Urban Road Tunnel Research Articles

Should We Expect a Disastrous Fire Accident in an Urban Road Tunnel? Literature Data Review and a Case Study for Selected Tunnels in Poland

Urban road tunnels are a reasonable remedy for inconvenience due to congested road traffic. However, they bring specific threats, especially those related to the possibility of fire outbreak. This work is a case study for selected urban road tunnels. Considering tunnel specificity, road traffic intensity, and structure and based on the literature data for vehicle fire probability, the chances of a fire accident were estimated for selected tunnels in Poland. It was shown that low power tunnel fires could be expected in the 10–20-year time horizon. Although such threats cannot be disregarded, tunnel systems are designed to cope with them. The chances of a disastrous fire accident were estimated as well. Such events can occur when an HGV with flammable goods or a tanker are involved. Such accidents are fortunately very rare, but, on the other hand, that is the reason why the available data are scanty and burdened with high uncertainty. Therefore, a discussion on the reliability of the obtained results is also provided.

A fly-wing smoke screen to improve the smoke exhaustion performance of a vertical shaft in road tunnel

A series of numerical simulations were carried out to investigate the effectiveness of a fly-wing smoke screen in improving smoke exhaustion performance in a naturally ventilated urban road tunnel with vertical shafts. The fly-wing smoke screens with different included angles (0°<θ≤180°) were installed under the tunnel ceiling. The numerical results showed that plug-holing was prevented effectively by the fly-wing smoke screen, which stops, gathers, and then guides the smoke to the shaft vent. The velocity field under the tunnel ceiling showed that the optimal included angle with better smoke exhaustion performance was 60°≤θ≤120°. The curve of CO mass flow rate through vertical shaft can be divided into three regions. The best included angle of fly-wing smoke screen is found at 90° with the best smoke exhaustion efficiency. An empirical formula is proposed to describe the exhaustion improvement effectiveness of fly-wing screen. The variation of smoke exhaustion improvement is mainly dominated by the coupling effect of smoke gathering and flow-guidance of the fly-wing smoke screen under different included angles. The practical engineering application of the proposed fly-wing smoke screen in urban tunnels with vertical shaft is also presented. This research offers a basic reference for the design of those naturally ventilated road tunnels with vertical shaft and fly-wing smoke screen.

Modeling for geometry-based massive MIMO V2V channels and analysis of space-time correlation

This paper proposed a three-dimensional dual-spheres confocal ellipsoid geometry-based model for massive MIMO vehicle-to-vehicle (V2V) communication. In this proposed model, the received signal is composed of non-line-of-sight propagation components generated via effective scatterers and line-of-sight propagation components. According to the geometric relationships in the model, the information of angle and distance can be derived, and then the space-time correlation function expression is obtained. To calculate parameters, modified method of equal areas is employed, and the influence on space-time correlation of scatters in different environments is analyzed. Channel characteristics in different scenarios such as highway scenario, urban road scenario and tunnel scenario are compared and studied. Simulation results show that the scatterers distribution and angle information of antenna arrays make a joint contribution on spatial cross-correlation, and moreover, the degree of anisotropy of scatterers and multipath components have distinct impacts on temporal auto-correlation. Compared with the results of 2D model, the proposed 3D model in this paper is more appropriate to characterize V2V communication in various scenarios.

Modelling particle diffusion patterns inside urban road tunnels in Dalian, China, employing annual field measurement

