acoustics Article Comparison of Cabin Noise of Airport Express Rail Systems Heow Pueh Lee, Sanjay Kumar * , Saurabh Garg and Kian Meng Lim   Citation: Lee, H.P.;Kumar, S.; Garg, S.; Lim, K.M. Comparison of Cabin Noise of Airport Express Rail Systems. Acoustics 2022, 4, 1–13. https://doi.org/10.3390/ acoustics4010001 Academic Editor: Stéphane Moreau Received: 8 December 2021 Accepted: 27 December 2021 Published: 29 December 2021 Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affil- iations. Copyright: © 2021 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). Department of Mechanical Engineering, National University of Singapore, 9 Engineering Drive 1, Singapore 117575, Singapore; mpeleehp@nus.edu.sg (H.P.L.); saurabhgarg@mysoc.net (S.G.); limkm@nus.edu.sg (K.M.L.) * Correspondence: mpesanj@nus.edu.sg Abstract: In this paper, the cabin noise of four airport express rail systems, namely the Taiwan Taoyuan International Airport MRT, the Hong Kong Airport Express, RER B service from Paris Gare du Nord to Paris Charles de Gaulle Airport, and the Shanghai Maglev, have been measured. These four airport express rail systems have different specifications and maximum speeds, ranging from 100 to 300 km/h. The results show a significant low-frequency noise content below 100 Hz, which would not be captured if the measurements were conducted in dB(A). The difference between L eq in terms of dB(C) and dB(A) ranges from 11.3 to 17.0 dB. The maximum speed of the Taoyuan Airport MRT was found to be the lowest at 100 km/h and with the lowest L eq in terms of 66.4 dB(A) and 81.4 dB(C). The Shanghai Maglev has a maximum speed of 300 km/h but a relatively low L eq of 69.7 dB(A), although its top speed is almost three times the maximum of the other airport rail systems. It also has the lowest L max of 73.1 dB(A) among the four rail systems. Moreover, the Paris RER B railway system, with its top speed of 120 km/h, was measured to have the highest L eq and L max values of 72.8 dB(A) and 83.8 dB(A), respectively. Keywords: airport express; rapid transit; cabin noise; low-frequency noise; maglev 1. Introduction The overall success of air transport and airport-based economies typically depends on several factors, such as airport facilities, ease of movement within the airport, and connectivity between cities and airports. Unreliable or unpredictable connecting transport services between cities and the airport may cause travelers to miss a flight or miss a meeting. For example, Taxi passengers can be caught in a traffic jam during peak time or occasional traffic accidents, resulting in an unavoidable delay. Major airports usually contribute significantly to traffic on the roads around them. Therefore, planning for airports is generally accompanied by investments in highways and mass transit systems if impacts on road congestion and related air pollution need to be maintained within acceptable bounds. Over the past few decades, rapid transit systems or dedicated subways have provided a potential alternative solution for transferring people from the central city to the airport and vice versa. These services can quickly transport the bulk of passengers from one place to another among all types of road transports without potential traffic disruptions during peak hours. The high-speed express trains provide hassle-free, reliable, and comfortable transportation with ideally no time delay. In addition, the high-speed express train systems have often been associated with a reduced environmental footprint of the aviation industry, eventually helping towards attaining a sustainable urban environment [1]. The high-speed airport express rail systems have been successfully used in many countries to provide fast passenger rail transport from an airport to a nearby city by mainline or commuter trains, rapid transit, or light rail. Airport express rail systems have been popular solutions in European and Asian countries, such as Germany, France, Japan, China, Taiwan, and Singapore. The airport train service is among the first impressions of the city on the visitors. Any discomfort on commuters after a long flight might not be conducive to a good travel Acoustics 2022, 4, 1–13. https://doi.org/10.3390/acoustics4010001 https://www.mdpi.com/journal/acoustics