Evaluation and Analysis of Environmental Noise Levels in NCT of Delhi, India

Abstract

The present study reports the analysis of hourly equivalent noise levels of 100 sites in the NCT (National Capital Territory) of Delhi and correlates with the community perception that has not been reported so far. The study presents the environmental noise scenario of 100 sites in the NCT of Delhi, India, including 19 commercial, 9 industrial, 16 residential, 43 silence zones, 3 highway sites, and 10 intersection sites. The hourly equivalent noise levels of 100 sites were monitored at various timings between 9 AM and 8 PM to analyze the environmental noise pollution scenario in the city. Along with the hourly equivalent continuous sound levels (L_{Aeq, 1 h}); 10-percentile exceeded sound levels (L₁₀), Traffic Noise Index (TNI), Noise Climate (NC), and Noise Pollution Level (NPL) of these sites were also computed. The L_{Aeq, 1 h} levels varied from 66.5  to 84.7 dB(A), and majority of the sites (90.0% sites) exhibited L_{Aeq, 1 h} between 70  and 80 dB(A). A noise map was developed in addition to a socio-acoustic survey conducted to analyze the public perception toward noise pollution and associated health hazards. The study revealed that road traffic noise along with honking noise is the major dominant source of noise pollution. It shall be very helpful in recommending appropriate noise control strategies for abatement and control of environmental noise pollution in the city.

Introduction

Noise pollution is emerging as a silent disaster with the urbanization of the world. Although it has not been concerned as other kinds of pollution, even it has adverse physiological and psychological effects on living things [1]. It has been reported by the WHO (2005) that noise pollution is the third most hazardous to human health after air and water pollution [2]. Numerous factors influence the extent of noise in the urban areas including transportation (road/rail/air), industries, construction activities, music concerts, public address systems, loudspeakers at weddings and religious places, etc., but road transportation noise was observed to be the important factor in raising ambient noise level in the city [3–5]. Noise pollution has been recognized to have various disturbing health-related effects on human beings as confirmed by many studies across the world. It comes out in additional costs for the community [5, 6]. Depending upon the exposure time and loudness of noise, noise pollution can have numerous harmful effects including various physical effects like hearing loss and ear burning, physiological effects like blood pressure-related problems, psychological effects like stress and difficulties in sleeping, and work performance effects like reduced efficiency at the workplace [5, 7–9]. In India, generally, noise impact assessment studies have been done so far using traffic noise parameters equivalent continuous sound level (L_Aeq), 10-percentile exceeded sound levels (L₁₀), 50-percentile exceeded sound levels (L₅₀), 90-percentile exceeded sound levels (L₉₀), Traffic Noise Index (TNI), Noise Climate (NC), and Noise Pollution Level (NPL) [10–12]. The Guidelines Development Group of the World Health Organization (WHO) recommends that noise levels due to road traffic noise should be reduced below 53 decibels (dB) L_den. Also, for night noise exposure, it recommends reducing noise levels produced by road traffic below 45 dB L_night, at night-time [13]. The ambient air quality standards in respect of noise in India for all four zones are shown in Table 1 [14]. Numerous studies have reported on ambient noise monitoring in the Indian context. The Central Pollution Control Board (CPCB), India, has carried out several studies for monitoring ambient noise levels in Delhi city. The National Ambient Noise Monitoring Network (NANMN) project was established with the objective of collecting real-time noise monitoring data in seven cities in the country [14, 15]. Garg (2016) reported that only 9 out of 35 locations meet the ambient noise standard in seven cities of India considered in the NANMN project [16]. Mishra et al. 2010 carried out a traffic noise study in Delhi city along a rapid bus transit corridor. The relation between different noise parameters and noise annoyance was obtained using linear or multiple regression methods. In their study, a survey was also conducted which reported that 68% of subjects were exposed to stress due to noise pollution, 64% of subjects were exposed to hearing loss, 56% were exposed to blood pressure, 48% were exposed to depression, 36% exposed to agitation, and 12% exposed to fatigue [17]. Singh and Davar (2004) reported the effects of noise pollution on human health in Delhi. The study carried out that sleeping disorders and reduction in efficiency were the major effects on the people of Delhi due to noise pollution. In total, 83% of subjects of the community were annoyed due to the noise emission from loudspeakers. In total, 58% of respondents were affected due to the noise during religious functions. In total, 54% of subjects were annoyed due to neighborhood noise and 35% of subjects faced mentally tired and hearing problems due to the noise pollution [18]. Mohan et. al 2000 reported the traffic noise and survey response of the community residing in New Delhi. The study revealed that people living up to 30 m distance from arterial roads were exposed to much annoyance due to traffic noise. It also concluded that 70% of respondents desired to shift their residence from the nearside of roads due to the annoyance of noise pollution [19]. Jyoti et. al 2014 carried out an empirical study on noise pollution and a community survey among the people of Delhi. The study revealed that the majority of the subjects around 35% were highly exposed to hearing problems due to noise pollution. These respondents were of the age group of 40–60 years. On the other hand, people in the age group 20–40 years were highly exposed to communication interference, sleep disturbance, cause annoyance, and deafness [20]. Ahmed and Sarkar (2014) reported that residential areas are mostly affected due to vehicular traffic noise. The study carried out that during the night-time along an arterial road in Delhi, the equivalent traffic noise level varies from 63 dB to 66.7 dB(A) which is more than the limits recommended Ministry of Environment and Forest (MoEF), Govt. of India. The road traffic noise scenario in Delhi city is very dreadful on arterial as well as collector roads [21]. Garg et. al 2022 reported in a study on impact of COVID-19 lockdown on ambient noise levels in seven metropolitan cities in India that no silence or residential zone site complied with the ambient noise standards [22].

Table 1.

Ambient air quality standards in respect of noise in India [14]

			Limits in dB(A) Leq*
Area code	Category of zone	Day-time	Night-time
A	Industrial	75	70
B	Commercial	65	55
C	Residential	55	45
D	Silence	50	40

*Leq denotes the time weighted average of the sound level in decibels in A weighting

*Day-time is from 6.00am to 10.00 pm

*Night-time is from 10.00 pm to 6.00am

*Zone may be defined by the competent authority

“Authority” means and includes any authority or officer authorized by the Central Government, or as the case may be, the State Government in accordance with the laws in force and includes a District Magistrate, Police Commissioner, or any other officer not below the rank of the Deputy Superintendent of Police designated for the maintenance of the ambient air quality standards in respect of noise under any law for the time being in force [14]

Road traffic noise contributes around 55% of the total environmental noise in urban areas [23–25]. Honking is a major noise source in India irrespective of different road conditions, vehicular categories, and mixed traffic zones [26–28]. Vijay et. al 2015 study analyzes that honking contributes 2 to 5 dB(A) additional noise in total road traffic noise. Additionally, an increment in vehicular speeds from 35  to 55 km/hr provides a significant increment in road traffic noise levels by 4–5 dB(A) [3]. Kalaiselvi and Ramachandraiah (2016) reported that honking plays an important increment in noise scenario by the increment of 0.5–13 dB(A) in heterogeneous traffic conditions in India. It was also observed that noise prediction models developed for homogenous traffic conditions are not appropriately applicable for heterogeneous traffic conditions [29]. Thakre et. al 2020 reported that road traffic noise levels increased by 5–6 dB(A) between the period of seven years from 2012 to 2019 in Nagpur City. It was concluded that honking noise was increased by 4–6 times and traffic noise was increased by 1.7 times in this comparative study. The predicted noise levels (L_eq) were lying in the range of −1.7  to + 1.4 dB(A) [30]. Vijay et. al 2018 carried out a noise assessment study on urban agglomeration on the highway of Nagpur city. It was reported that honking noise contributes additionally to road traffic noise by 1–4 dB(A). A positive correlation was observed between honking events and noise levels, while negative correlations were observed for noise levels with vehicular speeds and traffic volume [31]. Singh et. al 2021 also considered honking events as an important parameter in developing the noise prediction model in the case study of Patiala city. A significant correlation was reported between equivalent continuous sound levels and honking events as well as the percentage of heavy vehicles [32].