Urban road tunnels have been increasingly constructed to ease traffic congestion and the significant accumulation of particulate matter, posing a potential human health threat. A field measurement over one year in the Lianhuashan, Jiaojinshan, and Shimenshan urban tunnels in Dalian, China was conducted to evaluate particulate pollution levels. A semi-parametric particle diffusion model was then conceived and applied, with the aim of describing the influence of traffic flow, air flow induced by both natural winds and vehicle movements, and other factors, on particle mass concentrations in tunnels. The model was then verified and modified using the measured data. The results showed that PM2.5 mass concentrations in the Lianhuashan and Jiaojinshan tunnels were 29.8 ± 13.8 μg/m3 and 38.7 ± 9.9 μg/m3, respectively, which did not exceed the applicable 24 h averaged World Health Organization (WHO) standard (75 μg/m3). The PM2.5 mass concentrations in the Shimenshan tunnel were 77.2 ± 17.4 μg/m3, slightly exceeding the standard. PM2.5 mass concentrations in the Jiaojinshan and Shimenshan tunnels demonstrated quite clear seasonal patterns, with 36% and 10% higher particle concentrations in winter, respectively, compared with other seasons. The ratios for PM10, PM2.5, and PM1.0 mass concentration to PM0.3 mass concentration were approximately 5, 4, and 3, respectively. A 10 s update frequency for particle mass concentration measurements seemed optimal for model performance. Overall, the results from this study provide fundamental information for predicting particle exposure levels in tunnels and provide useful guidance for the design and operation of their ventilation systems.

Theoretical and numerical study on mass flow rates of smoke exhausted from short vertical shafts in naturally ventilated urban road tunnel fires

The study focuses on the mass flow rate of the buoyancy-driven gases exhausted from the shaft in naturally ventilated urban road tunnel fires. Theoretical analyses and numerical simulations are performed. The model to predict the mass flow rate of the incoming smoke exhausted by the nearest shaft is developed by considering that the smoke is exhausted along the four sides of the shaft separately. Based on the heat balance between the incoming smoke exhausted and the total gas flow exhausted, the model to estimate the total mass flow rate exhausted from the shaft (both smoke and entrained air) is also established. Meanwhile, a series of numerical simulation in a naturally ventilated tunnel considering the heat release rate (HRR), the shaft height, shaft length and width, shaft location was carried out. The simulation results show that the shaft height has a limited contribution to the mass flow rate of the incoming smoke exhausted while a larger shaft cross-sectional area shows a favorable performance in exhausting the smoke. Further, the air entrainment into the shaft increases with both the shaft height and shaft cross-sectional area. Comparisons of the mass flow rates of the incoming smoke and the total mass flow rates exhausted between simple calculations and simulations are made, showing that the simple models perform well. Further, it is found that there exist two regimes for the total mass flow rate corresponding to different smoke modes in the shaft (complete plug-holing, plug-holing and without plug-holing), which is caused by the different driven forces in the shaft. The outcomes of this work could provide some guidance for the design of vertical shaft and smoke control in naturally ventilated tunnel in urban area.

The effect of technical installations on evacuation performance in urban road tunnel fires

Tunnels are separated from the ground by structural linings, and are enclosed and unfamiliar for occupants. In tunnel fires, occupants are faced with a dangerous environment and they need to evacuate. Conveying and obtaining information about the evacuation is the key issue for evacuees. Since tunnels typically have low lighting and little connection outside the tunnel, technical installations are the only approach to deliver information to occupants in order to guide their fast and safe evacuation. This is particularly an issue for urban road tunnels with large occupants’ flow in a large underground space. The present study explores the effect and role of technical installations (alarms, information signs, and lighting) on people’s evacuation performance in urban tunnel fires, through field experiments, questionnaires and interviews. Theory of affordance (sensory affordance, cognitive affordance and functional affordance) is taken into consideration and provides an integral evaluation for technical installations. Technical installations are useful in helping occupants notice the emergency, finding exits and guiding path, and information signs are regarded as the most powerful among those three. Besides, this experiment points out some side effect from alarms and ambiguity of signs which will result in serious consequence potentially. This study leads to guidance on improvement of technical installations on evacuation planning and procedures on urban road tunnels.

