Otoyollarda kullanılan geometrik ve fiziki standaertların irdelenmesi ve Türkiye'deki uygulamalar
Başlık çevirisi mevcut değil.
- Tez No: 55673
- Danışmanlar: PROF.DR. NADİR YAYLA
- Tez Türü: Yüksek Lisans
- Konular: İnşaat Mühendisliği, Civil Engineering
- Anahtar Kelimeler: Belirtilmemiş.
- Yıl: 1996
- Dil: Türkçe
- Üniversite: İstanbul Teknik Üniversitesi
- Enstitü: Fen Bilimleri Enstitüsü
- Ana Bilim Dalı: Belirtilmemiş.
- Bilim Dalı: Belirtilmemiş.
- Sayfa Sayısı: 155
Özet
ÖZET Yirminci yüzyılın ikinci yansından itibaren teknolojik alanda olağanüstü gelişmeler yaşanmaya başlamış ve bu gelişmeler sonucunda çeşitli tip ve ağırlıktaki araçların üretiminde önemli oranda artış sözkonusu olmuştur. Artan araç sayısı karşısında mevcut yol kapasitesi yetersiz kalmış ve daha ekonomik, emniyetli ve konforlu karayolu altyapısı gereksinimi doğmuştur. Ülkemiz tarih boyunca Avrupa ve Asya kıtaları arasındaki karayolu ulaşımında tercih edilen bir güzergah olmuş ve halen bu özelliği devam etmektedir. Ancak mevcut karayolu ağımızın belirli kesimleri artan trafik hacmi karşısında yetersiz kalmakta ve gereksinime yanıt verememektedir. Bu nedenle ülkemizde mevcut yollar muhafaza edilerek otoyolların yapımı önem kazanmaktadır. Bu çalışmamızda karayolu ulaşımında önem kazanan otoyolların fiziki ve geometrik standartları hakkında bilgi verilmekte ve ülkemizdeki otoyollar uluslararası standartlar çerçevesinde değerlendirilmektedir. Ayrıca çalışmamızda bütünsellik sağlamak açısından standartların yanısıra otoyolların diğer elemanlarına yer verilmiş ve sözkonusu elemanlar kavramsal olarak açıklanmıştır. Çalışmamızın birinci ve ikinci bölümlerinde otoyolların tarihçesi ve gelişimi hakkında bilgi verilmiştir. Üçüncü bölümde otoyolların geometrik ve fiziki standartlar açıklanmış, ayrıca üstyapı tipleri, yüzey özellikleri ve kalınlıkları hakkında bilgiler verilmiştir. Daha sonraki bölümlerde ise otoyollarda drenaj, peyzaj ve güvenlik elemanlarına yer verilmiştir. En son olarak da Türkiye'deki otoyollarda uygulanmakta olan standartlar çeşitli ülkelerdekilerle karşılaştırılmıştır. Tezimizin bu konuda yapılan çalışmalara ışık tutacağı inancındayız. viii
Özet (Çeviri)
SUMMARY INVESTIGATION OF THE GEOMETRIC AND PHSICAL STANDARDS WHICH ARE BEING USED ON MOTORWAYS, AND, APPLICATIONS IN TURKEY This work has covered the observation of the geometric and physical standards which are being used at motorways, and, conceptual explanations have been made for other auxiliary elements like drainage, landscaping, security elements. Besides examples regarding the applications in Turkey and in the world, have been given. Given the basic characteristic of drivers, vehicles and road, the highway designer is in the position to develop the geometries of individual roads. First a design speed and ruling grade must be determined after weighing such factors as the road's importance, the estimated amount and character of traffic, the terrain, and the availability of funds. Design speed and ruling grade in turn provide the basis, for setting minimum standards for vertical and horizontal alignment. Then the designer, to a large degree by trial and error, fits these or higher standards to the terrain as shown on arterial photographs, maps, and other exhibits to produce a plan and profile for the main roadway. Along with decisions concerning the continuous roadway, the designer also develops details of the geometry of intersections or interchanges, service roads, and similar features. Finally, particulars of signing, striping, traffic signals, if any, and other traffic control devices must be worked out. Possibly the most important single rule in highway design is consistency. Only by making, ever element conform to the driver's expectations and avoiding abrupt changes in standards can a smooth-flowing accident-free facility be produced. Experienced highway designers recommend that the signing for the highway be planned as an integral part of the preliminary layout studies. If directions to drivers can be planned to convey one simple message at a time, and if these directions can be followed smoothly, easily, and without undue haste or changes in speed, then the plans for the facility will be satisfactory. Publications of AASHTO (AASHO) which include A Policy on Geometric Design for Rural Highways, A Policy on Design of Urban Highways and Arterial Streets, and Design Standards for the Interstate System, Highways Other Than Freeways and for Local Roads and Streets are the standards of accepted practice in the United States. Revisions to these standards are made on occasion. Much of the material presented on this study is drawn from these sources. The Manual on Uniform Traffic Control Devices, published by the Federal Highway Administration, is authoritative as to signs, signals, and pavement markings. Among tihe chief advantages of these standards are the pooling of collective knowledge and experience and the nationwide uniformity and consistency that results.No single set of geometric standards will apply to all highways. To illustrate, it seems appropriate to design a mountain road that is primarily for passenger cars numbering 50 or fewer a day to the following standards: Minimum speed, 20 mph; maximum grade, %12; and total width of road and shoulders, 24 ft. At the other extreme, consider a major freeway on the Interstate System or other primary network which is to carry mixed traffic