Most of the Indian cities have been facing a severe problem due to noise pollution for the past few decades due to the constant growth of vehicles, urbanization, mixed traffic zones, and incompetent road networks [33]. The average road traffic noise is more than 70 dB(A) in most of the Indian cities [33]. It is quite cumbersome to perform noise monitoring in big metropolitan cities due to mixed traffic zones, heterogeneous traffic, miscellaneous vehicles, and inefficient traffic management at some sites [26, 28, 34]. Garg et. al 2017 also revealed that the implementation of the odd–even vehicular rule could not efficiently contribute to the reduction of the environmental noise scenario [35]. Therefore, an extensive noise monitoring study is required having the assessment on a large number of sites in Delhi city that has not been reported so far. It shall be very helpful to ascertain the environmental noise scenario and planning of appropriate mitigation measures that can be implemented to control noise pollution.

The present study is focused on the evaluation and assessment of hourly equivalent continuous noise levels at 100 locations in the National Capital Territory (NCT) of Delhi region. The work analyzes the environmental noise levels in major areas in the NCT of Delhi region. Along with this, a socio-acoustic survey on noise annoyance has been conducted at the same sites for ascertaining the public perception toward noise pollution and associated health hazards. The main objectives of the paper are:

• Evaluation and analysis of the hourly equivalent noise levels to assess the environmental noise scenario of NCT, Delhi.

• Assessment of correlation between the vehicular density of distinct categories and hourly equivalent noise levels.

• Assessment of correlation between the vehicular average speeds of distinct categories and hourly equivalent noise levels.

• Assessment of correlation between the number of honking events and hourly equivalent noise levels.

• Develop a noise map to assess the visual representation of noise scenario in the big metropolitan city.

• Conduct a community perception survey and inculcate awareness about the harmful effects of noise pollution in the community by direct interaction and displaying posters at various monitoring sites.

• Develop a noise exposure-effect relationship.

• Suggesting appropriate measures for noise abatement and control in NCT of Delhi.

This is the first extensive study of its kind which covers 100 noise monitoring sites for the NCT, Delhi, with the objective of understanding and assessing the environmental noise scenario of the city. The study shall also be helpful in analyzing the realistic environmental noise scenario of distinct zones of the city and adopting appropriate measures for noise mitigation and control.

Material and Methods

Measurements Sites Description

The study has been conducted in the National Capital Territory (NCT) of Delhi, India. The area of study (NCT of Delhi) is a part of the National Capital Region (NCR) of India [36]. The NCT of Delhi has an area of 1,483 km² and a population of around 16.8 million people in 2011, which is roughly 1.4 percent of the total population of India of about 1.2 billion people. Comparing rural–urban populations in the NCT, 97.5 percent of people reside in urban areas, whereas 2.50 percent live in rural areas [37, 38]. The road density of Delhi city is 2103 km/100km² which is the highest among all cities in India [39]. It is connected to different states of the country by 5 national highways NH 1, NH2, NH8, NH10, and NH24. Delhi city is the origin of the Golden Quadrilateral for Delhi-Mumbai and Delhi-Kolkata prongs. The city hosts three principal bodies of the Government of India; Rashtrapati Bhawan, Parliament House, and the Supreme Court of India. New Delhi is Municipality that comes under NCT [40]. New Delhi is located at 28°38′08″ N and 77°13′28″ E in the northern part of India [41].

The present study was conducted for 100 sites in NCT, Delhi, including 19 commercial zone sites, 9 industrial zone sites, 16 residential zone sites, 43 silence zone sites, 3 highway sites, and 10 intersection sites. The details of these 100 sites are represented in Fig. 1, created by using the Google Earth Pro 7.3.4.8248 (64-bit) desktop app [42]. Figure 2 represents a pictorial view of some of the important noise monitoring sites during the time of noise monitoring. The site selection strategy was based on choosing the traffic density of the measurement site lying in distinct zones in different ranges so that the 100 selected sites cover all kinds of traffic scenarios and all zones, i.e., commercial, residential, industrial, silence, and additionally highway, intersections, etc., in NCT of Delhi. It may be noted here that the classification of the site to lie in commercial, residential, industrial, or silence zone is decided by the competent authority [14]. The present study classifies these sites into various zones based on the preliminary inspection of the site characteristics.

Fig. 1.

Site map of 100 noise monitoring locations in NCT of Delhi [42]

Fig. 2.

Pictorial view of some noise monitoring locations in NCT of Delhi. a Safdarjung hospital, b AIIMS Delhi, c Lajpat nagar, d Akshardham temple, e Tis Hazari court, f Shahdara, g Rashtrapati Bhawan, h Kalinga Chowk-Patel nagar, i National stadium, j Indian institute of technology, Delhi, k Delhi secretariat

Environmental Noise Levels Data Acquisition and Analysis

The environmental noise data were monitored at hundred sites in NCT of Delhi using calibrated Norsonic Precision Sound Analyzer Nor145 for the duration of six months from December 2021 to May 2022. The microphone used was free-field, half-inch microphone of sensitivity of 50 mV/Pa. Along with this, a radar gun (Make: Bushnell) and video camera were used for measuring the average speed of vehicles and recording the hourly traffic density, respectively. These are traceable to national standards of sound pressure [43]. The Sound Level Analyzer was mounted on a tripod stand and fixed at a height of 1.5 m above the ground level and placed at about 7.5 m away from the center of the road, and 3 to 3.5 m away from walls to avoid reflections, if presented at any site, as per the standard guidelines mentioned in ISO 9613 [44]. Vehicular densities of distinct categories were measured by recording the traffic flow in video camera and counting them manually. The average speeds of vehicles were measured by using laser-based Radar Gun make Bushnell. The radar gun targeted on individual vehicular categories for measuring the average speeds. The honking events were measured by manually counting at the same time of noise measurement. The number of honking events per hour was taken to be considered in the methodology of the study. At each of the 100 sampling sites, A-weighted hourly equivalent continuous sound pressure levels (L_{Aeq, 1 h}) were monitored between 9 AM and 8 PM at the frequencies under the 1/3^rd octave range. Along with the L_{Aeq, 1 h}, 10-percentile exceeded sound levels, L₁₀, 50-percentile exceeded sound levels, L₅₀ and 90-percentile exceeded sound levels, L₉₀ was also monitored in order to assess the actual noise scenario due to road traffic and the background noise contributing to the noise data measured. Locations near activities like construction work or noisy social gathering events were avoided, and the monitoring of data was performed under appropriate meteorological conditions. Three crucial parameters, Noise Climate (NC) [45], Noise Pollution Level (NPL) [46], and Traffic Noise Index (TNI) [47] were also computed using the following three equations for describing the noise scenario of the city.

