Number Of Pedestrians Research Articles

Simulating crowd behaviour combining both microscopic and macroscopic rules

We propose a new method for simulating pedestrian crowd movement in a virtual environment. A crowd consists of groups of different number of people with different attributes such as gender, age, position, velocity, and energy. Each group has its own intention used to generate a trajectory for each pedestrian navigating in the virtual environment. Additionally, an agent-based model is introduced to simulate pedestrian behaviours in the groups, where various steering behaviours are introduced and combined into a single steering force to allow pedestrians in each group to walk toward their destination point. Based on the proposed method, every single pedestrian in each group can continuously adjust their attributes. Moreover, pedestrians optimize their path independently toward the desired goals, while avoiding obstacles and other pedestrians in the scene. This method takes into account the safety-space around each pedestrian to avoid collisions among pedestrians. The proposed method was implemented for several simulation scenarios under various conditions for a wide range of different parameters. Statistical analysis is carried out to evaluate the performance of the proposed method for simulating the crowd movement in the virtual environment. Results indicate that our method can generate each pedestrian’s trajectories in each group independently to reach several goal points within a reasonable computational time. Moreover, the obtained results reveal that the mean value of the computational time is not increased significantly with the increasing of the number of pedestrians in the crowd.

Kinematics of sea star legged locomotion.

Sea stars have slower crawling and faster bouncing gaits. Both speed and oscillation amplitude increase during the transition from crawling to oscillating. In the bouncy gait, oscillating vertical velocities precede oscillating horizontal velocities by 90 deg, as reflected by clockwise circular hodographs. Potential energy precedes horizontal kinetic energy by 9.6 deg and so they are nearly in phase. These phase relationships resemble terrestrial running gaits, except that podia are always on the ground. Kinetic and potential energy scale with body mass as Mb 1.1, with the change in kinetic energy consistently two orders of magnitude less, indicating that efficient exchange is not feasible. Frequency of the bouncy gait scales with Mb-0.14, which is similar to continuously running vertebrates and indicates that gravitational forces are important. This scaling differs from the Hill model, in which scaling of muscle forces determine frequency. We propose a simple torque-stabilized inverted pendulum (TS-IP) model to conceptualize the dynamics of this gait. The TS-IP model incorporates mathematics equivalent to an angular spring, but implemented by a nearly constant upward force generated by the podia in each step. That upward force is just larger than the force required to sustain the underwater weight of the sea star. Even though the bouncy gait is the rapid gait for these sea stars, the pace of movement is still very slow. In fact, the observed Froude numbers (10-2 to 10-3) are much lower than those typical of vertebrate locomotion and are as low or lower than those reported for slow-walking fruit flies, which are the lowest values for pedestrian Froude numbers of which we are aware.

Glass Suspension Footbridge: Human-Induced Vibration, Serviceability Evaluation, and Vibration Mitigation

Glass suspension footbridges or glass-bottomed suspension footbridges, such as the Zhangjiajie Grand Canyon Glass Bridge in China, are increasingly constructed in scenic regions as tourist attractions due to the glass-bottomed and transparent characteristics. Being installed in the second phase as a constant load, the glass deck is not designed to participate in the load bearing of the whole structure and thus the structure requires larger load-bearing capacity from other parts and a slightly different load-bearing system. More importantly, the glass deck weakens structural integrity and results in slightly smaller structural stiffness, which may result in globally lower natural frequencies. These structures may inevitably be more sensitive to the pedestrian-induced excitations. This paper investigates the human-induced vibrations of a typical glass suspension footbridge in China. The investigations are first performed based on intensive parametric studies. Except for the boundary conditions, the interlayers of glass, the vertical rise–span ratio and the axial stiffness of main cables, other governing parameters of the modal parameters for this type of structures are also identified, including the pavement load of the bridge deck system, the central buckle, and the prestress of wind-resistant cables. It may guide designers to take effective measures to improve the dynamic behavior of this type of structure. Next, the vibration serviceability assessments were performed based on different standards and guidelines such as the UK National Annex (NA) to Eurocode 1 (2008), the Bro2004 specification of Sweden, the HiVoSS guideline, and the ISO standard. Comparisons show that the UK NA to Eurocode 1, the HiVoSS guideline, and the ISO standard are more suitable for the vibration serviceability evaluations. These three codes consider the pedestrian-induced vibrations in both lateral and vertical directions and also consider both a small number of pedestrians and crowd-induced loads with different densities. Furthermore, comfort limits are not defined by only one limiting value but sorted into different levels. This may provide reference for the vibration serviceability evaluations of the other glass suspension footbridges. The assessments also show that changing the structural parameters can only partially reduce vibration levels and may result in different modal parameters to dominate the vibration responses. Thus, they recommend taking vibration mitigation measures to improve the vibration serviceability and suggest performing careful response calculations to ensure the effectiveness of vibration serviceability design if via changing the structural parameters. Finally, tuned mass dampers (TMDs) are installed to the structure. The results show that the popular TMD may effectively reduce the vibration levels.

