Utilizing the green view index to improve the urban street greenery index system: A statistical study using road patterns and vegetation structures as entry points

Urban streetscapes play a critical role in ecological benefits and resident health. The green view index (GVI) can improve the limitations of the existing road greenery index, which is too planarized. This study used road patterns and vegetation structures to explore the intrinsic connection and application possibilities between the GVI and the urban road greenery indicators. The study acquired and then selected 27,038 valid street images to calculate the GVI through semantic segmentation, and used ArcGIS10.6 to calculate the greenery land ratio (GLR) and greenery coverage ratio (GCR) for 593 roads. After strictly controlling of the variables, typical roads were selected for simulation scenario comparison experiments. The results indicates that the GVI will be lower than the greenery volume of two-dimensional indicators, and a threshold within 30% can be set as a preliminary reference of the GVI standard for urban streetscapes. The GVI is irreplaceable and has a more flexible range, which provides a more comprehensive, accurate and rigorous evaluation of the greenery volume. The central greenery belt and the shrub layer are essential to enhance GVI. From all researched viewpoints, the Tree-Shrub and Tree-Shrub-Herb structures have similar GVI values. The roads with the 4-bar pattern have the greatest potential for GVI improvement. The impact of the divided greenery belts to affect the GVI may lower than the central greenery belt. In addition, the arbors are critical in enhancing the GVI, but for roads in the early stage of construction or when aiming to improve the GVI level, the application of shrubs should be considered first rather than the perfection of the vegetation structure. This study verifies the necessity of utilizing the GVI to improve the urban greenery index system and provides a quantitative reference for the practical application of the GVI, constructive comments on the greenery volume construction of urban streetscapes, and future research directions for the GVI.