Nowadays, most people believe that the greenway-system planning is one of the strategies to develop a sustainable city. However, most metropolitan areas are over-developed; there are no massive undeveloped areas left to create greenways. Under these circumstances, we propose redeveloping the current inter-city transportation system to create greenways, which meet the needs of ecological protection, recreation, and transportation. This research emphasizes on the Taichung Metropolitan Area (TMA), Taiwan. We first develop an assessment tool which includes GIS mapping techniques and an indicator valuation system to select appropriate roads from the current transportation system to create greenways. The indicator valuation system contains a series of indicators to evaluate the efficiency of each road in terms of 3 purposes: ecological protection, recreation, and transportation. The analyses reveal that 10 roads meet 3 purposes and 14 roads meet 2 purposes. We further apply the GIS grid technique to connect these roads to create the greenway network for the TMA. In summary, this paper develops a procedure to create the metropolitan greenway network to satisfy the multi-purposes of the public.