Consider the table given below providing details of traffic volume per hour for locations . When the total traffic volume is the same, the factor(s) which affect(s) the noise pollution level is/are

Location | Total traffic volume | % of Heavy Vehicles | Average noise level in dB (A) | Noise pollution level, in dB (A)
I | 377 | 24.4 | 73.5 | 84
II | 380 | 12.5 | 72.6 | 83
III | 377 | 30.0 | 73.5 | 86.5
IV | 225 | 12.5 | 72.98 | 80.9

When total traffic volume is constant, the vehicle composition—particularly the percentage of heavy vehicles—controls the noise level because heavy vehicles (trucks, buses) generate substantially higher noise from engines, exhausts, and tire/road interactions than light vehicles [1]. Empirical studies show that increasing the share of heavy vehicles (e.g., a 20% rise) significantly raises the measured road noise levels, confirming composition as a causal factor [2]. The term “average noise level” (Leq) is an indicator or metric used to quantify noise exposure over time rather than an independent causal factor; it describes the outcome, not a separate cause [3]. Hence option 1 is correct.

Sources

1. [1] Environment and Ecology, Majid Hussain (Access publishing 3rd ed.) > Chapter 6: Environmental Degradation and Management > 4. noise Pollution > p. 41
2. [2] https://www.researchgate.net/publication/229411101_Effects_of_traffic_composition_on_road_noise_A_case_study
3. [3] https://onlinepubs.trb.org/Onlinepubs/trcircular/175/175.pdf