What is the main environmental concern associated with high motor vehicle traffic?

The main environmental concern associated with high motor vehicle traffic is air pollution. Motor vehicles emit a variety of harmful pollutants, including nitrogen oxides, carbon monoxide, particulate matter, and volatile organic compounds. These emissions contribute to the formation of ground-level ozone, smog, and respiratory problems in humans.

High traffic levels can lead to increased concentrations of these harmful substances in urban areas, negatively impacting air quality and posing health risks to the population. The effects of air pollution due to motor vehicles can also extend beyond human health, contributing to environmental degradation, such as climate change through greenhouse gas emissions.

While water pollution, soil degradation, and noise pollution are indeed important environmental issues associated with transportation, the direct and more critical impact of high motor vehicle traffic is primarily seen through its contribution to air pollution, making it the most pressing concern in this context.