Coverage, Directness, and Connectivity: An Ex Ante Diagnostic Framework for Planned Urban Rail Corridors

Urban rail investments can improve accessibility and support compact development, but their effectiveness depends on spatial and infrastructural conditions that are observable before operation. This study proposes an ex ante diagnostic framework for planned corridors based on three dimensions: coverage, directness, and connectivity. Coverage captures urban opportunity within graduated pedestrian catchments of 600–800 m, scaled to the urban context of each station group, through built-up intensity, activity concentration, and land-use diversity. Directness compares route and straight-line distances at corridor, segment, and individual link scales. Connectivity measures station integration with existing bus and rail services and road-based feeders within 300 m using a Network Connectivity Index (NCI). Applied to Antalya’s planned 4th Stage Rail System Line in Türkiye (20 stations; five segments), the framework reveals substantial spatial variation. Built-up ratios range from 0.10% to 29.47%, with no station leading all coverage indicators. The end-to-end directness ratio is 0.898, while the five contiguous segments range from 0.874 to 0.996; indirectness is not distributed evenly but concentrates at three turning points that, together, account for 47% of the corridor’s total angular deviation. NCI values range from 0.000 to 0.708 (mean 0.363), and rankings remain stable across nine weighting scenarios (Spearman’s ρ = 0.994–1.000). Rather than aggregating dimensions, the framework compares them to identify mismatches and guide targeted pedestrian, feeder-integration, and station-area interventions.