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Eşdüzey kavşakların kapasite analizyöntemleri

Methods for capacity analysis of single-level intersections

  1. Tez No: 39553
  2. Yazar: MURAT AKAD
  3. Danışmanlar: PROF.DR. ERGUN GEDİZLİOĞLU
  4. Tez Türü: Yüksek Lisans
  5. Konular: İnşaat Mühendisliği, Civil Engineering
  6. Anahtar Kelimeler: Belirtilmemiş.
  7. Yıl: 1994
  8. Dil: Türkçe
  9. Üniversite: İstanbul Teknik Üniversitesi
  10. Enstitü: Fen Bilimleri Enstitüsü
  11. Ana Bilim Dalı: Belirtilmemiş.
  12. Bilim Dalı: Belirtilmemiş.
  13. Sayfa Sayısı: 97

Özet

ÖZET Sürekli artan ulaştırma gereksinimleri, gerek kentlerde gerekse kırsal bölgelerde yol ağlarının artmasına ve genişlemesine neden olmaktadır. Bunun sonucunda orta ya çıkan trafik akımlarının çatışmaları sorunu, bu çatışmaları en aza indirgemek amacıyla kavşakların düzenlenme sini zorunlu kılar. Doğal olarak eş düzey kavşaklarda akımların çatışmaları, ve bunun sonucu ortaya çıkan kaza olma olasılığı, trafiğin düzenli akışını sağlamak amacıyla çeşitli önlemler alınmasını gerektirir. Kavşak denetimi olarak adlandırılan bu yöntemler, akımların birbirlerine yol vererek kavşakta zamanı paylaşmalarına yol açar. Söz konusu paylaşımları düzenlemek amacıyla, çeşitli denetim biçimleri uygulanmaktadır. Bu çalışmada öncelikle kapasite kavramı tanımlanmış tır. Daha sonra kavşaklar ele alınmış, ve uygulanması gereken denetim biçimleri temelinde sınıflandırılmışlar dır. Yapılan sınıflandırma çerçevesinde tanımlanan kav şaklardan anayol-yanyol kavşakları, sinyalize kavşaklar ve yuvarlak ada kavşaklar irdelenmiştir. Her üç kavşak türü için de, günümüzde geçerliliğini koruyan kapasite analiz yöntemlerinden bazıları incelenmiştir. Daha sonra, her bir kavşak türü için incelenen analiz yöntemleri çeşitli açılardan karşılaştırılmış ve değerlendirilmiştir.

Özet (Çeviri)