Impact on ground-level ozone formation by emission characterization of volatile organic compounds from a flex-fuel light-duty vehicle fleet in a traffic tunnel in Rio de Janeiro, Brazil

The present study aimed to evaluate the contribution of mobile source emissions from, in particular, light-duty vehicles (LDVs) to tropospheric ozone formation in the Rio de Janeiro Metropolitan Area (RJMA), by quantifying the volatile organic compounds (VOCs) in a representative urban road tunnel of the city. The importance of having this type of study in Brazil is because this country has a unique vehicle emission scenario that passenger cars can use different percentages of bioethanol mixed in gasoline. The concentration of speciated VOCs in Reboucas tunnel in Rio de Janeiro, Brazil, was measured in two campaigns, total period of eight weekdays, and the VOC determination was used to calculate the average composition of the emissions of Rio de Janeiro’s LDV fleet. The United States Environmental Protection Agency (US EPA) method TO-15 was applied to determine the concentrations of VOCs C3–C12. It was found that the vehicles circulating through the tunnel were predominantly light-duty flex-fuel cars (99%). The VOC profile was constant in the monitored period. The most abundant compounds were, in order, propane, iso-pentane, n-pentane, propene, and n-butane. In addition, mono-aromatic compounds were found to be the VOC class with the highest ozone-forming potential (OFP), while propene was the main VOC contributor to ozone formation, being responsible for 27% of the troposphere ozone formed by the total VOCs monitored in the present study.

Study on the influence of bypass tunnel angle on gas shunting efficiency of urban road tunnels

In order to analyze the feasibility of setting bypass tunnel in urban highway tunnel for pollutant purification and dust removal, a physical model including main tunnel and bypass tunnel is established based on ICEM and Fluent numerical simulation software. The purpose of this paper is to analyze the influence of the angle between the bypass tunnel and the main tunnel on the velocity field, pressure distribution and the efficiency of air flow from main tunnel to bypass tunnel. The results show that low-speed and low-pressure areas are generated in the main tunnel which is corresponding to the bypass tunnel entrance (short passageway), and vortices are formed. After the tunnel is opened to traffic, this area will become a pollutant accumulation zone. The bypass tunnel shunting efficiency will increase as the angle decreases. In engineering design, under conditions that meet the safety and economics of the project construction, the included angle can be set to the minimum but not less than 30° to achieve the maximum efficiency.

Smoke flow in full-scale urban road tunnel fires with large cross-sectional vertical shafts

In this study, a series of full-scale fire tests are performed in a tunnel with large cross-sectional vertical shafts. The heat release rates and fire locations are considered, and the general smoke development, smoke flow pattern in the shaft, smoke temperature distribution, and smoke front velocity are analysed. It is found that complete plug-holing occurs in the tunnel with large cross-sectional vertical shafts. The smoke flows into the shaft from the bottom sides and spreads out along the shaft sidewalls. The smoke cannot fill the shaft cross-section, even at the shaft outlet. In the early and full-development stages of a fire, a well-stratified smoke layer exists, whereas in the decay stage and after burning out, the visibility significantly reduces. The smoke can be controlled within 80–125 m on each side of the fire source, and it takes approximately 10 min for the visibility to self-recover naturally for common car fires after burning out. The results of the full-scale experiment indicate that the shaft has acceptable performance in smoke control for the test scenario investigated. According to an analysis of the tunnel environment during a common car fire, as well as the evacuation movement, it can be concluded that the occupants can escape safely. The experimental results are used to verify the smoke control performance of the vertical shaft and provide guidance for the design of naturally ventilated tunnels with vertical shafts.

A simple model for predicting the smoke spread length during a fire in a shallow urban road tunnel with roof openings under natural ventilation

When a fire occurs in a road tunnel with roof openings, smoke generated by the fire is exhausted through the roof openings in the ceiling by natural buoyancy of the hot smoke, and as a result, the smoke spread length in the tunnel is limited. In this study, we conduct fire experiments using a 1:10 scale model tunnel with roof openings of a 10% opening ratio, and propose a simple model for predicting the smoke spread length in the tunnel based on the results of the experiments. A constant smoke spread length is both observed in the fire experiments and predicted by the simple model. Sensitivity analysis on the effects of the parameters used in the simple model on smoke spread length clarifies the dominant parameters. Furthermore, we clarify that the smoke spread length is decided by a balance between inertia and buoyancy in the hot smoke flow and the inertia of fresh cold air flow induced by the fire.

