Subway Environment Research Articles

Correlation between levels of airborne endotoxin and heavy metals in subway environments in South Korea

This study aimed to evaluate the exposure levels and variation in airborne endotoxin and heavy metals such as aluminum, chromium (Cr), iron (Fe), manganese (Mn), nickel (Ni), zinc, and lead (Pb) in the three different South Korean subway environments (driver room, station office, and underground tunnel) and identify subway characteristics influencing endotoxin and heavy metals levels. Air samples were collected and analyzed using the kinetic Limulus Amebocyte Lysate assay and inductively coupled plasma mass spectrometers. The geometric mean was determined for endotoxin levels (0.693 EU/m3). It was also found that Fe (5.070 µg/m3) had the highest levels in subway environments while Pb (0.008 µg/m3) had the lowest levels. Endotoxin levels were higher in the underground tunnel and lower in the station office; the total heavy metal levels showed the same pattern with endotoxin levels. Endotoxins and total heavy metal levels were higher in the morning than at night. Positive correlations were found between endotoxin and Cr, Fe, Mn, and Ni levels. Given the correlation between airborne endotoxins and heavy metals, further studies with larger sample sizes are needed to identify the correlation between levels of airborne endotoxin and heavy metals.

Overall and thermal comfort under different temperature, noise, and vibration exposures

Public transports like the bus and subway inherently experience noise, vibration, and temperature variations that are different from building environment. Each of them can influence passengers' comfort, but little is known about their combined effects, especially how they affect thermal comfort. This paper presents experimental results from a series of human subject tests under different noises, vibrations, and temperatures. 32subjects' subjective perception and physiological response were collected under three temperatures (22.5, 25.5, 28.5℃), five noise levels (55, 60, 65, 70, 75dB(A)), and five vibrating accelerations (0, 0.2, 0.4, 0.6, 0.8m/s2 ). We also varied the noise and vibration spectrums to simulate the bus and subway environments. In total, 48 195-min and 192 115-min laboratory tests were conducted. By using significance tests (paired t tests and two-way ANOVA tests) and sensitivity analysis (Treed Gaussian Process), the results show that temperature, noise, and vibration exposures can significantly affect subjects' overall satisfaction. More interestingly, high noise and vibration levels can cause warmer thermal sensations. A change in the noise of 20dB(A) or vibration of 0.6m/s2 is equivalent to an ambient temperature change of 0.6 °C. We also observed higher heart rates and metabolic heat production at higher levels of noise and vibrating accelerators. Based on the test results, regression models were developed to describe the combined effects of temperature, noise, and vibration on subjects' overall comfort perception and thermal neutral temperature. They can serve as references for the design and operation of public transport environments.

Dinâmicas da inovação: automação integral da condução e agência humana na Linha 4 do metrô de São Paulo

Considero o metrô como um complexo sistema de comunicação, abrangendo dispositivos tecnológicos (que enviam mensagens operacionais para manter o fluxo dos trens) e pessoas (passageiros e operadores que interagem entre si e com mecanismos). Os circuitos comunicativos de um metrô são arranjos híbridos de interfaces que geram um ambiente midiático onde tecnologia e agência humana se imbricam. Tenho investigado, em pesquisa etnográfica, a reconfiguração dos circuitos comunicativos no contexto da Linha 4 do metrô de São Paulo, que opera com trens totalmente automáticos. Na situação de automação integral da condução, o componente tecnológico do ambiente do metrô é enfatizado — condutores são substituídos por computadores de bordo sob a supervisão de uma sala de controle, mecanismos são introduzidos no edifício do metrô e o pessoal de estação tende a ser reduzido. Uma outra materialidade se constrói no ambiente do metrô com a predominância da operação remota que as tecnologias digitais estipulam. No caso da Linha 4, contudo, o número mais expressivo de agentes nas estações e a presença de agentes nos trens automáticos, preparados para automação desassistida, mostram que o projeto não se realizou plenamente. Neste artigo, apresento alguns elementos do conjunto de explicações e comentários de profissionais ligados, de várias maneiras, à implementação da Linha 4 para a questão da assistência nos espaços da linha, particularmente no que concerne ao fenômeno da presença humana nos trens. Exploro também, com apoio em conversas com passageiros e na observação participante, como se desdobra no quotidiano das viagens. A tensão entre o previsto e o realizado tem se apresentado como um componente expressivo das complexas dinâmicas da recepção social da inovação na Linha 4 do metrô de São Paulo. Palavras-chave: Inovação. Circuitos Comunicativos. Metrô (São Paulo).

