Introduction Urban sprawl, increasing vehicle numbers, and the need for new transport technologies have driven the construction of metro and regional rail systems in South Asian countries like India. These large-scale urban rail—Regional Rapid Transit system (RRTS) and Metro—projects, while essential, have significant noise impacts, especially on sensitive areas near metro alignments, such as schools, hospitals, and residential buildings housing vulnerable populations like the elderly and disabled. Unlike conventional railways, urban rail systems require specific design standards and adhere to host country regulations regarding rolling stock and locomotives. There is limited knowledge about noise propagation and management in the context of these developmental projects. While scientific studies and simulations are used to assess noise impacts, urban rail systems—like other public goods—are both non-rival and non-excludable. Communities benefit from these greener and more convenient transport options but also face health and safety risks when metro lines are close to residential areas. This article offers best practices with a focus on community welfare. How are urban rail projects in India regulated and assessed for noise impacts? Urban rail projects in India are regulated by the Ministry of Urban and Housing Affairs (MOHUA) under the Metro Policy-2017. They must follow the Guidelines for Noise and Vibrations set by the Track Design Directorate of the Research Designs and Standards Organization (RDSO), Ministry of Railways, issued in September 2015. These guidelines are based on a comprehensive study by the Federal Transit Administration (FTA) of the United States Department of Transportation. Additionally, the World Bank’s IFC General EHS Guidelines for Noise Standards[1] are often referenced during noise assessments. Noise assessments for urban rail projects involve monitoring baseline conditions and modeling future scenarios using tools like Sound Plan, based on the ISO 9613 standard for outdoor sound propagation, and FTA/FRA-HSGT:2005 for railway noise. The design of metro systems, including locomotives and track structures, is crucial as these are the primary sources of noise during operation. If noise levels exceed acceptable limits, additional mitigation measures, such as high-efficiency noise barriers, are implemented. Noise levels in rapid rail transit can vary significantly. For instance, when trains travel on elevated viaducts at speeds around 50 mph (approximately 80 km/h), noise levels can reach 85 A-weighted decibel or dB(A) at 15 meters from the tracks. On the ground level, the noise may be around 80 dB(A), while at stations, it is typically about 65 dB(A). The main contributors to these noise levels are the train operations and the track structures. The impact of noise is influenced by various factors, including: Type of metro system (elevated or underground) Design speed Distance between stations Operational hours and frequency of trains Maximum acceleration and deceleration Sensitivity and proximity of receptors (e.g., residential areas) Height and elevation of the viaduct Type of residential receptors (e.g., multi-story apartments or houses) Type of urban environment (metro, urban agglomeration, suburban areas) Cumulative impacts from other noise sources What noise mitigation measures are used in metro rail projects? In the Delhi Meerut RRTS, which traverses through the urban areas of Delhi, Ghaziabad, and Meerut, specific design measures were implemented to reduce noise impacts on the surrounding communities. The design incorporated ballast-less tracks, signaling systems, dumpers, shock absorbers, and a viaduct structure specifically shaped to reduce noise. Additionally, 3-meter-high noise barriers were installed for a 125-meter section of the viaduct, along with ballast-less long welded rails to minimize noise near the alignment. The viaduct, constructed from concrete and steel, was designed to direct the primary noise upward, with the rail level 24 meters above the ground and 8.37 meters above roof level. The viaduct height in a 100-meter section was also increased beyond the standard height for the rest of the alignment. The Chennai Metro presented a moderately different scenario, as it included both elevated and underground sections passing through dense urban areas with high-rise residential buildings. The design incorporated ballast-less tracks supported by two layers of rubber pads and skirting on the coach shells to screen noise from the rail-wheel interaction. Polycarbonate noise barriers, ranging from 15mm to 25mm in thickness, were also used to reduce noise levels by 30 to 33 dB. The alignment, located along the median of an arterial road, required specific noise barrier designs: Barriers close to vehicles: Located 1 to 3 meters above the top