Study On Method Based On Dial’s Algorithm For Multi-time Dynamic Traffic Assignment

The urban city has played a very important role in human’s living, social activities,business operation, material feeding and leisure entertainment, while traffic is treated as foundation of whole city operation. And as one of necessary premises in the development of society, urban traffic influences every field in our life.The United Nations Population Fund(UNPF) delivers a report in 2007 that the world is experiencing an unprecedented urbanization and developing countries and areas are even more so. And in 30 years of the early twenty-first century, it is estimated that the whole population of city in Asia will grow by more than double; in Africa area, it is about one point five times. In 2008, allegedly, the whole population around the world has exceeded total population in rural area, that is to say there will be more than half living in the city.China is quickly experiencing an urbanization, where 18 million annual rural populations get into the city. Although urbanization rate currently accounts for only 40%, at current peace,the urbanization rate in future will exceed more than 55% and it will account for 75% by2050. There will be tens of millions of rural population getting into the city. China has more than 660 cities, in the near future more than half of population will be the urban resident and there will be 83 cities which have more than 7.5 million population.One can not live without commutation in our daily life. Generally, with the increase of population, traffic demand will go up as well, particularly in the urban areas. And with continuous development of society and improvement of people’s livelihood, owning a private car has become a universal phenomenon. The burgeoning developments of automobile retail industry are also accompanied by the phenomenon, which gives rise to an increasing number of private cars. Meanwhile, measures such as road expansion and traffic capacity increasing can not keep up with the pace of traffic demand. Then conflict between traffic demand and supply inevitably appeared, which leads to social issues such as traffic accident,traffic delay and environmental issues. Traffic congestion, which is treated as origin of problems, is a big trouble not only in developing countries but also in those developed ones. And with deterioration of urban traffic congestion and traffic disorder, it has had a huge negative effect on the modern city construction and development of economy.For some, due to the far distance between living area and working area, people are widely in favor of the idea of using private cars as a way of commutation. The resultant traffic volume increasing compounds traffic congestion and intensified traffic accidents. In Tokyo,the length of road having traffic congestion degree more than 1.0 accounts more than half oftotal length, where links having degree more than 1.5 accounts more than 16%. Traffic congestion caused serious effects in economy, society and environment fields, including fuel waste produced by delay and low velocity and environment contamination generated by frequent firing-accelerating-braking. What’s more, because of congestion, aggressive or angry behavior by a driver of an automobile or other motor vehicle may occurred, and it is easy to induce accidents and serious impacts on quality of people’s life and even lead to economic depression, to some extent. The Texas Transportation Institute estimats that, in2000, the 75 largest metropolitan areas experienced 3.6 billion vehicle-hours of delay,resulting in 5.7 billion U.S. gallons(21.6 billion liters) in wasted fuel and $67.5 billion in lost productivity, or about 0.7% of the nation’s GDP. It is also estimated that the annual cost of congestion for each driver was approximately $1,000 in very large cities and $200 in small cities. Traffic congestion is increasing in major cities and delays are becoming more frequent in smaller cities and rural areas.Due to the traffic jam, the per capita commuting time increased by 1.5 hours, which causes vehicle delays during the commutation, increasing the cost of transportation and leading to substantial growth of economic loss year by year. The whole European countries attains economic loss over 500 billion Euros just in problems caused by traffic congestion. In Beijing,an annual investment of more than ￥100 billion for road network expansion still unable to cope with the increasing traffic volume.The annual vehicle-hour in America increases rapidly in the end of 20 th century, while a dramatic contrast with the increase is that there has few investments in planning about road construction, which leads to almost half of vehicles traveling on part of urban road network fall into congestion in rush hour. The August 2010 China National Highway 110 traffic jam in Hebei province, China, is considered the world’s worst traffic jam ever, as traffic congestion stretched more than 100 kilometers from August 14 to the 26. The event was caused by a combination of road works and thousands of coal trucks from Inner Mongolia’s coalfields that travel daily to Beijing. The New York Times has called this event the "Great Chinese Gridlock of 2010." In Beijing, number of links in congestion has been increased from 60 to80 currently. Towards the end of 2010, Beijing announced a series of drastic measures to tackle the city’s traffic jam, including limiting the number of new plates issued to passenger cars to 20,000 a month and barring cars of non-Beijing plates from entering areas within the Fifth Ring Road during rush hours.Although countries at home and abroad propose variety of methods in developing urban traffic to improve its efficiency of traffic and transportation, traffic jams are still regarded as ahard stone remaining to be crushed. Therefore, studies on traffic congestion have achieved more and more attentions from governments. Urban traffic, which is widely treated as the operation power of whole city, has a significant impact on development of economy and people’s livelihood. And because of this, it also attracts much attention from scholars who are devoted to solve traffic congestion. Hitherto, however, it remains a long way to crush such a hard stone. For decades, frequent incidents