**4. Results**

Early on in this research, when exploring potential case studies, it was evident that the common ground of early green street implementers in the US was stormwater management. All three cases (and many other cases explored in the case selection process mentioned in the methods section) were related with stormwater regulation. The story started in 1983, when the US Environmental Protection Agency (EPA) released a report proving that stormwater was not harmless [61]. The EPA was especially concerned with the discharges of combined waters (stormwater and wastewater). These combined sewer overflows (CSOs) occurred during heavy storm events in cities, generating vast discharges of combined waters into the bodies of water. If combined sewer discharges were central in the debate, separate sewer discharges also were found as not harmless. In 1987, when Congress amended the Clean Water Act, local governments became responsible for finding ways to control stormwater to protect surrounding waters.

Different cities adopted different strategies. Besides the traditional alternatives (e.g., separating the sewer systems), the purpose of green alternatives is to provide permeable areas in order to mimic previous urban conditions in which the soil perviousness facilitated water retention and delayed runoff [7,62]. Green streets and green roofs are examples of green stormwater infrastructures (GSI) to retain or detain runoff, and thus reduce pollution

discharges into US waters. By GSI, we mean rain gardens, bioswales, bio strips, infiltration planters, street trees, and all permeable areas that provide one or more environmental services.

Each case study has the same structure. First, there is a general introduction of the case with the story of how green streets came into existence locally. Next, the description focuses on the street planning and design process and how GSI was introduced within the ROW. Finally, for each case, the variables that each city took into account to develop their approach are presented, as well as the proposed process to achieve green streets. Here, for the sake of simplicity, the term "green street" refers to a street that contains green infrastructure even though it is sometimes used differently, for example in Seattle.