of the rail, these barriers effectively reduced noise by 6 to 10 dB. Barriers at the ROW Line: For trains on the far track, the height of these barriers was increased to maintain effectiveness, ensuring noise reduction did not drop below 3 dB, even when the barrier obstructed the line-of-sight. Figure 1: 3D Isopleth Showing Noise Propagation from a Typical Metro Project Source: Nitesh Patil - ADB staff consultant. Nagpur Metro Phase II has the least operational noise impact, as it primarily connects suburban areas with mostly single-story residential buildings. Only a few sensitive receptors, such as hospitals and educational institutions, were identified for noise assessment. The alignment's average speed was set at 32-34 km/h (around 20-21 mph). The design included baffles and parapets up to rail level, resilient mounting, dampers, and welded rails. Noise modeling simulations indicated that noise levels were within permissible limits. However, noise barriers were still recommended as a good practice, along with ballast-less tracks supported by two layers of rubber pads and skirting on the coach shells. While numerous studies exist on rail noise-efficient technologies, CSIR-CRRI scientists have developed advanced noise barrier designs based on different frequency ranges[2]. These barriers are tailored to address specific disturbing frequencies generated by railways and metros, particularly the screeching sound caused by train-track friction on curved sections. Conclusion Noise impacts from urban rail projects are complex and cumulative, especially in densely populated urban areas where background noise is already significant. Effective management of these impacts requires early planning, particularly in large-scale metro projects with both elevated and underground sections. Simulating noise levels and embedding abatement measures throughout the project lifecycle can significantly mitigate noise impacts. Advanced noise abatement technologies used in metro projects can also be applied in similar urban environments across South Asia and Southeast Asia, including Bangladesh, Indonesia, Thailand, Malaysia, and the Philippines. Figure 2: Projected Noise Level Scenarios for the Three Metros Source: Nitesh Patil - ADB staff consultant. Recommendations Enhanced public engagement. Increase community consultations during the design phase to incorporate feedback from affected residents and institutions, ensuring that noise mitigation strategies meet local needs. Adoption of advanced technologies. Prioritize the use of advanced noise abatement technologies, such as frequency-specific noise barriers and resilient mounting systems, to reduce noise impacts, particularly in densely populated areas. Ongoing monitoring and adaptive management. Mandate continuous monitoring of noise levels during construction and operation, with provisions for adaptive management to address any exceedances in real-time. Holistic approach to noise management. Urban planners and policymakers should integrate metro projects with broader urban noise regulations, addressing other significant noise sources like vehicular traffic, industrial activities, and public infrastructure. While urban rail projects are often perceived as major contributors to urban noise pollution, the scientific basis for this perception is limited compared to other noise sources. Effective noise management requires not only project-level assessments but also a broader regulatory focus on all urban noise sources to comprehensively improve living quality in urban environments. [1] The Indian standard limits noise levels for the 12-hour Leq-dB(A) to a maximum of 65 dB(A) during the day and 55 dB(A) at night in commercial areas, and 75 dB(A) during the day and 70 dB(A) at night in industrial areas. These standards align with IFC guidelines. For residential properties, the standard limits noise levels to 55 dB(A) during the day and 45 dB(A) at night. [2] Low-Frequency Noise Barrier Configuration (Technology 1), Mid-Frequency Noise Barrier Configuration (Technology 2), and High-Frequency Noise Barrier Configuration (Technology 3) Ask the Experts Suvalaxmi Sen Safeguards Specialist, Office of Safeguards, Asian Development Bank Suvalaxmi Sen has nearly 20 years of experience in environmental and social impact assessments, developing management plans, performing due diligence, and documenting environmental and social risk summaries for private equity funds and international banks. She has in-depth knowledge of the transport sector and expertise in air and noise simulation models for predicting project exceedances. Suvalaxmi has extensive experience in the energy, financial institutions, manufacturing, oil and gas, and logistics sectors. She is a certified Lead Auditor for ISO 14001 and ISO 18001. 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