Application of sustainable transportation policies for resolving the transportation problem of Istanbul that has a population of 14.7 million in 2015 is of vital importance. This study focuses on economical and social goals of sustainable transportation by researching the relationship between urban accessibility, affordability and the transportation system. The purpose of this study is to investigate the combined role of affordability and accessibility and to introduce an accessibility measure to compare different transportation infrastructure schemes in Istanbul. For this purpose, the accessibility has been measured by means of a joint logit model. The main outcomes have been shown on an accessibility map and an elasticity analysis has been presented for different user groups. It has been concluded that accessibility is much higher in the central areas and decreases in the outskirts of the city. Results of the joint logit function have indicated that the effects of gender, income and car availabilities on mode choice are significant. The elasticity analysis has shown that mode choice decisions of car users are not sensitive to the transportation cost.