Snohomish County
Transit Gap Analysis

Vulnerability — equal-weight composite of elderly population share, unemployment rate, zero-vehicle households, and low-income rate; normalized to [0,1] across block groups.

Accessibility — gravity model: A_i = Σ F_j · e^−βd_ij, β=4.0 (50% decay at 0.25 mi). Stop frequencies from Community Transit GTFS, March–June 2026.

Gap Score — vulnerability × (1 − normalized accessibility). Highest where need is greatest and service is weakest.

Priority — mean of normalized gap score and equity distance below the y=x service-equity line. Ranks underserved block groups for intervention.