Experimental approach to suppress smoke diffusion in sloped road tunnels

In case of a fire in an urban road tunnel with a longitudinal ventilation system, for public safety, it is necessary to ensure that evacuation is initiated at a very early stage. The smoke from the fire can cause breathing difficulties and critically affect evacuees; thus, the smoke should be controlled by means of the ventilation equipment to suppress its diffusion. This paper focuses on the smoke behavior in sloped road tunnels and the airflow velocity required to ensure a safe evacuation environment.

Whole Risk Assessment System and Management System of Urban Road Tunnel Operation Stage

The index system and evaluation method of safety assessment in the operation stage are established to realize the safety risk assessment and management in the operation stage of urban road tunnel. The index scores are obtained from the fuzzy comprehensive evaluation model, and the overall safety risk grade is derived. In view of the index level with an evaluation level greater than or equal to Ⅲ, special risk assessment is conducted, and safety risk solving measures are introduced. A corresponding safety risk management system platform for urban tunnel operation stage is developed on the basis of the results. The results and application of this study have a certain reference value for managing tunnel informatization based on safety risk management.

A theoretical explanation of natural ventilation at roof openings in urban road tunnels

Natural ventilation through openings in the roof of a road tunnel is a green technique that saves energy and greatly improves the air quality inside the tunnel. However, even though multiple tunnels with natural ventilation have been built in China, the theoretical basis for designing and constructing such tunnels is incomplete and there is as yet no uniform and systematic understanding of the natural-ventilation mechanism at the roof openings. Aimed at these problems and based on nearly six years of research and experiments, this paper presents a theoretical explanation of the flow-field characteristics in a road tunnel and the natural ventilation at its roof openings, including (i) the distribution and governing equations for the flow in the tunnel, (ii) the energy governing equation and (iii) the equation governing the natural ventilation at the roof openings. The presented theoretical formulas are consistent with the measured data. The main conclusions are as follows. (1) The airflow in a road tunnel is drag flow resulting from vehicles driving in a restricted space. The flow develops in a bottom-up manner and tends to be stable. The flow velocity is distributed double-logarithmically with height in the tunnel. (2) Moving vehicles are energy sources for the airflow in a road tunnel. Some of the energy transferred from a moving vehicle to the air increases the airflow velocity, while the rest is consumed in turbulence. As the flow develops, the kinetic energy increment decreases gradually and tends to zero, while the energy dissipation decreases gradually and tends to be stable. (3) The air above a road tunnel with roof openings can be sucked into the tunnel by the airflow induced therein by the unidirectional continuous traffic flow. This creates airflow from exterior to interior, but there is no corresponding ‘breathing’ phenomenon. The air inlet velocity at the roof openings differs considerably along the tunnel. It is maximum near the tunnel entrance and decreases gradually along the tunnel, presenting a concave curve.

Study on the Annual Reduction Rate of Vehicle Emission Factors for Carbon Monoxide: A Case Study of Urban Road Tunnels in Shenzhen, China

Environmental pollution and energy conservation in urban tunnels have become important issues that affect the scientific design and sustainable development of urban tunnels. The carbon monoxide (CO) concentration in urban road tunnels is regarded as a direct reflection and a useful tracer of the intensity of anthropogenic transportation activities. Previous studies in recent years have paid more attention to pollutant emission factors, but less to the calculation parameters of ventilation design for tunnels. This paper aims to study a reasonable annual reduction rate of CO base emission factors. Therefore, a detailed field measurement was carried out in the four typical urban road tunnels, Henglongshan Tunnel, Cejiexian Tunnel, Jiuweiling Tunnel, and Dameisha Tunnel in Shenzhen, China, from March 29 to September 16, 2014. Measurement results showed that the traffic flow of the four urban tunnels had been approaching the design value, or even beyond the limit. The average daily air velocities in the four tunnels were all within 5 m/s, whereas the maximum air velocity had exceeded the limit of 10 m/s. The CO concentrations in Henglongshan Tunnel, Cejiexian Tunnel, Jiuweiling Tunnel, and Dameisha Tunnel were 17 ppm, 7 ppm, 39 ppm, and 8 ppm, respectively. Moreover, it was found that the average CO emission factors of Henglongshan Tunnel, Cejiexian Tunnel, Jiuweiling Tunnel, and Dameisha Tunnel were 1.075 g/(km·veh), 1.245 g/(km·veh), 4.154 g/(km·veh), and 1.739 g/(km·veh), respectively. Based on the statistical data, the CO emission factors of mixed traffic and passenger cars decrease by an average of 16.4% and 33.3%, respectively, per year through the regression method and by an average of 17.4% and 29.0%, respectively, per year through the extremum method. Finally, when considering the safety factor of 20%, it is more reasonable for the CO base emission to adopt 4% as an annual reduction rate for ventilation design in urban tunnels.

