Every city is a system formed by certain sub-systems. Transportation and green systems are the sub-systems which form the cities and which have important effects on their formation period. The relation between these is the starting point of this study. The development of the transportation system brings a lot of problems along with the easiness it provides. The growth of the settlements and the damage to the natural environment are one of the most important problems that the transportation system brings. Its rapid and unsystematic growth has caused transportation problems in Istanbul. The ongoing development of the transportation system related to problem solving, has brought the Bosporus transition proposal along. Starting from the years 1967-1968, when the 1st bridge was on the order of the day and up until the 3rd bridge proposal, the analysis of the effects of the two bridges on the urban centers, urban expansion and natural green system of Istanbul, has formed the purpose of the study. During the study period, following the examination of the effects of the existing two bridges in the years of 1975, 1995 and 2005, the possible effects of the 3rd bridge route have been examined. The methods used in this study are Landsat, GIS. The Landsat satellite images of the years are examined and analysed by GIS, which is a system that collects, stores, processes, analyses and displays the earth referenced data. It can be said that there is an ongoing decrease in open space systems by the increase in the population and settlement areas since 1975. According to the results of this study, when the alternative 3rd bridge route is proposed, it is designated that there will be all increase of the settlements in Istanbul, mainly around this route. Therefore, the proposed 3rd bridge route will form a great threat on agricultural areas, forests, water and water collection areas which form the open space systems of Istanbul.