How do humans impact yellow-bellied marmots? An integrative analysis

While many studies document specific human impacts on the behaviour and physiological responses of wildlife to humans, most have focused on these responses independently and over relatively short periods of time. To address this, we studied a suite of responses in yellow-bellied marmots (Marmota flaviventer) in two distinct years, 9 years apart. We first quantified the rate that vehicles, pedestrians, and bicycles passed marmot colonies, focusing on two years (2009 and 2018) to determine how, if any of these relationships changed over time. We then asked whether these disturbances were associated with marmot physiological responses including neutrophil-lymphocyte ratios (NLR), and faecal glucocorticoid metabolites levels (FGM), as well as behavioural responses including flight initiation distance (FID) and the time marmots allocated to foraging, and finally a key fitness correlate—the rate of mass gain. We found that the number of vehicles and pedestrians passing within 300 m of a marmot colony stayed relatively constant between years, while there was variation in bicycles passing by marmot colonies. Despite similar length in growing seasons, marmots at colonies that had higher disturbance gained mass more rapidly in 2018 than in 2009. By examining a suite of physiological, behavioural, and key fitness correlates, and how they changed, our findings are consistent with the hypothesis that marmots became more tolerant of human disturbances over time. This provides promise for this population in dealing with inevitable increases in eco- and nature-based tourism.

Factors Influencing Fatalities or Severe Injuries to Pedestrians Lying on the Road in Japan: Nationwide Police Database Study.

To help reduce the number of pedestrians lying on the road suffering fatal or severe injuries as a result of vehicle collisions, we investigated the influencing factors. We conducted an analysis of the records of the Institute for Traffic Accident Research and Data Analysis Japan between 2012 and 2018; we found that 2452 pedestrians lying on the road were involved in collisions (797 fatalities, 784 severely injured, 871 mildly injured). Multivariate logistic regression analysis identified the following as major factors that positively influenced the fatalities: head or neck injuries (odds ratio [OR], 90.221); trunk injuries (OR, 71.040); trucks as offending vehicle (OR, 2.741); collision velocity of 10–20 km/h (OR, 31.794), 20–30 km/h (OR, 2.982), 30–40 km/h (OR, 8.394), 40–50 km/h (OR, 16.831), and >50 km/h (OR, 18.639); and hit-and-run cases (OR, 1.967). The following had a positive influence on severe injuries: trunk injuries (OR, 4.060); collision velocity of 10–20 km/h (OR, 2.540), 20–30 km/h (OR, 3.700), 30–40 km/h (OR, 5.297), 40–50 km/h (OR, 5.719), and ≥50 km/h (OR, 5.244); and hit-and-run cases (OR, 2.628). Decreasing the collision velocity, avoiding collisions to the head and neck or trunk, and preventing hit-and-run cases would be effective in reducing fatal or severe injuries to pedestrians lying on the road.