“Human-Vehicle-Tunnel-Environment” Based Study on Key Issues and Solutions of Operation and Maintenance Risk Evaluation for Urban Road Tunnels

This paper provides analyses of operating environment features of urban tunnels in building, traffic, hydrology, vertical alignment, social environment and examination of key issues in operation and maintenance risk evaluation for urban tunnels: diversity and complexity of evaluation factors; timeliness of evaluation result; uncertainty of rating, etc. Relevant countermeasures are proposed for the above-mentioned key issues, including information collection technology based on the Internet of big data technology and risk dynamic assessment and management platform, etc., to provide a solution path for the real-time, intelligent and informatization of urban tunnel risk management and control.

Investigation on the Time Factor of CO‐Based Emission Factors for Sustainable Development of Urban Tunnels in China

Environmental pollution problems and energy‐saving issues of urban tunnels have increasingly been attracting people’s attention. The paper aims at investigating a reasonable time factor for CO‐based emission factors in the ventilation design of urban road tunnels. The study results show that the prediction curve of CO‐based emission factor for passenger cars consists of two stages. The average reduction rates of Stage I (2004–2010) and Stage II (2010–2030) are 38% and 14% per year, respectively. The CO emission factor series of passenger cars conforms to exponential function distribution. The time factors of CO‐based emission backcalculated from the measured data range from 4.9% to 12.6%, which are 2.4–6.3 times the specified value in the Chinese ventilation specification but slightly smaller than predicted ones. Based on four aspects of predicted results, back analysis results, related references, and engineering applications, it is indicated that the time factor of CO‐based emission factor (2%) in the current ventilation specification is conservative. And when defining 2000 and 2010 as base years, respectively, 4% and 3% can be used as the time factors of CO‐based emission factors respectively for the ventilation design of urban tunnels. This study can provide a reference for ventilation design of urban tunnels in other regions.

A Numerical Study on Parameters Affecting Seismic Behavior of Cut and Cover Tunnel

Underground structures and facilities constitute the underlying and infrastructural part of modern urbanization and are used for a wide range of applications, including urban underground railroad and urban road tunnels, silos etc. Underground structure’s construction method depends on such factors as the ground conditions, the ground water conditions, the tunnel span and the buried depth. The cut and cover method is an engineering technique for underground construction with low buried depth in urban areas. Furthermore, some urban underground facilities have been constructed in areas with risk of seismic activity which be resistant to both static and seismic loads. Therefore, seismic response of such shallow tunnels which are usually constructed by cut and cover method is of great importance and is investigated in this paper. Numerical analyses were performed on a shallow tunnel subjected to S-wave by using FLAC software, and the effects of different parameters are investigated. The maximum forces and bending moments in the tunnel lining during the earthquake motion for two earthquakes i.e., Tabas and Gilroy were compared and it was found that at all levels of maximum acceleration of input motion, seismic forces on tunnel structures during the Tabas earthquake were more critical which is related to the Arias intensity of the input motion. Increasing the buried depth of shallow tunnel and the enlargement of the tunnel span lead to more seismic forces on tunnel structures. Furthermore, with the increasing rigidity of the tunnel to the surrounding soil, additional dynamic forces in the tunnel lining will be more, however the stresses in the tunnel lining are reduced.

