Ten Questions & Answers About Traffic Jam

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  • Topic: Road, Traffic congestion, Road transport
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  • Published : October 30, 2012
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TEN QUESTIONS AND ANSWERS ABOUT TRAFFIC JAMS

January 2012

LISTENING TO THE TRAFFIC JAM INFORMATION IS NOT THE MOST PLEASURABLE MOMENT OF THE DAY FOR MANY. ISN’T IT TIME TO SOLVE ALL THOSE TRAFFIC JAMS? THAT’S PROBABLY NOT GOING TO HAPPEN. BUT WE CAN LOOK AT THINGS IN A DIFFERENT WAY. HOW CAN WE BOOST THE ACCESSIBILITY OF LOCATIONS AND THE RELIABILITY OF OUR TRAVEL INFORMATION? WHAT ALTERNATIVES CAN WE DEPLOY? OR, HOW CAN WE FACILITATE MOBILITY? TEN QUESTIONS AND ANSWERS ABOUT TNO AND TRAFFIC JAMS.

JRV090112-02

TEN QUESTIONS AND ANSWERS ABOUT TRAFFIC JAMS
1. What are traffic jams? In short, a traffic jam occurs when a number of road users cannot drive at the speed they would like to drive, up to the maximum speed. While road users have learned to live with this, and sometimes even regard delays as an opportunity to rest, traffic jams are still undesirable for a variety of reasons. Some undesired effect are a higher risk of collision due to unexpected braking, extra CO2 emissions due to constant slowing and accelerating, economic damage caused by goods being on the road longer or irritation among drivers who had not taken the extra travel time into account. The Traffic Information Department defines a traffic jam as a collective term for three types of stagnating traffic: − Slow-moving traffic: traffic that moves slower than 50 km/hr but faster than 25 km/hr over a distance of at least 2 km. − Stationary traffic: traffic that moves at less than 25 km/hr almost throughout but for at least 2 kilometres. − Slow-moving to stationary traffic: slow-moving traffic over a longer distance with ‘pockets’ of stationary traffic. 2. How do traffic jams arise? A traffic jam is a capacity problem. If the capacity needed – the number of road users who want to go from one place to another – exceeds the available capacity of, for instance, a section of road, the traffic flow is disrupted. As a result, there is too much demand (as during rush-hour), too little capacity (as in a closed-off lane) or a combination of the two. Capacity is not, however, a given. Car-to-car following distance depends on the weather, and the lane width has an effect on speed. In general, traffic flow is good most of the time but when it is busy, little is needed to tilt the balance: for example, merging traffic, a fog bank, someone braking, road works or a roadside breakdown. 3. What impact do traffic jams have? The severity of the disruption depends on the type of traffic jam. An incidental traffic jam, such as that resulting from an accident, can cause severe delays. But when the road is freed up, the traffic gets going again, often so quickly that the road user who did not see the accident wonders why he had not been moving. Changes to and within the infrastructure can also cause a traffic jam. These include a permanent bottleneck or temporary road works where traffic merges from three to two lanes. In these kinds of traffic jams, the road user can be fairly sure what he can expect by using the ANWB’s (Dutch Automobile Association) traffic jam predictor. A so-called shockwave traffic jam may occur at a merging lane where the through traffic brakes for merging traffic. The first road user that lets one vehicle merge only has to brake very slightly to set off a shockwave reaction. The road user some way behind then has to brake hard and the road user even further behind may even have to stop. If the queue ahead starts moving slowly and has to brake again, the whole cycle begins anew creating a shockwave. It is difficult to say exactly where the traffic jam starts and ends. 4. Can we solve traffic jams? Traffic jams are a by-product, a detrimental effect, even though they may not be experienced as a by-product. The fact is that people want to drive from A to B quickly, reliably and safely. If, for example, an extra lane is constructed, a few years later traffic jams occur again. But more people can travel from A to B, just as quickly if not more quickly....
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