Simulation of dispersion effects by considering interactions of pedestrians and bicyclists using an agent space model

As the number of bicyclists in urban areas continues to increase, the need to realistically model the movement and interactions of bicyclists in mixed urban traffic is rapidly gaining importance. Therefore, this paper presents an agent space model (ASM) to elucidate the movements of bicyclists and pedestrians on shared roads. The ASM model, via simulation, particularly illustrates the dispersion phenomenon observed for non-motorized road users. The mutual interactions and diverse bicyclist and pedestrian properties were also incorporated into this model. The mutual interactions were realised through agent spaces of different sizes in conflict and overtaking behaviours for the following combinations: bicyclist-to-pedestrian, bicyclist-to-bicyclist, pedestrian-to-bicyclist, and pedestrian-to-pedestrian, which were obtained through experiments. The hypothesis test indicated that different agent spaces exist for different types of interactions. The experimental data were used to obtain several variables that describe the elements of road user agent spaces, including longitudinal and lateral distances and the dynamic relationship between the longitudinal distance and speed. The simulation results indicated that with an increase in the number of pedestrians, the maximum capacity decreased and the dispersion degree increased. The following psychological and physiological factors affect the degree of dispersion of bicyclists: travelling speed, reaction time, intensity, probability of selecting the head-on direction, and probability of selecting the right-hand direction. In addition, lane formation was observed in all simulations. The results also demonstrated that dedicated bicycle lanes will significantly reduce the dispersion degree. Moreover, the safety and efficiency effects of different forms of bicycle lanes were analysed from the perspective of the degree of dispersion. The simulation results can provide specific guidelines for understanding the causes of phenomena such as dispersion and lane formation, as well as for studying the traffic dynamics, effects of dedicated bicycle lanes, and macroscopic characteristics according to different bicyclist-pedestrian ratios.

Evaluation of Urban Design Qualities across Five Urban Typologies in Hanoi

Urban design has been shown to play a vital role in promoting the health and wellbeing of urban citizens. However, studies of microscale urban design are underrepresented in comparison with macroscale urban design, especially from low- and middle-income countries in Asia, where urban forms are traditionally compact, complex and with multiple layers and varied urban typologies. The study evaluated microscale urban design qualities of streets (n = 40) across five urban typologies in Hanoi—a typical city in a low- and middle-income country in Asia. The study found that urban typologies and their characteristics have particular impacts on urban design qualities. Old and high-density urban typologies tend to report higher urban design qualities than modern and low-density typologies. Urban design qualities are also significantly associated with the number of pedestrians on the streets. Compared to Western cities, the urban design qualities in Hanoi are substantially different, especially in terms of imageability and complexity, reflecting the differences in urban design and cultural context between cities from various regions. Overall, the study contributes to our understanding of urban design circumstances in Hanoi, providing policymakers, planners, urban designers and architects with important insights for sustainable urban design policies, strategies and interventions.

Emergency Planning for UAV-Controlled Crowd Evacuations

One of the most challenging problems during disasters involving crowds is pedestrian evacuation. It is very important in such situations to improve survival rates by getting all or most of the people out in the shortest possible time. Technological intervention through augmenting the evacuation process using an unmanned aerial vehicle (UAV) exhibits great potential in improving survival rates, but the exploration of this method is still in its infancy. Therefore, this study explores the potential of utilizing UAVs for crowd management during emergency evacuations. We conducted a rigorous study, using a simulation model featuring four UAVs and differing numbers of pedestrians, with use of two UAV guidance approaches: partial guidance and full guidance. The experimental results suggest that exploiting UAVs in crowd evacuation and following the partial guidance approach can lead to a more efficient evacuation process.

Cities and infectious diseases: Assessing the exposure of pedestrians to virus transmission along city streets

As cities resume life in public space, they face the difficult task of retaining outdoor activity while decreasing exposure to airborne viruses, such as the novel coronavirus. Even though the transmission risk is higher in indoor spaces, recent evidence suggests that physical contact outdoors also contributes to an increased virus exposure. Given that streets constitute the largest percentage of public space in cities, there is an increasing need to prioritise their use to minimise transmission risk. However, city officials currently lack the assessment tools to achieve this. This article evaluates the extent to which street segments are associated with spatiotemporal variations of potential exposures of pedestrians to virus transmission. We develop a multi-component risk score that considers both urban form and human activity along streets over time, including (a) an assessment of pedestrian infrastructure according to the average width of pavements, (b) a measure of accessibility for each street based on its position in the street network, (c) an activity exposure score that identifies places along streets where exposure could be higher and (d) an estimate of the number of pedestrians that will pass through each street during weekdays and weekends. We use Amsterdam in the Netherlands as a case study to illustrate how our score could be used to assess the exposure of pedestrians to virus transmission along streets. Our approach can be replicated in other cities facing a similar challenge of bringing life back to the streets while minimising transmission risks.

