Environmental　safety　issues　and　ventilation　problems　caused　by　the　construction　of　urban　tunnel　have　increasingly　been　attracting　people＇s　attention.　Previous　studies　in　China　have　mainly　focused　on　vehicle　emissions　and　ventilation　control　technologies　in　road　tunnels,　resulting　in　a　research　gap　on　urban　tunnel　ventilation　engineering　design.　Therefore,　a　detailed　monitoring　investigation　was　conducted　from　May　22　to　June　2,　2013　in　Changsha　Yingpan　Road　Tunnel,　China.　The　study　aim　was　to　measure　the　traffic　characteristics,　air　velocity　and　the　carbon　monoxide　(CO),　nitrogen　oxides　(NO,)　and　fine　particulate　matter　(PM2.5)　concentrations　in　this　tunnel,　which　has　two　lanes　per　bore　and　multiple　ramps.　Measurement　results　show　that　during　the　workday　morning　peak,　the　maximum　traffic　flow　was　1560　passenger-car-unit/h　per　lane　with　vehicle　speed　around　33.6　km/h　in　the　eastbound　tunnel,　the　average　air　velocity　was　3.07　m/s,　and　the　proportion　of　the　light-duty　vehicles　(LDV)　was　97.3%.　Under　the　traffic　force　(not　open　fan),　the　CO　and　NO　average　concentrations　at　the　main　tunnel　outlet　were　20.3　ppm　and　1.65　ppm,　respectively.　The　gas　pollutant　concentrations　are　effectively　controlled　within　the　multiple-ramps　tunnel　and　the　design　air　volume　flow　is　noticeably　reduced.　The　traffic　air　flow　was　found　to　provide　32.5%　of　the　required　air　volume　to　dilute　NOx　in　blocked　traffic　condition　(vehicle　speed　of　10　km/h).　In　addition,　the　PM2.5　concentration　is　mainly　affected　by　the　value　of　background　outside　the　tunnel.　The　result　can　provide　a　quantitative　assessment　method　to　support　pollutant　concentration　control　and　contribution　of　requested　air　volume　by　traffic　flow　in　urban　complex　structure　tunnel.　(C)　2015　Elsevier　Ltd.　All　rights　reserved.