The impact of urban tunnels on urban development and change: Istanbul experience

Istanbul is a city with a deep history rooted even beyond the Roman Empire. The characteristics of the present texture of the city are based on this historical past and its development is affected by this texture and develops as an extension of it. Istanbul is a city that especially takes immigration from the rural areas and the eastern regions of Turkey. Its population reached to 15 million with the immigration it has received. The potential that the increasing population brings and the demand that the vehicle ownership increasing each year with the current urban transport pattern have caused a great traffic density problem in the city. The urban people who want to go from one end to the other cause traffic density and jam while they pass through the city’s transportation filter. At the same time, these users are experiencing urban areas and places with known spatial habits. The method that is considered and applied as a solution to the traffic that is locked with this successive bunching and accumulation is the underground tunnels. The tunnel bypasses the regions where there are inadequate road networks with heavy traffic loads on the routes, connecting the one region to the other zones. The tunnel providing transit mobility mitigates the traffic load and also changes the known neighborhood of the urban areas. It changes the urban people’s usage maps in their heads and makes many different socio-economic regions closer and makes them neighbors. These tunnels open the way for radical changes in the harmonious structure of social, qualitative and economical gradual transition characteristics formed as a result of the natural and planned development of the city and open the door for radical changes. The use of land in very different structures interweaves the city-dwellers in socio-demographic structure. With the realization of these tunnels, the urban districts and centers become neighbors with these peripheries and carry the values of the qualified regions to these regions. In progress of time, the economic values of the periphery regions have increased, and the new business and residential areas have started to rise rapidly in these regions. It is observed that this activation is a positive effect of dynamism that will contribute to the development and progress of the periphery areas. It is thought that this positive effect bring with itself some problems such as some social problems as of excessive nesting of the peripheries with the qualified areas and the urban people with low income can be displaced with the increase in the economic value and their living areas can be changed and excluded. A three-step methodology was applied in the research. Entrances and exits of the tunnels were identified as working areas. The nearest circles to which effective access from these points are provided are the boundaries of the study area. The observations and determinations were made on the new settlement areas and points in the study areas. As a second step, their market values were searched and the real estate values before and after these tunnels were determined. The studies were performed on the maps; axial line maps were taken before and after the tunnel with the depthmapX program developed by the University College London, The Bartlett School of Architecture, and the depth values of the regions were examined. In the comparison performed, it was clearly observed that the high depth values that the old urban texture possesses in the analysis of the depthmapX axial line maps actualized with the tunnel are shifted to the fringe regions bounded by the tunnels. The market values of the regions in the economic context before and after the tunnels were determined and their maps were done. The new reconstruction maps were determined before and after the tunnel in the same way. The new structuring points and their market values were compared with the depth values of the regions and the presence of significant relationships between depth value / new structuring points and depth value / market value was determined. The tunnels, which were constructed with the aim of mitigating and balancing the traffic load, also changed the usual use of the city and determined that they took the urban development in different directions.