Operating　fixed　water-based　firefighting　systems　(FFFS)　might　affect　the　performance　of　other　parts　of　an　integrated　tunnel　safety　system,　particularly　the　longitudinal　ventilation　system.　The　interaction　of　the　water　spray　discharged　from　two　FFFS　(with　and　without　foam),　with　the　longitudinal　ventilation　system　in　a　new　city　tunnel　under　construction　was　studied　by　full-scale　burning　tests.　Results　of　the　study　under　large　fires　up　to　20　MW　in　diesel　pool　fires　or　wood　pallet　fires　are　reported　in　this　paper.　The　impact　of　longitudinal　ventilation,　the　activation　sequences　of　the　ventilation　system　and　the　fixed　fire-fighting　system,　and　the　performance　of　the　two　FFFS　in　suppressing　vehicular　fires　with　and　without　shields　to　fire　sources　were　evaluated.　Results　are　expected　to　be　useful　for　drafting　appropriate　fire　codes　on　fire　suppression　systems　for　controlling　urban　tunnel　fires.