$$\text{NC}=L_{10}-L_{90}$$ 1

$$\text{TNI}=4\times \left(L_{10}-L_{90}\right)+\left(L_{90}-30\right)$$ 2

$$\text{NPL}=L_{50}+\text{NC}+{\text{NC}}^2/60$$ 3

Results and Discussion

Table 2 represents the hourly equivalent noise levels, L_{Aeq, 1h} of 100 noise-monitored sites of Delhi city, India, including 19 commercial, 9 industrial, 16 residential, 43 silence zones sites, 3 highway sites, and 10 intersection sites for the period from December 2021 to April 2022. Along with the L_{Aeq, 1h}, Table 2 also represents the 10-percentile exceeded sound levels, L₁₀, 90-percentile exceeded sound levels, L_90, 50-percentile exceeded sound levels, L_50, Traffic Noise Index, TNI, Noise Climate, NC, and Noise Pollution Level, NPL.

Table 2.

Hourly equivalent noise levels for 100 sites in NCT of Delhi

S. no	Name	Zone	Geographical Coordinates		LAeq	L10	L90	L50	TNI	NC	NPL
			Latitude	Longitude
1	Karol bagh	Commercial	28° 38′ 39.43" N	77° 11′ 19.82" E	77.7± 3.9	78.6	67.4	71.8	82.2	11.2	85.1
2	Mandir marg	Silence	28° 38′ 3.71" N	77° 12′ 2.17" E	73.8 ± 6.1	76.9	61.8	69.4	92.2	15.1	88.3
3	RML hospital	Silence	28° 37′ 29.21" N	77° 12′ 4.69" E	72.8 ± 3.6	74.7	66.6	70.1	69	8.1	79.3
4	Connaught place	Intersection	28° 38′ 6.12" N	77° 13′ 8.62" E	72.9 ± 4.4	75.4	64.7	68.6	77.5	10.7	81.2
5	National stadium	Commercial	28° 36′ 47.83" N	77° 14′ 12.95" E	73 ± 3.6	74.3	66.2	70.3	68.6	8.1	79.5
6	Lok Kalyan marg	Silence	28° 35′ 54.17" N	77° 12′ 9.74" E	71.5 ± 5.6	75	60.5	68.3	88.5	14.5	86.3
7	IMD	Silence	28° 35′ 24.33" N	77° 13′ 15.53" E	67.3 ± 6.2	71.2	54.8	61.8	90.4	16.4	82.7
8	JLN stadium	Commercial	28° 34′ 46.8" N	77° 14′ 1.51" E	73.2 ± 4.8	76.1	62.6	69.5	86.6	13.5	86
9	Nehru nagar	Residential	28° 33′ 57.6" N	77° 15′ 6.24" E	79.2 ± 3.1	81.3	74.1	77.4	72.9	7.2	85.5
10	Lajpat nagar	Commercial	28° 34′ 14.92" N	77° 14′ 11.05" E	76.3 ± 3.2	77.9	70.8	73.9	69.2	7.1	81.8
11	AIIMS	Silence	28° 34′ 1.33" N	77° 12′ 35.69" E	76.1 ± 3.2	77.5	70.3	73.4	69.1	7.2	81.5
12	Safdarjung hospital	Silence	28° 34′ 5.12" N	77° 12′ 28.85" E	78.1 ± 3.6	79.7	71.8	74.9	73.4	7.9	83.8
13	Rajendra place roundabout	Intersection	28° 38′ 32.07" N	77° 10′ 30.39" E	77.5 ± 4.3	79	69.1	73.3	78.7	9.9	84.8
14	NPL, PUSA road	Silence	28° 38′ 15.53" N	77° 10′ 28.33" E	74.6 ± 4.8	77.7	65.7	72.4	83.7	12	86.8
15	Punjabi bagh	Residential	28° 40′ 8.59" N	77° 8′ 14.1" E	79 ± 2.4	81	75.4	77.9	67.8	5.6	84
16	Paschim vihar	Residential	28° 40′ 13.56" N	77° 5′ 35.65" E	77 ± 2.9	79.1	72.4	75.3	69.2	6.7	82.7
17	Pitampura	Residential	28° 42′ 14.14" N	77° 7′ 51.03" E	76.7 ± 5.4	78.5	64.9	72.2	89.3	13.6	88.9
18	DTU	Silence	28° 45′ 11.02" N	77° 7′ 8.53" E	77.8 ± 4.8	80.2	68.4	73.2	85.6	11.8	87.3
19	Mundka	Industrial	28° 40′ 57.25" N	77° 2′ 11.33" E	75.1 ± 3.7	77.7	68.4	73.3	75.6	9.3	84
20	ITO	Intersection	28° 38′ 28.92" N	77° 13′ 38.24" E	79.9 ± 4.1	82.3	72.4	76.9	82	9.9	88.4
21	Patparganj	Industrial	28° 38′ 11.75" N	77° 18′ 38.58" E	77.7 ± 4.2	80.5	70.3	74.4	81.1	10.2	86.3
22	Anand vihar	Commercial	28° 39′ 3.35" N	77° 18′ 13.99" E	77.4 ± 3.4	79	71.5	74.8	71.5	7.5	83.2
23	CPCB	Commercial	28° 39′ 22.32" N	77° 17′ 40.62" E	83 ± 5.2	85	72.6	76.8	92.3	12.4	91.8
24	Vivek vihar	Residential	28° 40′ 14.74" N	77° 18′ 53.91" E	76.1 ± 4.6	78.1	67	72.1	81.4	11.1	85.3
25	Dilshad garden	Silence	28° 40′ 58.28" N	77° 18′ 43.94" E	74.4 ± 3.4	76.6	68.2	72.7	71.8	8.4	82.3
26	Kashmere gate	Intersection	28° 40′ 2.89" N	77° 13′ 41.59" E	80 ± 3.5	81.5	73.8	73.8	74.6	7.7	82.5
27	Civil lines	Silence	28° 40′ 53.85" N	77° 13′ 22.25" E	74 ± 4	76.2	66.6	71.8	75	9.6	82.9
28	Signature bridge	Highway	28° 42′ 19.49" N	77° 14′ 0.86" E	79.8 ± 3.2	82.1	74.3	78.2	75.5	7.8	87
29	Sonia vihar	Residential	28° 44′ 0.83" N	77° 14′ 55.71" E	75.9 ± 3.9	77	68.5	72.1	72.5	8.5	81.8
30	Shahdara	Commercial	28° 40′ 15.2" N	77° 16′ 13.56" E	79.1 ± 3.9	80.9	71.8	75.1	78.2	9.1	85.6
31	Wazirpur	Industrial	28° 41′ 49.8" N	77° 9′ 28" E	80.5 ± 3.7	82.8	74	77.4	79.2	8.8	87.5
32	Ashok vihar	Residential	28° 41′ 27.66" N	77° 10′ 35.33" E	73 ± 4.9	74.9	62.8	68.9	81.2	12.1	83.4
33	Jahangirpuri	Intersection	28° 43′ 44.61" N	77° 10′ 1.98" E	71.3 ± 6	73.9	58.8	65.1	89.2	15.1	84
34	Alipur	Silence	28° 48′ 8.52" N	77° 8′ 18.36" E	77.4 ± 5.5	78.7	65.6	70.9	88	13.1	86.9
35	Shalimar bagh max hospital	Silence	28° 43′ 41.39" N	77° 9′ 12.26" E	71.2 ± 6.9	73	55.1	64.1	96.7	17.9	87.3
36	Bawana	Silence	28° 48′ 9.04" N	77° 2′ 14.97" E	78 ± 4.8	80	68.5	73.8	84.5	11.5	87.5
37	IIT Delhi main gate	Silence	28° 32′ 45.23" N	77° 11′ 47.28" E	80 ± 2.9	81.2	75.1	77.9	69.5	6.1	84.6
38	IIT Delhi gate No 2	Silence	28° 32′ 41.56" N	77° 11′ 38.66" E	76.6 ± 3.9	77.4	69.1	73.3	72.3	8.3	82.7
39	Hauz Khas	Intersection	28° 32′ 39.46" N	77° 12′ 6.45" E	77.4 ± 4.6	79.1	68.2	72.3	81.8	10.9	85.2
40	AIIMS 2	Silence	28° 34′ 7.72" N	77° 12′ 51.62" E	77.1 ± 3.3	79.1	71.4	74.8	72.2	7.7	83.5
41	Okhla ITI	Industrial	28° 31′ 40.61" N	77° 14′ 49.72" E	74.9 ± 3.3	77.4	69.4	73.7	71.4	8	82.8
42	RK puram	Residential	28° 34′ 1.82" N	77° 10′ 35.03" E	79.9 ± 3	81.8	75	77.7	72.2	6.8	85.3
43	Dhaula kuan	Highway	28° 35′ 37.04" N	77° 9′ 50.7" E	79.9 ± 2.1	81.6	76.9	79	65.7	4.7	84.1
44	BLK MAX hospital	Silence	28° 38′ 35.82" N	77° 10′ 50.87" E	74.8 ± 4.3	72.9	63.8	67	70	9.1	77.4
45	Sir ganga ram hospital	Silence	28° 38′ 19.28" N	77° 11′ 22.83" E	74.7 ± 4.8	74.5	63.7	67.8	76.9	10.8	80.5
46	Sardar patel hospital	Silence	28° 38′ 50.63" N	77° 10′ 9.17" E	76.8 ± 5.3	76.2	64.2	69.8	82.1	12	84.2