of traffic jams or road congestion obsess cities around the world, and it is of overriding urgency to solve traffic congestion.Researches on traffic problems in China, comparing with foreign countries, get started relatively low and its infrastructure of traffic and transportation is underdeveloped as well. In this way, traffic problem will get fierce with the rapid economic growth, and development of city and travel volume growth can also present a very serious challenge to the public traffic supply. The trend of urbanization and economic progress, especially in some large and medium scale cities, may render a dramatically increased traffic demand, which causes congestion phenomena everywhere in major cities and derives issues such as low traffic safety and urban pollution. In the face of short supply, China carries out huge investments.And at beginning of 21 st century, the total mileage of domestic highway has reached to65000 kilometers and the average annual incremental volume keeps at 5000 kilometers, but still congestion occurs in part of links and becomes more and more serious. In China, the total length of current domestic urban road is 0.26 million kilometers and area of city road is48200 square kilometers, while road area per capita has only 12.83 square meters, increase by2.8%, 6.54% and 0.62% respectively compared to the same period last year. The peace of transformation of road construction can not keep up with growth of vehicle traveling demand.Thus congestion problems in large and medium scale cities are getting more and more serious.With the improvement of equality in people’s daily life, urban travelers are not just content to reach to the destination any more. Instead, they have higher requirements such as safety and comfort in the course of traveling. Fast and comfortable transportation has become an indispensable aspect in traffic and transportation. That is to say, travelers’ examining and considering level of service has been upgraded from traffic facilities to high quality of experience(to reach to destination safely and comfortably). And then traffic jams are extremely intolerable for urban travelers.Because of backward road transport facilities compared to foreign countries and the improvement of people’s livelihood in recent years, ownership of private car continues to grow, and road facilities construction increased at a slowing down speed. This seems like thattraffic congestion is caused by mismatching between traffic demand and infrastructure supply and then quality of travel is reduced. But even if the level of domestic road facilities has been reached to developed countries, it is of little avail to solve shortness of urban traffic supply.Instead, what is worse is that arbitrary investments in infrastructure will attract much more demands just like what has happened developed countries like America. In addition, city road congestion will be deteriorated due to factors in traffic organization, which also directly caused frequent traffic accidents.Part of reasons causing traffic congestion stem from factors about traffic infrastructures,including unreasonable layout and structure of road network in the course of urban traffic planning, improper configuration, insufficient number of traffic facilities, the biased traffic demand overloading traffic supply capacity in part of regions, unreasonable traffic structure caused by the lack of measures conforming to the traffic control and heterogeneous distribution of traffic demand which leads to waste of traffic resources and may makes high cost link never be fully used. A general idea considers that improving efficiency and capacity of urban road network could solve traffic congestion problems. No matter what kinds of city it is, however, unlimited expansions and constructions in road network are unrealistic: First of all, limited resources ought to be taken into consideration. The second factor is that the objective terrain elements may makes it difficult to set up new traffic facilities in the city.Thirdly, the planning of urban road network is one of long-term programming, which belongs to measures that adapt to long-term strategies of traffic demand and cannot alleviate temporary serious congestion problems instantaneously. The comprehensive management of traffic flow and effective control, in comparison, could not only achieve good effect in deal with traffic congestion but also make timely adjustments according to the real dynamic traffic.And no matter in management of traffic demand or in analysis, it can optimize traffic flow and get effective traffic management.In order to improve the traffic capacity in the whole highway network, some measures can be taken, including expanding new roads, setting new overpass and reforming road network.While to make full use of traffic facilities, it is necessary to rely on relevant theoretical knowledge of traffic flow. After years of studies, achievements in the application about traffic control technology are finally acquired. Meanwhile, with the huge increase of domestic vehicle using in recent years, congestion situations in domestic city are still serious, which generally presents high frequency, long duration and big spread tendency of over saturated gridlock. Unfortunately, there are some defects in previous researches solving the situation,and this happens to highlight importance of studies on traffic assignment and planning.The total length of road built in China by the early 21 st century has come in second in the world, while from the national perspective, and phenomena of traffic jams are still common.The standard response to congestion is to expand road space somehow, perhaps by widening an existing road or else by adding a new road, bridge or tunnel. However, this could well result in increased traffic flow, causing congestion to appear somewhere else. Moreover,Braess’ s paradox shows that adding road capacity might make congestion worse even if demand does not increase. Thus various quantitative methods are used to deal with traffic problems. Moreover the Wardrop principle and the four stage method are the basic knowledge in studies of traffic problem, and the later is widely used because of its important role in traffic evaluation. As an outstanding part in the four stage