Locally Resonant Periodic Wave Barriers for Vibration Isolation in Subway Engineering

Subway transportation is being promoted worldwide to effectively solve urban congestion. However, the vibration induced by subway traffic has caused a major adverse impact on building safety, precision instrument operation and human health. Wave barriers have been proven effective in mitigating ground vibration, whereas they have some limitations in achieving ideal attenuation zone and high efficiency to cover the low-frequency vibration in underground railway system. Based on locally resonant phononic crystals theory, this paper designs three-component locally resonant periodic wave barriers (LRPWBs), and investigates the effects of geometrical and material parameters on the bandgap features in detail. The band structures are calculated using improved plane wave expansion (IPWE), the transmission spectra and vibration modes are obtained by finite element method (FEM). The results indicate LRPWBs are able to give lower and wider bandgap to cover the main frequency of subway environment, which is proved by time and frequency domain analysis. For the bandgap mechanism, the local resonance features of LRPWBs result in the energy conversion between kinetic energy and elastic strain energy, thus the elastic wave energy is localized in resonance unit and then the locally resonant bandgap is created. In addition, the bandgap can be adjusted by carefully selecting proper geometrical and material parameters to actualize low-frequency broadband attenuation. Further studies about multi-oscillator system indicate that the appropriate combination of multiple LRPWBs are conductive to diverse and broad bandgaps. The investigations can provide inspiration for periodic wave barriers design in multi-frequency vibration attenuation field.

Using miniaturised scanning mobility particle sizers to observe size distribution patterns of quasi-ultrafine aerosols inhaled during city commuting

Portable miniaturised scanning mobility particle sizer (SMPS) instruments measuring atmospheric particles within the 10–241 nm size range were used to track particle number size distributions and concentrations during near-simultaneous pedestrian, bicycle, bus, car, tram and subway commuting journeys in Barcelona, Spain on 4th-6th July 2018. The majority of particles in this size range were <100 nm, with k-means cluster analysis identifying peaks at 15–22 nm, 30–40 nm, and 45–75 nm. Around 10–25% of the particles measured however were >100 nm (especially in the subway environment) and so lie outside the commonly defined range of “ultrafine” particles (UFP, or <100 nm particles). The study demonstrated in detail how personal exposure to quasi-UFP (QUFP, <241 nm), most of which present in the city streets are produced by road traffic, varies greatly depending on the transport mode and route chosen. Proximity to fresh traffic exhaust sources, such as in a car with open windows, on-road cycling, walking downwind of busy roads, or in a subway station contaminated by roadside air, enhances commuter exposure to particles <30 nm in size. In contrast, travelling inside air-conditioned bus or tram offers greater protection to the commuter from high concentrations of fresh exhaust. Ultrafine number size distributions in traffic-contaminated city air typically peak in the size range 30–70 nm, but they can be shifted to finer sizes not only by increased content of fresh proximal exhaust emissions but also by bursts of new particle formation (NPF) events in the city. One such afternoon photochemical nucleation NPF event was identified during our Barcelona study and recognised in different transport modes, including underground in the subway system. The integration of static urban background air monitoring station information with particle number concentration and size distribution data obtained from portable miniaturised SMPS instruments during commuting journeys opens new approaches to investigating city air quality by offering a level of detail not previously available.

