# The Impact of Distance and Altitude on Railway Environmental Noise Based on Cerebral Oxygenated Hemoglobin Saturation

## TL;DR

This study explores how railway noise affects brain activity, showing that proximity and altitude influence stress levels, offering insights for better railway planning.

## Contribution

The study is the first in Korea to use fNIRS to quantify cerebral activation due to railway noise at varying distances and altitudes.

## Key findings

- Brain activation due to noise was highest in the left DLPFC for altitude and in the left FPC for distance.
- Significant differences in activation were observed in specific Brodmann areas based on distance and altitude.
- Discomfort from railway noise was felt at closer distances, with no difference between building floors.

## Abstract

Railways are considered an environmentally sustainable mode of transportation but can pose significant environmental challenges due to their operation and associated activities. Among these, noise generation is a persistent source of public complaints. In Korea, a maximum distance of 100 m from buildings has been proposed for new railway developments in residential areas, although this guideline lacks a solid foundation based on experimental evidence. Noise barriers are often installed as a mitigation measure; however, there is no standardized guideline for their height in relation to their effectiveness at varying distances. The distances and altitudes set in this study took into account accessibility and the height of noise barriers on actual railway sites. In particular, we examined the effects of altitude above and distance from a railway site under the assumption that the prefrontal cortex would be physiologically affected by noise exposure. In this study, we conducted the first analysis in Korea of cerebral blood flow changes in response to noise, to assess quantitatively the stress effects caused by railway environmental noise at varying distances from, and altitudes above, a railway. Using functional near-infrared spectroscopy (fNIRS), we measured prefrontal cortex activation in 10 adult males (average age: 33.2 years). Brain activation was evaluated under different distances from (40 and 100 m) and altitudes above (1st and 4th floors of a building) a railway through a paired-sample t-test analysis. Discomfort was felt at relatively close distances to the railway, and there were no differences in perceived discomfort between the examined floors. Brain activation due to environmental noise was highest in channel 43 (left DLPFC) for altitude (floor) and in channel 37 (left FPC) for distance. Significant differences in activation were observed in the corresponding Brodmann areas, varying based on altitude and distance (p < 0.05). These results provide valuable scientific data for the preliminary design phase of new railway developments, particularly with regard to determining appropriate residential distance and noise barrier specifications, to enhance comfort of nearby residents. Furthermore, they may contribute to the improvement of quality of life by reducing stress caused by railway environmental noise.