of 100.000 vehicles per day. Appropriate standards in this case could include: Design speed, 70 mph; maximum grade, %3; total width of roadway and shoulders including a median, 160 ft; and right-of-way width, including service roads, ranging from 250 to 500 ft. Standards for other facilities would fall between these extremes. For each highway segment, decisionsregarding appropriate controls for every one of the many details must be reached. Furthermore, there are a few“right”answers; for example, what constitutes“heavy”truck traffic which limits the maximum grade to %3, and why should this limit be %3 rather than %2.5 or %3.5? Again, why 4 to 1 side slopes rather than 3 to 1 or 6 to 1? In some instances, the commonly accepted standards are supported by research; in others they represent a pooling of the judgment of many competent engineers. Seldom, however, can they be considered as exact or beyond debate. The Trans European Motorway (TEM) project planned to facilitate efficient road travel across central and south-east Europe. In order to maximize the expected benefits to users a consistently high design standard should apply throughout the route. The selection of a particular design speed is influenced by many factors, notably the topography of the area and its effect on construction cost, vehicle operating costs and the environmental impact of the scheme. When in service the operational speed of any road is further influenced by the“level of service”prevailing on it; in particular, vehicular interaction, especially at interchanges, can reduce the speed of traffic below the desired level of service. A design speed of 120 kph has been adopted for the Trans European Motorway. This reflects common practice for inter-regional strategic highways throught Europe and is an estimate of the speed that traffic is likely to adopt on the proposed alignment. Associated with the design speed is a set of minimum criteria describing the geometric features of the highway. These attempt to reduce the number of potential hazards presented to drivers and thereby lower both the anticipated accident rate of the road and the cost of traveling along it. Design speed is defined in AASHO Highway Definitions as“A speed determined for design and correlation of the physical features of a highway that influence vehicle operation. It is the maximum safe speed that can be maintained over a specified section of highway when conditions are so favorable that the design features of the highway govern.”AASHO recommends that design speeds be set to the greatest degree possible to satisfy the needs of nearly all drivers both today and throughout the road's anticipated life. Selection of the proper design speed is extremely important, because this choice sets the limits for curvature, sight distance, and other geometric features. Since available xfunds are often limited, there is the temptation to reduce design speeds in order to save money. However, to do so may be unwise. When economy is necessary, it should be practiced on other features then the geometric ones. The roadway section can always be improved and widened. The paving surface can be widened and strengthened at any fixture day that finances will permit. But the geometric features of alignment, grade, and sight distance, when once molded into the landscape and tied down with paving surfaces and rights of way, are most difficult and expensive to correct. Table.3.2 gives a comparison between the standards proposed for K.G.M. and the equivalent national standards from Great Britain, United States, West Germany and Italy. Current UK practice utilizes a hierarchy of geometric design criteria related to design speed. This may be termed desirable, absolute and limiting standards. Such a system permits a degree of flexibility in the application of standards in a range of situations, where the strict adherence to a particular standard would lead to disproportionately high construction costs or severe environmental impact on people, property and landscape.“Desirable”minimum radii produce a high standard of road safety and are the design objective. Relaxation to“absolute”can be fully justified and provide a satisfactory level of service with almost undetectable erosion of safety, in order to overcome alignment difficulties or to achieve significant savings in cost or environmental terms. The alignment of a road is shown on the plan view and is a series of straight lines called tangents connected by circular curves. In modern practice it is common to interpose transition or spiral curves between tangents and circular curves. Alignment must be consistent. Sudden changes from flat to sharp curves and long tangents followed by sharp curves must be avoided; otherwise accident hazards will be created. Likewise, placing circular curves of different radii end to end (compound curves) or having a short tangents between two curves is poor practice unless suitable transitions between them are provided. Long, flat curves are preferable at all times, as they are pleasing in appearance and decrease the possibility of future obsolescence. A vehicle traveling in a curved path is subject to centrifugal force. This is balanced by an equal and opposite force developedthrough superelevation and side friction. From a highway design standpoint, neither superelevation nor side friction can exceed certain maximums, and these controls place