47	Central secretariat	Silence	28° 36′ 54.42" N	77° 12′ 43.67" E	74.5 ± 4.1	76.8	67	71.6	76.3	9.8	83
48	India gate	Silence	28° 36′ 46.92" N	77° 13′ 39.82" E	75.2 ± 3.4	76.5	69.2	72.4	68.2	7.3	80.5
49	Supreme court	Silence	28° 37′ 19.84" N	77° 14′ 25.18" E	67.3 ± 5	70.5	57.6	63.8	79	12.8	79.3
50	Lady hardinge medical college	Silence	28° 38′ 9.9" N	77° 12′ 37.31" E	72.4 ± 5.2	73.5	60.8	67.5	81.6	12.7	82.9
51	LNJP hospital	Silence	28° 38′ 18.47" N	77° 14′ 18.94" E	77.1 ± 5.7	79.7	65.7	74.2	91.6	14	91.4
52	DU North campus	Silence	28° 41′ 24.35" N	77° 12′ 54.83" E	71.7 ± 5.1	74.4	61.5	68.5	83.1	12.9	84.2
53	Guru teg bahadur hospital	Silence	28° 41′ 5.67" N	77° 18′ 38.29" E	78.3 ± 5.4	79	66.2	72.2	87.2	12.8	87.7
54	Max hospital, Saket	Silence	28° 31′ 41.75" N	77° 12′ 41.17" E	75 ± 4.5	76.9	66	71.1	79.6	10.9	83.9
55	JNU university	Silence	28° 32′ 19.79" N	77° 10′ 27.87" E	74 ± 5.2	76.5	63.7	70.2	84.8	12.8	85.7
56	Kirti nagar	Industrial	28° 38′ 57.34" N	77° 8′ 35.89" E	77 ± 3.5	77.9	70.3	73.5	70.7	7.6	82.1
57	Rajouri garden	Residential	28° 38′ 28.9" N	77° 7′ 19.61" E	76 ± 3.4	76.5	68.6	72.5	70.3	7.9	81.5
58	Janakpuri	Commercial	28° 37′ 19.2" N	77° 5′ 16.62" E	80 ± 3.9	82.7	73.2	77.1	81.4	9.6	88.2
59	Fortis okhla Hospital	Silence	28° 33′ 35.42" N	77° 16′ 30.26" E	74.6 ± 4.9	76.4	64.6	69	81.6	11.8	83.1
60	Indraprastha apollo hospital	Intersection	28° 32′ 25.12" N	77° 16′ 55.76" E	80.1 ± 4.8	82.5	71	76.7	87.1	11.5	90.5
61	Jamia university	Silence	28° 33′ 40.73" N	77° 17′ 2.18" E	76.7 ± 4.3	78.8	69	73.9	78.1	9.8	85.2
62	Okhla industrial area	Silence	28° 31′ 55.17" N	77° 16′ 34.64" E	80.5 ± 3.1	82.1	75.4	77.9	72	6.7	85.3
63	Lotus temple	Silence	28° 33′ 8.97" N	77° 15′ 36.8" E	67.7 ± 4.9	71	58.4	64.8	78.8	12.6	80
64	Sarai Kale khan bus stand	Commercial	28° 35′ 14.12" N	77° 15′ 32.94" E	76.3 ± 2.9	78.1	71.5	74.8	67.8	6.6	82
65	Tees hazari court	Intersection	28° 40′ 1.1" N	77° 13′ 1.88" E	82.4 ± 4.8	83.8	72.9	76.7	86.5	10.9	89.6
66	Chandni chowk	Commercial	28° 39′ 2.5" N	77° 13′ 49.57" E	74.1 ± 4.2	76.2	66.3	70.9	75.9	9.9	82.5
67	New Delhi Railway station	Commercial	28° 38′ 36.21" N	77° 13′ 8.38" E	68.2 ± 4.7	69.8	58.6	63.3	73.2	11.2	76.5
68	Rashtrapati bhawan	Silence	28° 36′ 51.95" N	77° 12′ 44.11" E	73.2 ± 3	75.2	68.3	71.6	66	6.9	79.3
69	High court Delhi	Silence	28° 36′ 35.16" N	77° 14′ 11.76" E	74.5 ± 3.9	76.3	67.3	71.8	73.4	9	82.2
70	DU south campus	Silence	28° 35′ 22.45" N	77° 10′ 10.16" E	70.1 ± 5.2	72.5	59.4	65.1	81.8	13.1	81
71	Delhi secretariat	Silence	28° 37′ 47.44" N	77° 15′ 7.16" E	66.5 ± 5	69.4	57.1	61.3	76.2	12.3	76.1
72	UPSC bhawan	Silence	28° 36′ 27.64" N	77° 13′ 37.85" E	75.2 ± 4.1	77.8	68	72.2	77.4	9.9	83.7
73	Vasant kunj	Residential	28° 31′ 44.88" N	77° 8′ 57.29" E	76.4 ± 4.3	78.1	67.6	73.1	79.7	10.5	85.4
74	Qutub minar	Silence	28° 30′ 47.14" N	77° 11′ 11.08" E	75.9 ± 5.9	77.3	62.6	69.9	91.3	14.7	88.1
75	DST mehrauli road	Silence	28° 32′ 22.69" N	77° 11′ 16.83" E	74 ± 5.2	76.5	63.8	70	84.7	12.7	85.4
76	Munirka	Commercial	28° 33′ 28.21" N	77° 10′ 25.65" E	76.5 ± 4.7	77.7	66.7	71.8	80.7	11	84.8
77	Sarojini market	Commercial	28° 34′ 33.2" N	77° 11′ 54.08" E	75.1 ± 4.8	76.7	65.3	70.4	80.9	11.4	84
78	Patel nagar-kalingachowk	Intersection	28° 38′ 53.67" N	77° 9′ 50.33" E	84.7 ± 4.8	87.1	75.5	80	91.8	11.6	93.8
79	Shadipur	Residential	28° 39′ 5.73" N	77° 9′ 30.8" E	80.4 ± 3.5	82.4	74.5	77.6	76.2	7.9	86.6
80	Moti nagar	Residential	28° 39′ 44.14" N	77° 8′ 29.3" E	79.6 ± 3.6	81.8	73.3	76.8	77.2	8.5	86.4
81	Tilak nagar	Commercial	28° 38′ 13.09" N	77° 5′ 46.51" E	73.6 ± 3.3	75.7	68	71.7	68.8	7.7	80.4
82	Krishi bhawan	Silence	28° 36′ 57.87" N	77° 12′ 51.27" E	75.6 ± 3.7	78	69.1	73.3	74.5	8.8	83.5
83	Vigyan bhawan	Silence	28° 36′ 37.85" N	77° 13′ 7.98" E	72.1 ± 5.1	74.7	61.8	68.4	83.5	12.9	84.1
84	Jor Bagh	Residential	28° 35′ 10.6" N	77° 12′ 45" E	69.7 ± 5.8	72.8	58.2	65.6	86.4	14.5	83.7
85	Chanakyapuri embassy area	Silence	28° 35′ 47.57" N	77° 11′ 32.35" E	75 ± 4.5	77.1	66.2	72.7	79.6	10.9	85.5
86	Moti bagh	Residential	28° 34′ 59.22" N	77° 10′ 5.79" E	78.2 ± 2.5	80	74.7	76.9	65.9	5.3	82.7
87	Delhi cantt	Highway	28° 36′ 43.72" N	77° 6′ 56.38" E	79.4 ± 3	80.1	74.4	76.7	67.1	5.7	82.9
88	Old Delhi Railway Station	Commercial	28° 39′ 40.82" N	77° 13′ 40.3" E	78.9 ± 5.1	80.6	68.2	73.1	87.8	12.4	88.1
89	Sarai rohilla railway station	Commercial	28° 39′ 44.54" N	77° 11′ 27.04" E	72.1 ± 4.7	73.1	62.7	67.5	74.5	10.5	79.8
90	Samaypur badli	Commercial	28° 44′ 41.77" N	77° 8′ 16.43" E	78.4 ± 4.2	78.2	68.8	72.9	76.7	9.5	83.9
91	Rohini	Residential	28° 44′ 11.02" N	77° 4′ 53.15" E	71.1 ± 3.9	73.9	64.2	68.9	73	9.7	80.2
92	Azadpur mandi	Commercial	28° 42′ 52.95" N	77° 10′ 37.31" E	72.9 ± 4.6	75.6	64.2	69.9	79.8	11.4	83.4
93	Daryaganj	Commercial	28° 38′ 42.82" N	77° 14′ 25.02" E	75.5 ± 4.4	77.9	67.5	72.2	79.2	10.4	84.4
94	Laxmi nagar	Residential	28° 38′ 13.6" N	77° 16′ 35.56" E	78.2 ± 3.5	80.4	72.2	75.9	74.9	8.2	85.1
95	Akshardham temple	Silence	28° 37′ 8.51" N	77° 16′ 46.21" E	75.8 ± 2.9	77.5	71.2	73.8	66.3	6.3	80.7
96	Naraina	Industrial	28° 37′ 48.38" N	77° 8′ 18.23" E	76.4 ± 5.3	77.1	64.4	70.4	85.2	12.7	85.8
97	Subhash nagar	Intersection	28° 38′ 35.45" N	77° 6′ 25.09" E	76.5 ± 4.1	77.8	68.8	72.3	74.9	9	82.7
98	Lawrence road	Industrial	28° 41′ 8.79" N	77° 9′ 42.49" E	77.6 ± 4.9	78.3	66.8	72.5	82.8	11.5	86.2
99	Anand parbat	Industrial	28° 39′ 27.46" N	77° 11′ 1.71" E	78.9 ± 4.3	80.5	70.9	75.2	79.3	9.6	86.3
100	Mangolpuri	Industrial	28° 41′ 33.78" N	77° 5′ 30.82" E	77 ± 3.6	78.9	70.6	74.5	73.6	8.2	83.9