Integrated design for underground space environment control of subway stations with atriums using piston ventilation

In subway stations, the piston effect plays an important role in enhancing ventilation to improve subway environment and reduce energy consumption. However, it may induce negative impacts on environmental health and thermal comfort, i.e. air pollution and strong wind. Traditionally, the architecture and ventilation systems are designed separately, and normal ventilation design follows architectural layout. Actually, the architecture design can have a significant influence on the ventilation performance, e.g. airflow pattern. Therefore, this study aims to integrate the design pattern of the architecture with an appropriate ventilation system. A typical subway station of Nanjing (in China) was considered. A dynamic-mesh based computational fluid dynamics (CFD) method was adopted to simulate ventilation performance in the presence of piston effect. Field measurements were conducted to validate the numerical method. New measures were proposed from the perspectives of architectural design to improve the ventilation effect, including enlarging atrium space, adding atrium vents and funnel-shaped exits, etc. The numerical results show that the optimal architectural design could provide a significant improvement towards the airflow environment and ventilation efficiency while avoiding serious air pollution. The proposed integrated-design pattern could further facilitate the creation of an ‘energy-saving’ and ‘healthy’ underground space environment.

A public health concern: emergence of carbapenem-resistant Klebsiella pneumoniae in a public transportation environment.

This study was designed to understand the prevalence of antibiotic-resistant bacteria in the Beijing subway environment and the potential transmission of carbapenem-resistant Enterobacteriaceae in a public transportation environment. Carbapenem-resistant isolates were selected on brain heart infusion agar supplemented with meropenem (0.5 mg/L) and antimicrobial susceptibility testing was conducted using the broth microdilution method. WGS analyses were conducted for 11 Klebsiella pneumoniae isolates to identify resistance genes. The genetic relationships among the isolates were evaluated by MLST and PFGE. We identified 11 carbapenem-resistant K. pneumoniae isolates from the Beijing subway environment. WGS revealed three STs among the 11 isolates, with 9 isolates classified as ST726 and containing a blaNDM-5-carrying IncX3 plasmid. The genetic environment of blaNDM-5 was very similar to that observed in other blaNDM-5-containing clinical isolates. The presence of carbapenem-resistant Enterobacteriaceae in a public transportation environment is concerning and indicates that regular antimicrobial resistance surveillance is urgent and necessary.

Analysis on Alighting and Boarding Movement Laws in Subway Using Modified Social Force Model

This paper presents a multi-agent simulator based on social force model to simulate each passenger’s boarding and alighting behavior both in a train and on a platform seamlessly. Passengers can be divided into three types: to board, alight and stay in train. They have different individual attributes and follow different walking rules. Due to the characteristics of subway environment and passengers' behavior in boarding and alighting, some adjustment and improvement were made to the basic social force model: (1) In some cases during the process of boarding and alighting, the driving force targeting to destination needs to be doubled, and the repulsion force between two agents needs to be reduced. (2) Passengers who stay in the train show quite different movement from the usual pedestrian. They usually want to remain still, unless they are in front of the door. To describe their behaviors, we introduced a tangent detour force. The scope of the interaction between agents is extended and some passengers out of the visual field also should be counted. (3) Divide the repulsive force between an agent and an obstacle into the frontal force and convex corner force. These two forces have different spheres of influence and calculation methods. The agents could exhibit reasonable intelligence and diversity during alighting and boarding.

Environmental and Health Effects of Ventilation in Subway Stations: A Literature Review.

Environmental health in subway stations, a typical type of urban underground space, is becoming increasingly important. Ventilation is the principal measure for optimizing the complex physical environment in a subway station. This paper narratively reviews the environmental and health effects of subway ventilation and discusses the relevant engineering, environmental, and medical aspects in combination. Ventilation exerts a notable dual effect on environmental health in a subway station. On the one hand, ventilation controls temperature, humidity, and indoor air quality to ensure human comfort and health. On the other hand, ventilation also carries the potential risks of spreading air pollutants or fire smoke through the complex wind environment as well as produces continuous noise. Assessment and management of health risks associated with subway ventilation is essential to attain a healthy subway environment. This, however, requires exposure, threshold data, and thereby necessitates more research into long-term effects, and toxicity as well as epidemiological studies. Additionally, more research is needed to further examine the design and maintenance of ventilation systems. An understanding of the pathogenic mechanisms and aerodynamic characteristics of various pollutants can help formulate ventilation strategies to reduce pollutant concentrations. Moreover, current comprehensive underground space development affords a possibility for creating flexible spaces that optimize ventilation efficiency, acoustic comfort, and space perception.

