Greenness visibility has been used as a useful index in landscape assessment. In this study, we also considered other major visible elements in urban streetscapes, sky and road, in landscape assessment to understand their relative contribution to preferences. We took 18 pictures in residential areas and calculated visibility ratios of greenness, sky and road. Afterwards, we conducted a landscape assessment experiment through web-based survey and conducted statistical analyses. As a result, we identified the threshold value of sky visibility, 15.6%, as a positive impression for sky openness. Similarly, we identified the threshold value of road visibility, 31.4%, as a positive impression for road openness. The thresholds of sky visibility were especially affected by the greenness visibility of the same picture. We also found that respondents’ impressions about the physical size of streets were strongly related to streetscape preferences, and road visibility had a strongly related to them. Therefore, we considered that ensuring the physical size of streets would be a key strategy to improve the visual quality of the streetscape in residential areas. Our results also suggested that personal orientation and residential attributes would be related to streetscape valuation and streetscape assessment based on regional characteristics would be necessary.