It can be observed from Table 2 that L_{Aeq, 1h} varied in the range 66.5 to 84.7 dB(A). The minimum level of 66.5 dB(A) was observed at the Delhi Secretariat (S), and the maximum level of 84.7 dB(A) was observed at Kalinga Chowk, Patel Nagar (C). This can be attributed to the fact that the commercial zone areas are also exposed to noise due to commercial activities (e.g., market activities, excessive honking due to heavy rush in market places, continuous shouting, and public address systems in some of the areas) along with the road transportation noise. Along with this, L₁₀ is the statistical index that is commonly used for assessing traffic noise in an area and it can be observed from Table 2 that the highest value of L₁₀ was observed to be 87.1 dB(A) at Kalinga Chowk, Patel Nagar (C), and the minimum value of L₁₀ was observed to be 69.4 dB(A) at Delhi Secretariat (S). However, L₉₀ is usually used to quantify the background noise levels and it can be seen from Table 2 that the minimum value of L₉₀ was observed to be 54.8 dB(A) at IMD (S), while the highest value of L₉₀ was observed to be 76.9 dB(A) at Dhaula Kuan (H) site. It is due to the fact that the IMD (S) site is less exposed to background noise because no background noise sources are present there except for the minimal road traffic flow, while Dhaula Kuan is a highway zone site that is continuously exposed to the honking and vehicle engines noise because of the high traffic density at highway zones. The Traffic Noise Index (TNI) represents the extent of variation in traffic flow, and the value of TNI over 74 dB (A) is defined as the threshold of over criterion [47]. It can be seen from Table 2 that TNI is varying in the range of 65.7 dB(A) to 96.7 dB(A) and only 32 sites out of 100 sites exhibited TNI under the threshold limit of 74 dB(A). Also, noise climate (NC) is the range over which the sound levels are fluctuating in an interval of time and it was revealed from Table 2 that the value of NC varied in the range from 4.7 to 17.9 dB(A). Also, the value of Noise Pollution Level (NPL) varied in the range of 76.1–93.8 dB(A). Figure 3a shows the L_{Aeq, 1h} of 100 noise monitoring sites, and it can be seen from the figure that no site complied within the 60 dB(A) L_{Aeq, 1h} limit [48]. Also, Fig. 3b represents the L₁₀ values of 100 noise monitoring sites. It can be seen from Fig. 3b that except for one site (Delhi Secretariat), no other site complied with the 70 dB(A) L₁₀ limit recommended by the National Building Code (2016) [49]. Furthermore, a frequency spectrum of L_Aeq,1h at some of the selected sites is shown in Fig. 4. It can be seen from Fig. 4 that the peak is observed at 40 Hz to 80 Hz in lower frequencies, while for the higher frequencies, the peak is observed at 2.5 to 4 kHz.