Influence of train arrival characteristics on unorganized ventilation in underground subway station with platform screen doors

Unorganized ventilation significantly increases the energy consumption of subway stations. Many factors affect unorganized ventilation, and its variation is still not clear. This study established a validated network model using Subway Environment Simulation and developed two general scripts to investigate changes in the unorganized ventilation with varying train arrival characteristics, including the train arrival density and arrival time interval for two-side trains. Furthermore, the cooling load caused by the airflow was calculated. The results reveal that the train arrival density changes the superposition of the unorganized ventilation caused by the previous and next pairs of trains, and it also determines the location and state of the existing trains in the tunnel. That affects the unorganized ventilation in the station. The arrival time interval changes the “phase difference” of airflow generated by each side trains. The cooling load caused by unorganized ventilation is much larger than the current perception. Controlling the mechanical ventilation based on the unorganized ventilation rate and optimizing the arrival time interval can reduce the load markedly. Besides, low indoor temperature results in a significant increase in cooling load.

The Performance of an ASHP System Using Waste Air to Recover Heat Energy in a Subway System

In this short communication, we demonstrate that the performance of a typical air source heat pump (ASHP), exploiting a relatively stable air temperature within a subway environment, is high, even during the peak heating months. After a nine-month operational run, the coefficient of performance is demonstrated to be 3.5. The design and installation difficulties are stated together with the lessons learnt following this trial. The actual energy and carbon savings are discussed.

Urine metabolites associated with cardiovascular effects from exposure of size-fractioned particulate matter in a subway environment: A randomized crossover study

BackgroundAmbient particulate matter (PM) is closely associated with morbidity and mortality from cardiovascular disease. Urine metabolites can be used as a non-invasive means to explore biological mechanisms for such associations, yet has not been performed in relation to different sizes of PM. In this randomized crossover study, we used metabolomics approach to explore the urine biomarkers linked with cardiovascular effects after PM exposure in a subway environment. Methods and resultsThirty-nine subjects were exposed to PM for 4 h in subway system, with either a respirator intervention phase (RIP) with facemask and no intervention phase (NIP) in random order with a 2-week washout period. Electrocardiogram (ECG) parameters and ambulatory blood pressure (BP) were monitored during the whole riding period and urine samples were collected for metabolomics analysis. After exposure to PM for 4 h in subway system, 4 urine metabolites in male and 7 urine metabolites in female were screened out by UPLC/Q-TOF MS/MS-based metabolomics approach. Cardiovascular parameters (HRV and HR) predominantly decreased in response to all size-fractions of PM and were more sensitive in response to different size-fractioned PM in males than females. Besides LF/HF, most of the HRV indices decrease induced by the increase of all size-fractioned PM while PM1.0 was found as the most influential one on indicators of cardiovascular effects and urine metabolites both genders. Prolyl-arginine and 8-OHdG were found to have opposing role regards to HRV and HR in male. ConclusionOur data indicated that short-term exposure to PM in a subway environment may increase the risk of cardiovascular disease as well as affect urine metabolites in a size dependent manner (besides PM0.5), and male were more prone to trigger the cardiovascular events than female after exposure to PM; whereas wearing facemask could effectively reduce the adverse effects caused by PM.