METHODS FOR CAPACITY ANALYSIS OF SINGLE-LEVEL INTERSECTIONS SUMMARY The development of civilization throughout the his tory of mankind, and the increase of economical and so cial relations resulting from this development, has caused transportation needs to grow rapidly. The fast development of technology during the twentieth century provoked the problem. In order to meet the broad transportation require ments, the number of journeys continuously increase. Naturally, this means that vehicle traffic gets more con centrated every day. High traffic flows causes a vast expansion of urban and rural road networks. As a result of this expansion, different traffic flows conflict with each other. To avoid the hazards of these conflicts, in tersections are arranged. Intersections can be defined as the road sections or areas, which are used collectively in time or in space, in a pre-determined order by flows coming from different directions and going to different directions. When shared in time by different flows with an order, they are called s ingle- level intersections. On these type of in tersections, flows use the road on the same elevation in different periods of time. In this study, single-level intersections are evaluated. Conflicts of flows form the basis for the high risk of accidents at intersections. In order to reduce this risk, certain measures have to be taken. Intersection control, as these measures are called, works upon the principle of vehicles giving way to each other. This means that different flows share a particular period of time at an intersection. Naturally, certain rules must be established in order to obtain orderly flows. Apart from the problem of safety, the increase of flows using the intersections will bring about the prob lem of capacity. To obtain the least amount of delay to VIeach vehicle, and to operate the intersection as effec tive as possible, intersection control is necessary. The factors that have to be aforethought in deter mining the type of intersection to be built are invest ment and operating costs, necessary capacity, delays and safety. Aesthetic considerations are also accounted for. Undoubtedly, the most important of all these factors is capacity. Furthermore, capacity directly affects all of the factors stated above. The question of capacity has always been a matter of discussion in the field of traffic engineering. Differ ent studies up to date have given different definitions of capacity. Thus, different definitions of the concept of capacity can be met in literatures of different coun tries. Probably one of the most widely used sources, the A- merican Highway Capacity Manual, defines capacity as“the maximum hourly rate of vehicles or pedestrians that can pass through a uniform road section under prevailing road, traffic and control conditions”. As for all road sections, capacity must be defined for intersections, too. While doing that, it should be kept in mind that an intersection is a localized point in a road network. On this location, different flows con flict with each other. Thus, interaction between flows is very high. This interaction prevents the flows from displaying independent flow characteristics. It can be concluded that, unlike any other road section, flows are much more dependant on each other at intersections. One of the flows at an intersection, which can be named as the“critical flow”, carries more volume than the other flows. When this critical flow becomes satu rated, the total flow passing through the intersection can be considered as its capacity. Full capacity is reached when all of the flows at an intersection are sat urated. The capacity definitions given above, suppose ideal conditions, that is traffic can flow freely, without any disturbances. Since ideal conditions can never be reached, these values will always be theoretical. Thus, another definition, explaining actual conditions, must be made. In fact, the HCM definition given above coincides with the idea of practical capacity. Since practical capacity is dependant on traffic conditions, it will have a different value in different traffic conditions. Therefore, an intersection will not have a specific prac tical capacity. To make this concept meaningful, traffic conditions must be stated clearly. The concept of level Vllof service must be used in this respect. Practical capacity and level of service can be very useful in intersection design. Before an intersection is built, its geometrical characteristics can be determined according to the desired level of service it will func tion with. As stated above, an intersection can be defined as the road sections or areas, which are used collectively in time or in space, in a pre-determined order by flows coming from different directions and going to different directions. In order to reduce the accident risk, and to achieve an orderly flow, certain measures have to be tak en, which are called intersection control. Capacities of intersections are closely related to their geometric layouts and especially the type of con trol applied. As the flows entering the intersection in crease, a more developed type of control must be used. The most developed control mechanism is signal izat ion. Accordingly, s ingle- level intersections can be cate gorized by the type of control applied to them. As laws and practice certify, the main distinction of intersec tions in Turkey, is whether any type of control is ap plied to them or not. Uncontrolled intersections are those which are not signalized or controlled manually. They may either carry signs indicating the priorities of flows, or they may not have any signs at all. In this context, intersections can be categorized as follows: I. Uncontro 1 1 ed i ntersec t i ons A. Intersections without signs B. Priority intersections i. Major/minor intersections ii. Intersections with priority on the right iii. Intersections with priority on the right II. Signalized intersections III. Roundabouts Although often present, intersections without signs do not have any accordance with intersection design. They don't bear any indication to which flow the priority should be yielded. They should be avoided by designers, and signs should be put up as soon as possible. Geometry of the roads leading to the intersection and the geometry of the intersection itself may help the driver to decide on priorities. Certain measures must be taken to slow down the vehicles before they enter these type of intersections. Intersections bearing signs that indicate priorities are called priority intersections. The most common of Vlllthis type are major/minor intersections, on which the flows on the major road have priority over the minor road flows. Priorities in intersections other than major/minor ones, are arranged by laws. Higher levels of traffic control include signal iza- tion and roundabouts. Capacity of major /minor