Fig. 3.

a A-weighted hourly equivalent continuous sound levels (LAeq,1 h). b Hourly 10-percentile exceeded sound levels (L10) of 100 sites in NCT of Delhi

Fig. 4.

Frequency spectrum of hourly equivalent noise levels at some of the selected sites

In order to study the correlation between the hourly equivalent noise levels (in dB(A)) and the traffic density (no. of the vehicle per hour) of the vehicles, the coefficients of determination (R²) were computed between the hourly equivalent noise levels and density of all types of vehicles present on the roads in the NCT of Delhi and also with the number of honking events per hour. The number of vehicles on the road varied in a large range of 1647 to 8825 vehicles per hour, and the total average speed of vehicles varied in a range of 23.6 to 46.5 km/hr. The coefficients of determination (R²) between the traffic densities (Q) and hourly equivalent noise levels are represented in Table 3. It can be observed from Table 3 that the maximum correlation was reported between the total traffic density and hourly equivalent noise levels, while that of minimum correlation was reported between the heavy vehicle density and hourly equivalent noise levels. The coefficient of determination between the total traffic density and the hourly equivalent noise levels was found to be higher than that between all individual categories of vehicles and environmental noise levels. Further, to find out the correlation between the hourly equivalent noise levels (in dB(A)) and vehicular average speeds, the coefficients of determination (R²) were also computed between the hourly equivalent noise levels and average speed of all types of vehicles present on the roads in the NCT of Delhi. The coefficients of determination (R²) between the vehicular average speeds (V) and hourly equivalent noise levels are represented in Table 3. It can be observed from Table 3 that the maximum correlation was reported between the total average speed and hourly equivalent noise levels, while that of minimum correlation was reported between the average speed of heavy vehicles and hourly equivalent noise levels. The coefficient of determination between the total average speed and the hourly equivalent noise levels was found to be higher than that between all vehicular average speeds of individual categories of vehicles and environmental noise levels.

Table 3.

Coefficients of determination (R²) of vehicular densities (Q) of different categories and vehicular average speeds (V) of different categories with hourly equivalent noise levels of 100 sites in the NCT of Delhi

Vehicle category (Q)	R2	Vehicle Category (V)	R2
Light vehicles density	0.65	Average speed of light vehicles	0.45
Medium vehicles density	0.63	Average speed of medium vehicles	0.44
Heavy vehicles density	0.59	Average speed of heavy vehicles	0.41
Total traffic per hour	0.74	Total average speed per hour	0.69

Also, a good correlation of R² = 0.68 was observed between the number of honking events per hour and the hourly equivalent noise levels. It was revealed from this analysis that vehicles running on the road contribute to elevating environmental noise levels to a significant extent. Figure 5a to d represents the correlation between the traffic density of vehicles of different categories and the hourly equivalent noise levels. Additionally, Fig. 5e represents the correlation between the number of honking events per hour and the hourly equivalent noise levels.

Fig. 5.

Correlation of vehicular density (a light vehicles, b medium vehicles, c heavy vehicles, d total traffic), and e honking with hourly equivalent noise levels at 100 sites in NCT of Delhi

Zone-Wise Analysis

In order to assess the environmental noise scenario in all distinct zones of the NCT of Delhi, a zone-wise analysis was also conducted. The frequency distribution of hourly equivalent noise levels in distinct zones for 100 sites in the NCT of Delhi is shown in Table 4.

Table 4.

Frequency (in percentage) of day equivalent noise levels in distinct zones for 100 sites in NCT of Delhi

Level range dB(A)	Industrial (N = 9)		Commercial (N = 19)		Residential (N = 16)		Silence (N = 43)		Highway (N = 3)		Intersections (N = 10)		Overall (N = 100)
	No of sites	Frequency percentage (%)	No of sites	Frequency percentage (%)	No of sites	Frequency percentage (%)	No of sites	Frequency percentage (%)	No of sites	Frequency percentage (%)	No of sites	Frequency percentage (%)	No of sites	Frequency percentage (%)
55–60	0	0.0	0	0.0	0	0.0	0	0.0	0	0	0	0	0	0
60–65	0	0.0	0	0.0	0	0.0	0	0.0	0	0	0	0	0	0
65–70	0	0.0	1	5.3	1	6.3	5	11.6	0	0	0	0	7	7
70–75	2	22.2	7	36.8	2	12.5	22	51.2	0	0	2	20	35	35
75–80	7	77.8	10	52.6	13	81.3	16	37.2	3	100	6	60	55	55
80–85	0	0.0	1	5.3	0	0.0	0	0.0	0	0	2	20	3	3

Industrial Zone

Noise monitoring was conducted for 9 industrial sites out of 100 monitoring sites. It can be observed from Table 4 that out of nine sites, 7 sites exhibited L_{Aeq, 1h} in the 75 dB(A) to 80 dB(A) range, while only 2 sites exhibited L_{Aeq, 1h} in 70 dB(A) to 75 dB(A) range. Also, it can be seen in Fig. 3a and b that no industrial zone site had day equivalent noise levels less than 60dB(A) L_{Aeq, 1h} limit and 70 dB(A) L₁₀ limit [48, 49].

Commercial Zone

Noise monitoring was conducted for 19 commercial sites out of 100 monitoring sites. It can be observed from Table 4 that more than half of the commercial zone sites (52.6 %) exhibited L_{Aeq, 1h} levels within the range 75 dB(A) to 80 dB(A), while 36.8% of the commercial zone sites exhibited L_{Aeq, 1h} levels within 70 dB(A) to 75 dB(A) range. It can also be observed from Fig. 3a and b that no commercial zone site had day equivalent noise levels less than 60dB(A) L_{Aeq, 1h} limit and 70 dB(A) L₁₀ limit [48, 49].

