate them on the real dangers of what causes car crashes. Take the pledge with us! Download and print your certificate and promise to stop driving distracted. In , driving while under the influence of alcohol resulted in the deaths of 10, people—29 percent of the vehicle crash deaths that year.
Driving while tired can endanger you and the others on the road, too. In , there were fatalities related to drowsy driving. The number of fatalities and of drowsy-driving crashes overall has remained largely consistent across the past decade according to the National Highway Traffic Safety Administration.
Note that alcohol, prescription drugs, and even over-the-counter medications can increase your drowsiness, which leads to poorer attention, decreased accuracy, slower reaction times, and impaired mental processing, judgment, and decision-making. Another source of traffic accidents, especially during high-traffic times and in high-traffic areas, is road rage.
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