Study of noise hazard in bus interior in Dhaka City

Abstract

The problem of urban mass transit noise pollution is universal and in the past few decades it has grown to the point that it has become a major concern for both the public and the policy-makers. Dhaka is one of the most heavily populated metropolitan cities of the world with significant commuter flows. The scenario of bus interior noise level in Dhaka city has got worse due to very old bus engine, weak physical condition of buses and poor maintenance of bus fleet. The awareness regarding the noise hazards of mass transportation in Dhaka city almost absent due to limited research work on occupational noise hazard related to mass transit networks. Continuous noise level measurements were carried out approximately for a total of 39 hours in 29 buses on almost all bus routes in Dhaka city. Noise indices L10, L50, L90 and Leq were estimated from measured noise levels for 29 bus trips. Stair graphs of Leq were portrayed for 29 bus trips and also for selected 9 bus routes in Dhaka city. The noise indices L90 varied between 65.8 dBA (Azmiriglori bus) to 77.3 dBA (Midway bus) and L50 ranged between a minimum of 72.9 dBA (BRTC AC bus) to a maximum of 82.2 dBA (Dipon transport and Konok Poribahan). The maximum L10 (90 dBA) was experienced in Shatabdi poribahan whereas minimum (79 dBA) was experienced in BRTC AC bus. Three kinds of noise maps were constructed for Dhaka city bus routes to visualize overall bus interior noise hazard scenario and to identify hotspots of noise pollution in Dhaka city bus routes. The maximum average equivalent continuous noise level (88 dBA) was found in Mirpur-12 to Mirpur-10 route segment whereas the minimum average equivalent continuous noise level (77 dBA) was found in Kakrail to Shatrasta route segment. Noise exposure metrics were calculated to obtain an understanding regarding the nature of the noise exposed as well as to provide comparison with the permitted noise exposure levels as per National Institute for Occupational Safety and Health (NIOSH) guidelines. After correction for working shift, the range of noise exposure was found to be ranging from 79.8 dBA (Azmiriglori bus) to as high as 92.9 dBA (Dipon transport bus). The shift length of 24 buses exceeded the permitted shift length as per NIOSH guidelines whereas for 5 buses the shift length did not exceed NIOSH guidelines. Nine buses among 29 buses exceeded Noise Dose as per NIOSH guidelines. According to NIOSH guideline the most severely noise polluted bus services were BRTC bus, Dipon transport and Konok Poribahan. Experienced Noise Exposure Levels (LEX) in BRTC bus, Dipon Transport and Konok poribahan bus were 91.5dBA, 92.9dBA and 90.8dBA respectively. For these noise exposure levels the permitted shift length according to NIOSH guidelines are 1.78 hours, 1.3 hours and 2.1 hours respectively but actual average shift length for these buses were 14.4 hours. The lowest LEX (79.8 dBA) and the lowest Noise Dose (31%) were found in Azmiriglori bus which operates on Sadarghat to Abdullapur route. From this study significant influence of bus velocities, age of bus engine, number of intersection on specific bus routes, types of engine and impact of outside noise levels were found on bus interior noise level. Findings of this research work showed that level of noise hazard in bus transportation in Dhaka city urban area is high enough to adversely affect the health and productivity of bus driver and conductor as well as its residents. With the rapidly growing rate of infrastructural development, unplanned urban land-use change and weak transportation system it is almost certain that problem of bus interior noise pollution will soon assume a critical dimension and will be a cause of increasing concern for both public and responsible policy-makers.