limits on the sharpness of curve that can be used with a prescribed design speed. For curves flatter than those specified by Table.3.3 for a given design speed, the engineer must choose whether, in a given situation, it is better to reduce side friction, superelevation, or both. Suppose, for example, there is a good reason to discourage travel faster than design speed. Then, on flatter curves along the road, superelevation could be set to develop side friction to its maximum permissible value. On the other hand, it might be desirable to miriimize side friction by using full superelevation. Even for high-speed designs, vehicle traveling around flat curves develop relatively little centrifugal force. This can be compensated by a small amount of superelevation. XITransitions in the form of clothoid spirals are to be included between horizontal curves or straights. They are not required on radii greater than a specific radius, when dynamic criteria become negligible. For aesthetic reasons, transitions consuming approximately 3 degrees are preferred. In order to achieve this requirement, for radii in excess of 3 A (A is clothoid parameter), a transition length equal to R/9 (R is radius) is required. Where transition curves are provided, changes in superelevation will usually be applied over the full length of the transition curve, or such that the difference in grade between the inner ant outer edges of the carriageway does not exceed %0.5, whichever is the longer. This will be applied such that 2/3 of the total length of application is on the straight, and the remaining 1/3 is on the curve. In all cases superelevation will be applied in such a way as to ensure that surface water drainage flat spots are either not created or reduced to an absolute minimum length. The design standard of the vertical alignment directly affects the construction cost because of its influence on earthworks quantities and the vehicle operating cost, which increases rapidly on steep up-gradients. UK recommendations suggest that on motorways, gradients excess of %4 will be regarded as a departure from standards; elsewhere gradients of up to %8 considered justified if significant saving in construction or environmental costs can be made. Above %8 a progressive decrease in safety is likely to result. On high speed roads, including motorways, the principal criteria governing vertical curves between straight grades are visibility over crests and comfort in sags, where visibility is not obscured by the road ahead. Parabolic curves are preferred since they provide a constant rate of change of curvature. The grade line is shown on a profile taken along the road centerline and is a series of straight lines connected by parabolic vertical curves to which the straight grades are tangent. In laying this grade line, the designer must secure economy by keeping earthwork quantities to the minimum consistent with meeting sight distance and other design requirements. In mountainous country the grade may be set to balance excavation against embankment as a clue toward least overall cost. In flat or prairie country it will be approximately parallel to the ground surface but sufficiently above it to allow surface drainage and, where necessary, to permit the wing to clear drifting snow. Where the road approaches or follows along streams, the height of the grade line may be dictated by the expected level of flood waters. Under all conditions, smooth flowing grade lines are preferable to choppy ones of many short straight sections connected with short vertical curves. With divided highways having separate grade lines in the two directions, alignment and grades must be coordinates to prevent headlights from vehicles going in one direction from blinding the drivers of vehicles going in the other. Maximum grades for the several highway systems as set by AASHO, are given in Table.3.5. Standards setting minimum grades are of importance only when surface drainage is a problem, as when water must be carried away in a gutter or roadside ditch. In such instances AASHO suggests a minimum of %0.5, but this may be reduced to 0.35 % with a high type of pavement. xiiIn meeting on coming vehicles or passing slower ones, the position selected by a driver depends primarily on the paved or surfaced width of the highway. Today, 12 ft lanes are regarded as necessary for freeways and other major traffic arterials. For two lane rural highways, 24 ft wide surfacing are standard for design-hour volumes greater than 400 vehicles. Minimum surfacing widths of 20 or 22 ft are considered appropriate for lower volumes at lower speeds. AASHO polish recognizes a roadway 16 lanes wide consisting of four lanes in each direction in an inner freeway with four more freeway lanes in each direction on the outside. The shoulder is that portion of the roadway between the outer edge of the traffic lane and the inside edge of the ditch, gutter, curb, or slope. Divided highways also may have an inside shoulder between the inside lane and the median. Shoulders provide a place for vehicles to park when disabled or when stopped for any other reason. If design omit shoulders, or if they are narrow, roadway capacity decreases and accident opportunity may increase. AASHO recommendations are in terms of the“usable shoulder”width, or that which can be employed for emergency stops. Where inslopes or side slopes are 4 to 1 or flatter, usable