Effect of platform subway depth on the presence of Airborne PM2.5, metals, and toxic organic species

PM2.5 that have been related to public health risks, were collected during two seasons with High-Vol samplers in platforms of a Mexican subway station, which interconnects through transfers three lines having different depths. The objective was to study the influence of depth on the PM2.5 concentrations and their species. PM2.5 concentrations in cold-dry and warm-dry seasons presented statistical differences, being in average 57 and 66 μgm-3 respectively, in the shallower line 9; 90 μgm-3 and 111 μgm-3 in line 1; and 104 and 122 μgm-3in the deepest line 7. During the cold-dry season and warm-dry season PM2.5concentrations in the subway environment were respectively up to 3.5 times and up to 5 times greater than in the ambient air. Like PM2.5, metals analyzed with an OES-ICP presented higher concentrations in deeper lines as well as PAHs quantified with CG-MS, which ranged from 4.5 to 11.7 ngm-3. High PM2.5, metals and organic toxic concentrations found in deeper lines of the subway environment represent a risk for commuters endorsing the need for ventilation systems to reduce them. Zn, Pb, V and Ni in subway particles presented the highest solubility in artificial lysosomal fluid suggesting high bioavailability in the lung fluids.

Study on the subway environment induced by moving train using Gaussian distributed momentum source theory method

The application of dynamic mesh method has been extensively applied for simulating piston wind-induced subway environments, e.g. air quality, which is not central processing unit-friendly in calcul...

Effect of stray current on stability of bound chlorides in chloride and sulfate coexistence environment

Destabilization and release of bound chlorides in reinforced concrete structures (RCS) cause accelerated corrosion of steel bars, posing an attendant risk to the durability of the whole structure. This problem is exacerbated by an aggressive environment where chloride and sulfate coexist, and stray current is present, which are commonly observed for RCS built in the subway system. This study tried to simulate the environment of underground track structure by means of intermixing sodium chloride with sodium sulfate and concurrently imposing a stray current. The chloride binding capacity of mortar samples prepared with different water-to-cement (w/c) ratio was examined. Moreover, the effect of current density on the stability of bound chlorides was also investigated. The results showed that the stability of bound chlorides was closely related to the w/c ratio and the current density. In the presence of stray current, the chloride binding capacity of cement mortars was significantly decreased by either a high w/c ratio or a high current density. Interestingly, stray current had a bigger impact on the stability of physically bound chlorides but a much smaller impact on the stability of chemically bound chlorides. X-ray diffraction (XRD) analysis and Thermal gravimetric (TG) and differential thermal gravimetric (DTG) analysis demonstrated that the destabilization of bounded chlorides under stray current and in the presence of sulfates was mainly attributed to the decomposition of the C-S-H gel and the Friedel’s salts. Findings from this research shed new light on the fate of bound chlorides in RCS in complex subway environments.

Aerosol sources in subway environments

Millions of people use rail subway public transport around the world, despite the relatively high particulate matter (PM) concentrations in these underground environments, requiring the identification and quantification of the aerosol source contributions to improve the air quality. An extensive aerosol monitoring campaign was carried out in eleven subway stations in the Barcelona metro system, belonging to seven subway lines. PM2.5 samples were collected during the metro operating hours and chemically analysed to determine major and trace elements, inorganic ions, and total carbon. The chemical compositions of subway components such as brake pads, rail tracks and pantographs were also determined.The mean PM2.5 concentrations varied widely among stations, ranging from 26 µg m−3 to 86 µg m−3. Subway PM2.5 was mainly constituted by Fe2O3 (30–66%), followed by carbonaceous matter (18–37%) for the old stations, while for new stations equipped with Platform Screen Doors (PSD) these percentages go down to 21–44% and 15–30%, respectively. Both the absolute concentrations and the relative abundance of key species differed for each subway station, although with common patterns within a given subway line. This is a result of the different emission chemical profiles in different subway lines (using diverse types of brakes and/or pantographs). The co-emission of different sources poses a problem for their separation by receptor models. Nevertheless, receptor modelling (Positive Matrix Factorization) was applied resulting in ten sources, five of them subway-specific: RailWheel, RailWheel+Brake, Brake_A, Brake_B, Pb. The sum of their contributions accounted for 43–91% of bulk PM2.5 for the old stations and 21–52% for the stations with PSD. The decrease of the activity during the weekends resulted in a decrease (up to 56%) in the subway-specific sources contribution to the –already lower– bulk PM2.5 concentrations compared to weekdays. The health-related elements are mainly apportioned (> 60%) by subway sources.

