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Review of Related Literature Foreign Literature The most recognized problem is the need for congestion relief in city streets. Over the last few decades, many cities have constructed roadway tunnels to improve their traffic conditions and to adapt the road network to the predicted demand. Tunnels have been used since the 19 th century to provide a grade- separated space to make individual car transport and public transportation faster and independent from local traffic and natural barriers. The success of subways and road tunnels continues to be seen in the expansion of existing systems world-wide and creation of new metros as the urban population demand more rapid transportation. Hundreds of hours per worker per year can be saved in this way, as the cost of congestion in OECD countries is estimated to be equivalent to about 2 percent of the GDP (Godard, 2008). Continually improving tunneling and excavation support technology adds to the success of urban rail systems (Broere, 2012). Local Literature

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