Pressure-induced dipole theory and pressure pulsation in shallow urban road tunnels with top vents

Shallow urban road tunnels with top vents represent environmentally friendly and energy-saving technology. To date, four such tunnels are operational in Nanjing, and their intra-tunnel air quality has been widely acclaimed. However, no prescriptive design methods have been developed for this technology. Natural ventilation at the top of the tunnels is caused by the pressure difference inside and outside the top vents. Thus, a prerequisite to the development of scientific design methods for such tunnels is a complete understanding and representation of the pressure wave distribution pattern in the tunnels. Based on an analogy with an electric dipole, we propose a pressure-induced dipole theory and construct an intra-tunnel pressure distribution model. An experimental platform is developed to evaluate the pressure distribution inside tunnels under 6 operational conditions. The results suggest the following. (1) The proposed pressure-induced dipole theory can well describe and explain the pressure wave distribution rules in road tunnels. (2) With a uniform and continuous traffic flow, the real-time pressure on each point in the tunnels demonstrates periodical asymmetrical quasi-sinusoidal pulsation, where the cycle is given as T = (S + L)/v. (3) Periodical pressure pulsation with decaying amplitude exists around the top vents. With large top vents, the pressure exchange between the inside and outside of the tunnels is significant.

Optimization of outdoor design temperature for summer ventilation for undersea road tunnel using field measurement and statistics

Based on the statistics of traffic flow in an urban undersea road tunnel, the temperature, humidity as well as the air velocity were tested. The impact of the temperature difference between the outdoor air temperature during evening peak traffic flow and the ventilation design temperature at 14:00 on ventilation rate was also analyzed in detail. For temperature control of undersea road tunnel, a new method of determining the outdoor design temperature for summer ventilation was proposed. The field measurement and statistical research show the followings: (1) There is a daily cyclical hump for the traffic flow, and the morning and evening traffic peaks are roughly distributed from 7:00 to 9:00 and from 16:00 to 18:00; (2) The air velocity fluctuates between 3.0 and 5.5 m/s; (3) There is a time misfit between the peak time of traffic flow and the time taken for outdoor design temperature for summer ventilation. When carrying out ventilation design of the undersea road tunnel, the outdoor air temperature 1 h after the start of evening traffic peak should be taken as the outdoor design temperature for summer ventilation in order to reduce ventilation rate and energy consumption by more than 10%.

Influence of high humidity and salt-rich spray environment on ventilation effect in urban undersea road tunnel

The urban undersea road tunnels are featured with high frequent traffic congestions and a strict environmental control standard. The internal environment in urban undersea road tunnels is generally controlled by jet fans. The high-humidity, salt-rich spray and acid gas environment in urban undersea road tunnels accelerate the jet fans corrosion, which deteriorates the internal environment and makes the ventilation effect unable to meet the control standards. Detailed examples of pressure drop caused by jet fan corrosion are sparsely available in the publicly available literature. Therefore, this study is to investigate the influence of jet fan corrosion on ventilation effect in urban undersea road tunnel. Based on the Xiamen Xiang’an undersea tunnel, the field measurement of lift produced by jet fan in the tunnel was carried out. Combined with theoretical analysis and Fluent dynamic grid numerical model, the mechanism of reducing lift by jet fan corrosion and the attenuation law of jet fan lift with corrosion time were studied. The results show that salt spray corrosion environment in undersea road tunnel increases surface roughness of the jet fan blades and flow-through components through the effects of accumulation and sedimentation, erosion and corrosion, thereby reducing the lift. After 20 years of operation, the numerical simulated jet fan lift will be reduced by 20.3%, and the ventilation effect will be deteriorate by 20.3% simultaneously. Combined with the field measurement results and the service life of jet fan, the safety factor of ventilation system configuration in undersea tunnel is proposed. Results evidenced that the mechanism of reducing lift by jet fan corrosion in urban undersea road tunnel, which can provide basic data for further research and provide reference for the design of the same type of tunnel ventilation system.