Residential Zone

Noise monitoring was conducted for 16 residential sites out of 100 monitoring sites. It can be observed from Table 4 that the majority of the sites (93.8 % of the sites) exhibited L_{Aeq, 1h} levels within the range 70 dB(A) to 80 dB(A), while one residential zone site exhibited L_{Aeq, 1h} level within 65 dB(A) to 70 dB(A) range. It can be also seen from Fig. 3a and b that no residential zone site had day equivalent noise levels less than 60dB(A) L_{Aeq, 1h} limit and 70 dB(A) L₁₀ limit [48, 49].

Silence Zone

Noise monitoring was conducted for 43 silence sites out of 100 monitoring sites. It can be observed from Table 4 that 38 sites out of a total of 46 silence zone sites reported L_{Aeq, 1h} levels within the range 70 to 80 dB(A), while only 5 sites (10.9%) exhibited L_{Aeq, 1h} in 65 dB(A) to 70 dB(A) range. Also, it can be seen from Fig. 3a and b that no silence zone site had day equivalent noise levels less than 60dB(A) L_{Aeq, 1h} limit, while only one silence zone site, Delhi Secretariat, had day equivalent noise levels less than 70 dB(A) L₁₀ limit [48, 49].

Highway Sites

Noise monitoring was conducted for 3 highway sites out of 100 monitoring sites. It can be observed from Table 4 that all 3 highway sites exhibited L_{Aeq, 1h} within the range 80 to 85 dB(A) range. It can also be observed from Figs. 3a and b that no highway site had day equivalent noise levels less than 60dB(A) L_{Aeq, 1h} limit and 70 dB(A) L₁₀ limit [48, 49].

Intersection Sites

Noise monitoring was conducted for 10 intersection sites out of 100 monitoring sites. It can be observed from Table 4 that out of ten sites, 8 sites exhibited L_{Aeq, 1h} in the 70 dB(A) to 80 dB(A) range, while only 2 sites exhibited L_{Aeq, 1h} in 80 dB(A) to 85 dB(A) range. It can also be observed from Figs. 3a and b that no intersection site had day equivalent noise levels less than 60dB(A) L_{Aeq, 1h} limit and 70 dB(A) L₁₀ limit [48, 49].

However, the noise-monitored data were of hourly equivalent noise levels, while the ambient noise limits are for 16 hours for day-time and 8 hours for night-time. However, the hourly equivalent noise levels provide an indication of the noise scenario of various sites and the identification of noisy hot spots.

Noise Map of NCT of Delhi

Noise mapping is a very competent method to describe the graphical or visual representation of sound level distribution in the study area [50]. It is a practical assessment method to ascertain the environmental noise scenario in urban and metropolitan cities that is very useful in the planning of noise mitigation measures for big cities. A noise map generally represents the environmental scenario in form of contours. These contours show the various color code zones that signify the intensity and frequency of noise levels in the study area. Noise mapping provides the planning of new roads on nearby structures in urban areas. Using Inverse Distance Weighting (IDW) method, the noise map is created for 100 sites in the NCT of Delhi by using ArcGIS v10.8 software as shown in Fig. 6.

Fig. 6.

Noise map of 100 noise monitoring sites in NCT of Delhi using by ArcGIS v10.8

Environmental Noise Perception Survey

In order to disseminate awareness toward the harmful effects of noise pollution in the community, hoardings were displayed at various noise monitoring sites. Along with this, oral discussions and written survey regarding noise annoyance due to various noise sources were also conducted. The hoardings displayed at the noise monitoring sites are shown in Fig. 7. In order to understand the community's perception toward the annoyance due to environmental noise pollution, a socio-acoustic survey on noise annoyance was created in which a questionnaire of six questions is using Google form. The survey was distributed among the community of different age groups via hybrid mode, i.e., physically and online mode (WhatsApp, Gmail, and other social media platforms). A total of N=554 participants were requested for taking part in the survey. The respondents were mainly the community exposed to the noise levels at various sites mentioned in Table 2. The participants included 23% of females and 77% of males. In this socio-acoustic survey, people of various age groups were requested to participate. Furthermore, 24% of participants were below 15 years, 18% of participants were between 15 and 25 years, 36% of participants were between 26 and 40 years, 17 % of participants were between 41 and 60 years, and 5% of participants were above 60 years. A summary of some demographic details of the survey participants is shown in Table 5. Also, a source apportionment analysis has been performed to find out the dominant noise source experienced at various noise-monitored sites. Figure 8 represents that road traffic noise along with honking noise is the most dominant noise source among the various noise sources.

Fig. 7.

Hoardings and banners used at various sites in NCT of Delhi for observing noise awareness week during December 18th to 25th, 2021, and on routine days during noise monitoring for inculcate awareness about noise pollution among the community

Table 5.

Basic socio-demographic features of survey participants (N = 554)

Parameter		Frequency (%)
Gender	Male	77.0
	Female	23.0
Age (years)	< 15	24.0
	15–25	18.0
	26–40	36.0
	41–60	17.0
	> 60	5.0
Educational qualification	High School	23.4
	Graduate	31.5
	Post-Graduate	27.1
	Doctorate	18.0
Residential area	North Delhi	20.0
	South Delhi	26.3
	East Delhi	32.6
	West Delhi	21.1
Noise sensitivity	Highly sensitive	31.0
	Medium sensitive	39..0
	Low sensitive	25.0
	Not sensitive at all	5.0
	Highly sensitive	40.4
	Medium sensitive	31.7
Noise annoyance	Low sensitive	19.4
	Not sensitive at all	8.5
Health effects due to noise*	Stressed	15.0
	Sleeping disorders	25.0
	Hypertension	11.0
	Hearing impairment	7.0
	Mentally tired and headache	34.0
	Other Health effects	8.0

*Multiple options were asked and reported by respondents

Fig. 8.

Source Apportionment Analysis obtained from socio-acoustic survey among community (N = 554) in the NCT of Delhi

The outcomes of the survey are pictorially represented as Pie charts shown in Fig. 9. It can be observed that 14% of the community was not even aware of the health effects due to noise pollution, while 33% of the community knew well about noise pollution and its effects. Also, it was asked the community how much they feel as a noise-sensitive person and 39% of the community responded that they did not see themselves as a noise-sensitive person, while 31% of the community were highly sensitive toward the noise. Besides that, it was observed that 46% of the community was moderately annoyed by the traffic noise, while 23% of the participants were extremely annoyed by the traffic noise. In total, 32% of the community felt extremely annoyed by the honking noise, while 36% of the community felt slightly annoyed by the honking noise. Additionally, it is highlighted that 10% of the community felt extremely annoyed by the construction noise, while 44% of the community felt moderately annoyed by the construction noise. Furthermore, the health effects of noise pollution faced by the community were also questioned through the survey and it was revealed from the survey that the majority of the community felt mentally tired and headache due to the noise pollution, while 25% of the community were having sleeping disorders due to the noise. Besides the questionnaire, an exposure–effect relationship was also derived between the hourly equivalent noise levels, L_{day, 1h,} and percentage of highly annoyed people, %HA, as well as the percentage of annoyed people, %A, for honking dominant and less-honking areas. Linear regression method is used to derive this exposure–effect relationship. The minimum limit for hourly equivalent noise levels (L_{Aeq, 1h}) was considered to be as 60 dB(A) in the Indian perspective unlike that of 42 dB(A) in European scenario [13]. The derived relationships are represented in Table 6.

