Browser-Based Comparative Analysis of Environmental Health Routing Performance Across Global Metropolitan Areas

Pedestrian navigation systems overwhelmingly optimize travel time, yet health relevant environmental exposure along alternative paths remains under evaluated under deployed constraints. We present an automated, browser native benchmark of condition aware routing across six metropolitan areas (Tokyo, Shanghai, New York, London, Barcelona, Jakarta), with 360 paired evaluations (60 per city; 10 per city condition pair across six health profiles) on identical origin-destination (OD) endpoints. The active browser scorer computes a five factors environmental utility (air quality, temperature, humidity, noise, slope) via evidence tier, literature informed condition weights sourced from a single constants file, and selects the highest scoring candidate under a 5.0 km detour cap with a 0.5 km soft tolerance. The results are reported at three levels. Overall, strict environmental gain occurs in 75.83\% of route pairs, yet only 6.94\% achieve positive efficiency, indicating persistent mismatch between environmental improvements and operational utility. Conditional on exploitable route diversity, gain rates improve when geometry collapse pairs are excluded (collapse rate 11.1\%), showing that map provider topology is an important contributor but not the sole bottleneck. Fixed OD retest reliability (r ≈ 0.85) supports temporal score consistency under the benchmark protocol. The core contribution is a reproducible browser stack benchmark and a three level account of where environmental pedestrian routing produces benefit, where it adds only detour, and where deployment is not yet warranted.