Where Should Street Trees Be Planted? A Behaviour-Informed Design Framework for Adelaide Main Streets

Greening-priority methods can identify under-greened locations, but they do not necessarily tell designers what tree intervention should follow. This study develops a behaviour-informed decision-support framework and applies it as a pilot on four Adelaide main streets. The analysis uses 93,155 warm-season pedestrian observations across 100 approximately 20 m segments. A Pedestrian–Greenery Priority Index (PGPI) combines standardised pedestrian flow with deficits in Green View Index (GVI) and canopy cover. The 20 highest-ranked segments included 16 on Hindley Street and four on Gouger Street. A second-stage Lingering Index (LI), based on the pooled percentile rank of prolonged-stay share, was used to distinguish support- and enable-oriented roles within the PGPI shortlist before site-feasibility screening. Four corridor scenarios compared planting intensity, followed by species selection based on design role, climate suitability, and available space. On Hindley, Balanced used 52.2% as many added trees as Maximum while retaining 57.8% of the Maximum increase in the corridor canopy design estimate; on Gouger, the corresponding values were 56.3% and 49.2%. These ratios are reported as scenario comparisons, not as evidence of greater canopy efficiency. The approximately 20% GVI reference was informed by an earlier Adelaide pedestrian-duration analysis but is used only as a study-specific scenario reference, not an empirically established design target or universal threshold. The approximately 20 m analytical unit, 120 s operational classification, approximately 20% GVI reference, and species inputs are study-specific. The transferable contribution is the decision sequence, which can support municipal street-tree programmes and main-street revitalisation by linking priority, design role, feasibility, planting amount, and species choice.