Fig. 9.

Results of socio-acoustic survey conducted among various individual sites in NCT of Delhi

Table 6.

Exposure–effect relationship developed from noise monitoring and socio-acoustic survey at various sites in NCT of Delhi

Scenario	Equation	R2
Traffic noise	%A = 1.5985 (LAeq,1 h-60) + 14.469	0.32
	%HA = 2.0851 (LAeq,1 h-60) + 8.066	0.35
Traffic noise and honking noise dominant areas	%A = 2.0434 (LAeq,1 h-60) + 0.7534	0.34
	%HA = 1.9621 (LAeq,1 h-60) + 18.833	0.40

* %A= Percentage annoyed, %HA= Percentage highly annoyed

Environmental Noise Control in the NCT of Delhi

An effective noise control strategy shall be very helpful in the implementation of appropriate mitigation measures. The following major causes of noise pollution were observed during the noise monitoring at various sites in the NCT of Delhi:

• Road traffic with distinct category vehicles,

• Unnecessary honking,

• Heavy vehicles in restricted zones,

• Heterogeneous traffic conditions,

• Railway/metro noise,

• Industrial and construction activities,

• Loudspeakers at religious places,

• Public addresses systems,

• Loud music in social functions,

• Ambulance and police van sirens,

• Aircraft noise,

• Transformers and diesel generators,

• Lack of maintenance of noise barriers,

• Poor road surface conditions.

It was observed during the study that there was the mixed type of zones for the majority of sites which causes an increment in the noise scenario. Mixed zones generally consist of residential and commercial activities like the houses and markets are situated very near in some areas. It is irrelevant to classify them as silence, residential, or commercial zone. The highest equivalent noise level was reported at Patel Nagar-Kalinga Chowk being 84.7 dB(A), which is a mixed zone (i.e., residential and commercial zone) comprised of various other noise sources along with transportation noise like commercial activities and households/domestic noise, etc. At one of the commercial sites (Munirka), noise barriers erected on the flyover were in damaged condition, which was acting as the secondary noise source. Due to this, the community was highly annoyed by wind striking on the damaged barriers.

Therefore, an effective noise control policy for a sustainable environment and integrated noise mitigation measures for urban planning is essentially required for big metropolitan cities. The control plans should be cost-effective and feasible so that can be attributed to reducing noise pollution [50]. The National Policy Planning Framework (NPPF) regarding environmental Noise Management and Control had been discussed by Garg (2022) [51]. Figure 10 discusses various feasible noise control measures to reduce environmental noise levels in the NCT of Delhi. In order to control ambient noise levels, the following mitigation measures should be implemented:

• Unnecessary honking of vehicles should be prohibited.

• Application of green spaces on dividers and along the roads.

• Proper lane driving of heavy vehicles.

• Heavy vehicle entry should be restricted in silence and residential zones.

• Proper sustaining of noise barriers along the roads.

• Constructional activities guidelines for noise control should be developed.

• Smart Traffic Management; a proper following of traffic signals and traffic rules.

• Identification, surveillance, and noise monitoring of noisy hotspots.

• Redressal of noise pollution complaints through various methods such as helpline no., online web portals, apps (like Green Delhi app, SAMEER app), etc.

• Inculcating noise awareness among the community through FM channels, print media, and social media platforms like Facebook, WhatsApp, Twitter, etc.

• Proper implementation of the Motor Vehicle Act (1988) for vehicles older than 15 years.

• The noise emission for diesel generators should be controlled by using canopy of higher insertion loss.

• Police vans, public address systems, etc., should also be managed for less noise impact on the community.

• Absorptive road surfaces can contribute to the reduction of noise levels [52–55].

Fig. 10.

Various noise control measures

Conclusions

The present study is the first comprehensive study in the past few decades with an objective of noise monitoring and assessment of environmental noise scenario at 100 sites in the NCT of Delhi, India. The hourly equivalent noise levels were monitored at 100 sites including 19 commercial, 9 industrial, 16 residential, 43 silence zones, 3 highway sites, and 10 intersection sites that were analyzed. A noise map is developed for these sites by using ArcGIS v10.8 software in the present study. Along with this, a socio-acoustic survey was also conducted at the same sites to assess the perceptual response of the community exposed to road traffic noise. The important conclusions from the study are derived as:

• It was revealed from the source apportionment analysis that road traffic noise along with honking was observed to be the major source of noise pollution in the NCT of Delhi. In total, 78% of subjects experienced road traffic noise with honking as the most dominant source of noise pollution.

• The hourly equivalent noise levels of the 100 monitored sites were observed to be varied in the range of 66.5–84.7 dB(A), while the majority of almost 90.0% of the sites exhibited hourly equivalent noise levels within 70 dB(A) to 80 dB(A) range.

• It was observed from the study that the maximum hourly equivalent level was reported at Kalinga Chowk, Patel Nagar, which is a commercial zone site, while the minimum hourly equivalent level was reported at the Delhi Secretariat, which is a silence zone site.

• It was revealed that TNI varied in the range of 65.7–96.7 dB(A) and only 32 sites out of 100 sites exhibited TNI under the threshold limit of 74 dB(A) [47].

• Good correlations of R² > 0.59 were observed between the hourly equivalent noise levels and distinct vehicular densities as well as total traffic density. Moderate correlations of (0.41 < R² < 0.45) were observed between hourly equivalent noise levels and vehicular average speeds of distinct categories, while a good correlation of R² = 0.69 was observed between hourly equivalent noise levels and the average speed of total traffic. Also, a good correlation of R² = 0.68 was observed between the number of honking events per hour and the hourly equivalent noise levels.

• It was carried out from the socio-acoustic survey that 32% of subjects were highly annoyed due to the honking noise, while 36% of subjects were slightly annoyed due to the honking noise. In total, 25% of subjects were exposed to sleeping disorders, 34% of subjects felt mentally tired and headache, and 11% of subjects were exposed to hypertension due to road traffic noise.

• A linear regression relationship was developed between noise exposure and annoyance by utilizing the result of the environmental noise perception survey that can facilitate the noise impact assessment for the development of new projects, elevated metro corridors, highways, etc., in the NCT of Delhi.

The current study reported the alarming situation of the environmental noise scenario in the NCT of Delhi, India. Therefore, extensive noise monitoring and analytical study are urgently required for making sustainable noise action policies for noise control in Delhi—NCR. Future studies will be targeted at noise monitoring of more number of sites of free-flowing traffic, highways, intersections, and industrial zone in the NCT of Delhi. The socio-acoustic survey shall also be carried out at more number of sites, and multiple logistic regression analysis shall be undertaken to develop an exposure–effect relationship. Also, an indigenous noise prediction model will be developed based on the present study.