intersections have been a major field of study in traffic engineering since the 1950' s. The first remarkable model was put by J. C. Tan ner. Other noteworthy studies by Harders, Ashworth, Grabe, Lamm, Owens, Tomasson & Wright, Salter & Roebuck followed. Built upon these, more comprehensive models, which also consider impedance effects, have taken the place of these basic ones. Among the many empirical, analytical and simulation models, four methods of capacity analysis for major/minor intersections are discussed in this stud- y. These are the empirical British PICADY method, the a- nalytical American Highway Capacity Manual 1985 and Ger man methods, and the Polish simulation model. The British PICADY computer program was first devel oped in 1980; and it is widely used in Britain in design ing major/minor intersections. It is based upon empiri cal equations regarding different flows at an intersec tion. As it can be seen from these equations and as the results prove, in British conditions, the main parameters affecting the intersection capacity are major road width, the major road median width, sight distances, and the way lanes are used by the flows. The American Highway Capacity Manual adapted Har ders' and Jessen's models to the US conditions and added the concept of level of service. This method determines the minor road capacity through the critical gaps in the major road stream which the minor road vehicles can use. Later, the potential capacity is corrected by an imped ance factor. The Polish method determines the minor road poten tial capacity with the help of the flow it will conflict and the critical gaps in the major road stream. Like the HCM-85 method, the Polish method too, multiplies the po tential capacity by the necessary impedance factors to obtain the real capacity. The German method uses the critical gap and follow ing headway to calculate the minor road capacity. Simi lar to the two latter methods described above, this meth od too, multiplies the capacity with an impedance factor. It considers the ranks of the flows at a major/minor XXintersection comprehensively. HCM-85, German and Polish methods have much in com mon regarding the capacity factors used in the capacity calculations. Traffic factors have a more significant role in these three methods. The British method, on the other side, takes into account the geometric factors with much more detail than the other methods. The next type of intersection studied in this report is the signalized intersection. The first memorable cap acity analysis method for signalized intersections was produced by Webster. Given its final shape in 1966, this method formed a basis for all of the later studies made on this subject. The most originative development in this field was produced by R. Akçelik in the early eight ies as he proposed what is called the Australian signal i- zation method. Along with the two methods discussed above, Swedish and American HCM-85 methods are explained in this study. The capacity of a signalized intersection depends on the volumes and the saturation flows of the streams lead ing to the intersection, and on the ratio of the effec tive green period given to each flow. For each phase of the cycle, a critical movement is determined. Certain values of this movement is used in cycle time calcula tions. To find the best cycle time which would optimize many factors along with intersection capacity, is the main aim of the capacity analysis methods for signalized i nter sec t i ons. To certify the critical movements, British, Swedish and HCM-85 methods use a value called flow ratio; where as, the Australian method uses the green time ratio for the same target. This latter approach is more realistic, as green time is a limiting concept for each movement. Another subject on which these methods differ, is the concept of lost time in a cycle. British and Swedish methods consider the end lag in a cycle as lost time. Contradict i vely, Australian and HCM-85 methods name this lag as end gain. A main differentiation between the British and Aus tralian methods, is that the first one employs the con cept of“phase lost time”; while the latter utilizes“movement lost time”. Movement lost time helps under stand the relationship between the movement and phase characteristics, for it evaluates the lost times for each movement separately. Another developed type of intersection is the round about. Roundabouts are applied when the total flowintersection comprehensively. HCM-85, German and Polish methods have much in com mon regarding the capacity factors used in the capacity calculations. Traffic factors have a more significant role in these three methods. The British method, on the other side, takes into account the geometric factors with much more detail than the other methods. The next type of intersection studied in this report is the signalized intersection. The first memorable cap acity analysis method for signalized intersections was produced by Webster. Given its final shape in 1966, this method formed a basis for all of the later studies made on this subject. The most originative development in this field was produced by R. Akçelik in the early eight ies as he proposed what is called the Australian signal i- zation method. Along with the two methods discussed above, Swedish and American HCM-85 methods are explained in this study. The capacity of a signalized intersection depends on the volumes and the saturation flows of the streams lead ing to the intersection, and on the ratio of the effec tive green period given to each flow. For each phase of the cycle, a critical movement is determined. Certain values of this movement is used in cycle time calcula tions. To find the best cycle time which would optimize many factors along with intersection capacity, is the main aim of the capacity analysis methods for signalized i nter sec t i ons. To certify the critical movements, British, Swedish and HCM-85 methods use a value called flow ratio; where as, the Australian method uses the green time ratio for the same target. This latter approach is more realistic, as green time is a limiting concept for each movement. Another subject on which these methods differ, is the concept of lost time in a cycle. British and Swedish methods consider the end lag in a cycle as lost time. Contradict i vely, Australian and HCM-85 methods name this lag as end gain. A main differentiation between the British and Aus tralian methods, is that the first one employs the con cept of“phase lost time”; while the latter utilizes“movement lost time”. Movement lost time helps under stand the relationship between the movement and phase characteristics, for it evaluates the lost times for each movement separately. Another developed type of intersection is the round about. Roundabouts are applied when the total flow

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