Technical note AstudyofnoiseinCNGdrivenmodesof transport in Delhi S.Anyogita,AmitPrakash,V.K.Jain* School of Environmental Sciences, Jawaharlal Nehru University, New Delhi 110067, India Received 1 June 2002; received in revised form 9 June 2003; accepted 28 July 2003 Abstract Measurements of noise and its spectral characteristics were made inside various types of transport running on Compressed Natural Gas (CNG) fuel in Delhi. Noise indices L 10 , L 50 , L 90 and L eq were estimated from the measured noise levels for vehicles in neutral gear, slow speed (speed 420 km/h) and under free flow (speed 530 km/h) conditions. It is found that background levels, when averaged over all speeds, are maximum in Rural Transport Vehicles (RTV)followedbyBuses,Auto-rickshawsandTaxis.Withincreaseinthespeed,noiselevelsare appreciablyenhancedexceptinthecaseofauto-rickshawswheretheincreaseismoderate.The spectraldistributionsofnoiseinsidevehiclesobtainedat1-octavebandfrequencies,showarather similarnature.ThestudyrevealssignificantlylowernoiselevelsinsideCNGdrivenpublicmodes oftransportcomparedtothosefoundinanearliersurveyinsidedieselandpetroldrivenvehicles. # 2003ElsevierLtd.Allrightsreserved. Keywords: Noise;CNGfuel 1. Introduction Noise is a well known environmental problem associated with major cities world wide.Agreatdealofefforthasbeendevotedtoextensivenoisesurveysandmodel- ling studies in various cities of the world [1–9]. In most of the surveys, vehicular traffichasbeenidentifiedasamajorfactorcontributingtourbannoise.Theimpact oftrafficnoiseexposureonhumanbeingsintermsofannoyancehasbeenexamined byusingvariousstatisticalnoiseindicesinanumberofstudies [10–13].Mostofthe abovementionedstudiespertaintooutdoornoisemeasurements.Alimitednumber Applied Acoustics 65 (2004) 195–201 www.elsevier.com/locate/apacoust 0003-682X/$ - see front matter # 2003 Elsevier Ltd. All rights reserved. doi:10.1016/j.apacoust.2003.07.007 * Corresponding author. Fax: +91-11-26162276. E-mail address: vkj0400@mail.jnu.ac.in (V.K. Jain).