Use of artificial neural networks for the prediction of time-dependent air speed variation in metro stations

In this study, the time-dependent, induced air speeds at critical sections of underground metro stations are assessed using a novel one-dimensional data-driven approach. For this purpose, three artificial neural networks are used, each trained for the most basic configuration of a single train moving in a single tunnel. The first two are trained to provide the maximum and time averaged values of the induced air speeds while the train is moving inside the approach tunnel or the station. The third one is used to simulate the time-dependent air speed variation during train stoppage and departure. Typical structures of a metro system such as staircases and ventilation shafts are introduced into the solution using simple analytical relations based on loss coefficients. The developed approach is tested using two different metro stations that are currently in operation in Turkey. The selected stations are constructed using different tunneling techniques resulting in different air flow characteristics. The results show that the time variation of the air speed predicted by the developed model is, in general, in good agreement with the results of the Subway Environmental Simulation software, although further studies are necessary to model the acceleration and deceleration of trains more realistically.

Propagation at mmW Band in Metropolitan Railway Tunnels

The next generation of mobile communications, 5G, will provide a wideband network based on microwave and millimeter‐wave (mmW) communication radio links with the goal of fulfilling the strict and severe requirements of the future test cases. In particular, this paper research is focused on mmW bands in metropolitan railway tunnels. For that purpose, a propagation measurement campaign was performed at 24 GHz band in a passenger train on a realist subway environment, and these results were combined with simulations ad hoc for tunnels and a theoretical modal propagation model. A narrowband and a wideband study have been conducted with the aim of obtaining the path loss, fading, power‐delay profile, and angle of arrival, taking into consideration horizontal and vertical polarization in the receiving and transmitting antennas. This validation can be used to design and deploy wideband mobile communication networks at mmW bands in railway scenarios.

Numerical simulation of pollutant transport in soils surrounding subway infrastructure.

With continued urbanization, public transport infrastructure, e.g., subways, is expected to be built in historically industrial areas. To minimize the transfer of volatile organic compounds and metalloids like arsenic from industrial areas into subway environments and reduce their impact on public health, the transport of pollutants in soil was simulated in this study. During numerical simulations of a contaminated site, the pollutant (arsenic) was transported from layers of higher to lower concentration, and concentration changes were particularly evident in the early simulation stages. The pollutant was transported in soil along the direction of groundwater flow and spread from the center to the periphery of the contaminated zone without inputs from pollution sources. After approximately 400days, the concentration of all layers became uniform, with slow decreases occurring over time. The pollutant supply rate had a major influence on the pollutant diffusion distance. When other conditions were kept constant, higher supply rates resulted in longer diffusion distances. The simulation results show that a diaphragm wall of a certain depth can effectively control the diffusion of pollutants in soil. These results can be used to improve environmental assessments and remediation efforts and inform engineering decisions during the construction of urban infrastructure at sites affected by historical pollution.

STESS: Subway thermal environment simulation software

The ongoing city developments in China have resulted in the expansion of the city subway system as well. To provide design and operation guidance for the control system of the environment of subway stations and tunnels, Tsinghua University (Beijing, China) has undertaken a multiyear study of the environment and developed Subway Environment Simulation Software (STESS).The software can simulate the dynamic thermal environment in subways under different environmental control system. It is an effective auxiliary tool for design, operational decisions as well as economic analysis. Compared to Subway Environment Simulation (SES), STESS improves the airflow and underground unsteady heat transfer algorithm. Firstly, STESS adopts MMKP method instead of the four-step Runge-Kutta used in SES to solve unsteady flow to accelerate the convergence. Secondly, two-dimensional mode is used in STESS other than concentric cylinder model in the heat transfer algorithm to adapt to heterogeneous underground environment. And lastly, this software uses the Eigenvalue method to achieve the dynamic simulation of the heat transfer process. Tsinghua University also organized field tests in Beijing and Shanghai and verified the accuracy of STESS. This paper introduces the development history, technical features, program structure and main functions of STESS and presents the experimental validation performed on the software.