method, traffic assignment distributes data acquired in other stages into the road network and then it get the forecast of traffic volume in the network, which could be the main reference for traffic planners and could to some extent impact the planning decision.It is very difficult to solve problems of traffic congestion just by traditional methods. In perspective of correlation, there are some relations amoung them, which are essentially reflected by the severe difference between expect of high level of traffic service cherished by travelers and the cruel reality in macro scope. If problems of traffic congestion are solved only in one aspect, it may results in other problems and worsens them. Because of large scale and complexity of urban traffic network, it is necessary to regard it as a systemized problem and solve it in a whole angle. In order to deal with traffic congestion problems in urban network, some of rules ought to be clarified, which requires knowledge and methods like cross class principles. For years of intelligent information process, only getting the new theoretical knowledge and sill about traffic planning and programming can one better solve the congestion problems. The intelligent transport system(ITS) proposed in USA in the end of last century has been the emblem of solutions in the background of information age.The Intelligent Transportation System(ITS), which belongs to advanced transportation system, are wildly developed and spread in countries over the world to apply the technology to transportation network according their own situation. While as core theory of Intelligent Transportation System, traffic assignment also plays a key role in the traffic guidance control system, which undoubtedly provides a solid platform for the combination of different intelligent traffic technology.Because of large scale and complexity of urban road network, in the process of researches,it is necessary to employ knowledge of system engineering. In the course of taking programming measures, planners in traffic and transportation field ought to make decisionswith systemic thoughts, taking public traffic system factors such as travelers, vehicles and roads into consideration and combining relative techniques with those factors to get a high-integrated urban traffic road network. The intelligent transport system is born in such a background, which comprises advanced traffic management systems, advanced traveler information systems, advanced vehicle control system and advanced public transportation systems.The intelligent transport system, currently, comprises technologies like communication,automatic controlling, built-in image processing and hardware developing. In default of network model and algorithm about computer program in the field of dynamic traffic, the intelligent management in large scale network encounters challenges. This results from artificial researches about analyzing behavior and characteristics in complex dynamic traffic network. And because of this, traffic assignment of urban network which plays an important role in the techniques attracts much attention from scholars at home and abroad. Due to defections of models and algorithms in solving traffic assignment of large scale urban network, there are some differences between theoretical depiction and actual case. It has many researches on travel path choice under different traffic conditions, in the act of study of dynamic traffic network, but discussions about basic travel model and whether the model can apply to the real case remain in destitution. This includes whether the impedance of road can reflect traffic conditions in real case, which inevitably impacts assignment results and plays crucial roles in providing decision maker with references. Moreover, the defection confines development of dynamic traffic assignment both in theory and application field.In the aspect of intelligent transportation, systems of real-time signal controlling and traffic guidance are jointly undertaken management of online traffic system. Because of difference in management between the real-time signal controlling system and traffic guidance system,they are designed respectively at the early stage. As a matter of fact, integrating the two systems together effectively can achieve good effect in releasing urban traffic congestion. In macro sense, the systems are inseparable both in theory and practice, so it does make sense to combine them together. And this makes combination of real-time signal controlling system and traffic guidance system becomes a branch of study on transportation planning and management and becomes a hot topic attracting thousands of scholars. But it is also based on the dynamic traffic assignment.The macroscopic traffic flow has been regarded as important part in theory of traffic flow system. With the increasingly prominent problems in urban traffic, the demand for traffic flow theory in traffic science becomes more and more urgent. The continuous type ofdynamic traffic assignment(DTA) is the combination of road traffic flow and network traffic flow. Nowadays, in fields of guidance technology, its theoretical basis is mainly used to analyze and reflect characteristics of macro traffic in the large scale traffic network system.Because the static traffic assignment can not perfectly reflect status of traffic congestion in actual case and the model of dynamic traffic assignment may cause a huge computation cost,the article combines features of static traffic assignment and the dynamic one and has Dial’s algorithm based multi-time dynamic assignment to get a balance between precision of description and computation cost. According to the method in the article, corresponding heuristic procedure is proposed, and it is also examined by numerical example of traffic assignment in situation such as network with different linear and nonlinear traveling function,network with link capacity constraint, one origin one destination and one origin several destinations OD pair paradigm. And it also proposes fitting function proximately reflecting overloaded condition in BPR paradigm and compares assignment results of BPR function with methods from other studies to prove practicality and correctness of multi-time assignment based on Dial’s theory in the article.