İki kara parçası arasında yer alan boğazlar, farklı iki noktadaki deniz geçişinin sağlanmasına izin verirken, aynı zamanda iki yaka arasındaki doğrudan geçişin de engellenmesine neden olmaktadırlar. Kesintisiz ulaşım amacıyla yapılması planlanan boğaz köprüleri, gerek yapım aşamasında, gerekse yapıldıktan sonra dışsal ekonomiler ortaya çıkarmaktadır. Boğaz köprüsü merkez nokta olarak kabul edildiğinde, kısa vadede yalnızca merkez ve dolayında, uzun vadede ise bağlantı yolları ve çevresinde ekonomik, sosyal ve çevresel olmak üzere çok boyutlu etkileri olmaktadır. Bu çalışmadaki amaç, Çanakkale’de yapılması planlanan boğaz köprüsünün ortaya çıkarabileceği dışsallıkların neler olabileceğini; yazın taraması, anket ve derinlemesine görüşmeler yoluyla belirleyerek, boğaz köprüsü projelerinde öngörülmesi gereken dışsal fayda ve maliyetlerin neler olabileceğini ortaya koymak olmuştur.

Straits located between two land pieces allow pass over sea from both sides and at the same time they also prevent direct pass for both sides from one to the other. Transportation based problem was solved by using sea transport for years. Gradually, with the improvement in knowledge, technology and engineering fields, bridges were built. Actually, bridges were the result of progress in human movements and demand stemming from fast and flawless transportation of the society. Bridges are built in the aim of establishing direct transportation from one side to another side of the rivers and bridges over straits form negative and positive externalities both during their construction and following their completion of structure. Because external economies are stated as economies that are formed as a result of the functioning of an economic unit and that cause benefit or costs to other economic units. Thus results of externality process also have effects on the third parties except for the buyer and seller. In other words, it implies the spread of negative or positive externatilities as a result of the production and consumption activities of a certain member of the society to other members of the society. This means that the loss can not be met while imposing a cost and special benefits can not be priced while it is obtained. However when the bridges are built, these externalities, which first affect center and its environment in the short term and then linking roads and their surroundings even in the surrounding cities in the long term, cause multi-dimensional effects towards economic, social and environmental fronts. While projections of external effects which can be forecasted are reflected to prepared reports, unprojected external effects could not be reflected. However, some of the projected and unprojected external costs and special benefits are reflected on the costs consiously or unconsiously during the bidding process. Because during the bidding process between the institution that bids the strait and that takes the job of construction margianl private benefit and costs are ignored. Generally, lowest costs that are feaseble to both parties are taken into consideration which means the ignorance of various economic, social, and environmental factors during the construction of the bridge. Therefore third parties which are not present during the bidding and construction process have to take positive and negative externalities. Some of the expected external positive effects of the bridge to be built accross the Dardanelles are facilitation of transportation, decreased levels of cost to pass from one side to the other side, time saving, increased levels of property prices, presentation of Dardanelles (will be well-known bridge for its size), contribution to GNP, contribution to tourism…etc. On the other hand some of the expected external negative effects of the bridge to be built accross the Dardanelles are its negative effects on the natural environment, increased levels of pollution, noise pollution, rent seeking effect, increased rates of traffic density, accident costs, unplanned urbanization…etc. Passes from one side to another in Canakkale is through the ferry transportation. Demand for fast and flawless transportation, time saving, and several other variables form the bases for the construction of a bridge. However, the bridge to be built will cause the occurance of several positive and negative externalities. The idea to construct a bridge in the Dardanelles was first came into mind in 1975 and the idea was seriously discussed during the following years and a bridge plan called “The Bridge of Ugur” was first prepared which included the plans of a possible bridge by the Mayor of the period, Orhan Ugur. The bridge’s project was prepared during the 1990s and it was taken into the state’s construction plans in 1994. However, following the political conflicts and early elections no concrete steps were taken. Years followed and only two projects have been prepared until 2012. In the second project that was prepared between 1994 to 2012, it was admitted that the first project only included the economic matters for the bridge and that positive and negative externalities might occur by the official units. Effects of bridges to be built over the straits are very complicated. Moreover, in the report it was stressed that the bridge to be built would have positive effects on the region and attempted to eliminate the negative externalities. Within the scope of the study, the study attempts to put forward that the costs during the construction of bridges in the Dardanelles, to be met just by the state or the company to build it, are not only the costs and that there are other costs caused by the externality of the situation in several dimensions. The bridges in the Bosphorus constitute good cases about positive and negative externalities. Because, the bridges in İstanbul caused some unexpected effects in time besides their ultimate purpose of establishing easy way of transportation. The first bridge “Boğaziçi Bridge”, which came into use in 1973, caused several negative and positive environmental and social effects. By the introduction of second bridge which came into use in 1988, similar effects particularly in the related destination and passages became clearer. Therefore, the study first conducts literature review and attempts to acknowledge theoretical views. For this purpose, secondary data about the positive and negative effects of bosphorus bridges built in Istanbul has been collected and compiled. The obtained secondary data also supported by a qalitative and quantitative research methods as complements to the study case. Opinions of interviewees about positive and negative externalities have been searched within the scope of in-depth interview. The interview included keywords that has been found by possible questions about the bridge planned to be built in Cannakkale regarding the positive and negative externalities. Three regions; Canakkale city center, Lapseki and Gallipoli also identified by the conducted survey, participants’ attitudes towards the bridge to be built in Canakkale have been measured and obtained data has been analysed by using multi-variable statistical analysis methods with respect to the purposes of the study. As a result of the literature review, in-depth interview and survey; positive and negative externalities of the bridge planned to be built in Canakkale and issues that would be faced about this project in the future have been put forward. Projections made in this study are not only valid for Canakkale province since they stem from the bridge to be built in Canakkale, but also they are valid for the bridges that would be constructed as third or even the fourth bridges in Bosphorus in the future.