shoulder width equals nominal shoulder width, which is the distance from pavement edge to the intersection of shoulder and side slope planes. Usable shoulder width on slopes steeper than 4 to 1 is defined as ending at the point where rounding to inslope or side slope begins. Positive separation between opposing streams of traffic has proved to be an effective means for reducing headlight glare, conflicts, and accidents on multilane highways. Today medians in some form are an absolute requirement for all freeways. Wide medians are to be preferred wherever space and cost considerations permit. For rural sections of the Interstate System in flat or rolling topography, minimum width is set at 36 ft. However, medians up to several hundred feet have been provided in some instances, thereby completely isolating one roadway from the noise, confusion, and headlight glare of the other. There is a growing use of separate alignments and grade lines for the two roadways, with wide medians of variable width and conformation. A climbing lane justified on this basis would be introduced as an extra 3.75 m (or 3.50 m) lane width a full width hardshoulder retained on the outside. This solution is preferred to utilizing the hardshoulder as a climbing lane since it is at precisely these locations that the hardshoulder is more likely to be required to park broken down vehicles and contain accident debris. Climbing lanes should become necessary to utilize the maximum permissible gradient of %4 for a distance greater than 500 m., the provision of a climbing lane will be considered on the basis of the criteria set out in the AASHTO Policy on Geometric Design of Highways and Streets 1984. In the past, cut or fill slope were standard for many highway agencies because they involved a minimum of earthwork. In recent years, however, slopes generally have been flattened to provide for safer operation, to facilite plant growth and reduce erosion, and to decrease maintenance costs. Steep slopes on fills create a serious accident hazard, also steep slopes on gutter ditches create similar accident hazards. AASHO standards now demand flat inslopes on the roadway side of such ditches and at the top of fill slopes. Flat fill slopes have the added advantage that they are visible from the vehicle for their full extent so that the road takes on a safer appearance. xuiEven though relatively steep slopes in earth will stand, they erode badly, thus creating serious environmental and maintenance problems. Furthermore, it is difficult to grow plants or grasses on them to aid in erosion control. Thus the saving in original excavation and embankment costs may be more than offset by increased maintenance through the years; and in addition the slopes will be unsightly. A Policy on Urban Highways and Arterial Streets recommends for flat or rolling country that 6 to 1 slopes be used on embankments less than 4 ft high and 4 to 1 slopes on higher fills. Only at heights greater than 20 ft would 2 to 1 slopes permitted. Standards are somewhat less severe in moderately steep or steep terrain. Cut slopes are never steeper than 2 to 1 except in solid rock or special soils. AASHO policies, as they apply to other major highways, are less stringent and permit steeper inclinations. In all instances, it is stipulated that where cut or fill slopes intersect the original ground surface, the cross section is to be rounded to blend the slope into the natural ground surface. On the outside of sharper curves or where side slopes are relatively high and steeper than 4 to 6 to 1, it is common practice to install guardrail. Its purpose is to keep the vehicle from leaving the roadbed, so that it will not overturn or strike a roadside object. Similar installations often are placed in front of bridge piers and abutments, sign or lighting supports, or trees or utility poles close by the roadside. As with median barriers, a variety of designs and materials have been employed. Recommended right-of-way widths for rural Interstate and urban freeways at grade are given in Table.3.9. For highways other than freeways and for streets, no specific right-of-way widths are indicated. It is recommended, however, that the acquisition be wide enough to accommodate all necessary elements, including appurtenances such as ramps, walls, and border areas. With increasing attention to screening major arteries from adjacent property for noise control or aesthetic reasons, added width may be required for planting or sound barriers. Fencing serves to prevent unwanted intrusion of animals, people, vehicles, or machines onto the highway. For high-speed, limited-access facilities in urban and suburban areas, positive means must be taken to ensure that pedestrians cross only at grade separations or other arranged and protected placed. Fences for this purpose are really to protect people from their own folly, for many prefer to face the hazard of crossing several lanes of fast-moving traffic rather than walk a short distance or climb a ramp or stairway. This work has also covered the explanations regarding the subjects of drainage, landscaping, traffic marking, for provision of totality with the subjects which have been mentioned above. In the last section, examples regarding the geometric and physical standards which are being applied at the motorways in Turkey, are given. xiv
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