Vibration serviceability of suspended floor: Full-scale experimental study and assessment

The suspended floor is a relatively new form of floor system in the suspended structure. Owing to the special boundary condition where the whole floor is lifted by cables rather than supported by columns or walls, the suspended floor is flexible and may face the issue of vibration serviceability. In this study, a composite floor lifted by carbon fiber-reinforced polymer (CFRP) cables used for small-scale exhibitions was designed and constructed, and field measurements were conducted to study dynamic characteristics and human-induced vibration serviceability of the suspended floor. The dynamic characteristics test using the natural excitation technique was conducted first, and the fundamental frequency of the floor was determined as 5.08 Hz. Then, the effects of pedestrian number and weight, walking frequency and route, and jumping point and frequency were discussed in the human-induced vibration test. Test results indicated that floor vibration responses increased with the pedestrian number, and increased as the jumping (walking) frequency approached the floor’s fundamental frequency. Higher vibration responses were obtained when the human-induced vibration was exerted on positions with less vertical vibration constraints. Vibration serviceability assessment using peak acceleration and root mean square (RMS) acceleration methods neglecting the effect of vibration duration show that the floor can meet the requirement in public places without excitations like walking at high frequency or rhythmic jumping, whereas vibration dose value/ estimated vibration dose value (VDV/eVDV) methods considering vibration duration tend to give a better comment. This study provides a fundamental basis to fill the lack of research on the vibration serviceability of the suspended floor.

PEDESTRIAN DYNAMICS IN SINGLE-FILE MOVEMENT UNDER BACKGROUND MUSIC WITH DIFFERENT TEMPOS

Large crowds are challenging the comfort and safety level of big cities, while music may be a potential method to improve pedestrian flow. This paper focuses on the influence of different tempos and types of background music on pedestrian dynamics. Three tempos (90[Formula: see text]beats/min (BPM), 120[Formula: see text]BPM and 150[Formula: see text]BPM) and two types (pure music and metronome stimuli) of music are considered. It is found that more frequent stop-and-go behaviors emerge with rhythms. Compared with that under a low tempo (90[Formula: see text]BPM) of rhythm condition, stopping is more frequent with a high tempo one (120[Formula: see text]BPM or 150[Formula: see text]BPM). The number of stopping pedestrians per unit time increases 68.57%, 376.00%, 298.29%, 224.00%, 438.29% and 393.71% with 90 BPM, 120[Formula: see text]BPM and 150[Formula: see text]BPM music, 90[Formula: see text]BPM, 120[Formula: see text]BPM and 150[Formula: see text]BPM metronome, compared with that without any rhythm, respectively. The velocity and flow are lower, and higher local densities appear with background music. The step frequency at high density with rhythms ([Formula: see text], [Formula: see text] and [Formula: see text][Formula: see text]Hz for 90[Formula: see text]BPM, 120[Formula: see text]BPM and 150[Formula: see text]BPM music; [Formula: see text], [Formula: see text] and [Formula: see text][Formula: see text]Hz for 90[Formula: see text]BPM, 120[Formula: see text]BPM and 150[Formula: see text]BPM metronome) is lower than that without any rhythm ([Formula: see text][Formula: see text]Hz). Pedestrians need more time to avoid collisions and to step under background music conditions, because they are influenced by the music and not fully focusing on walking. As a result, step frequency decreases and stopping behavior is more frequent. This in turn leads to the decrease of the velocity and flow and the emergence of higher local densities. Our study will be helpful for understanding the effect of background music on pedestrian dynamics.

Deep deterministic policy gradient algorithm for crowd-evacuation path planning

In existing evacuation methods, the large number of pedestrians and the complex environment will affect the efficiency of evacuation. Therefore, we propose a hierarchical evacuation method based on multi-agent deep reinforcement learning (MADRL) to solve the above problem. First, we use a two-level evacuation mechanism to guide evacuations, the crowd is divided into leaders and followers. Second, in the upper level, leaders perform path planning to guide the evacuation. To obtain the best evacuation path, we propose the efficient multi-agent deep deterministic policy gradient (E-MADDPG) algorithm for crowd-evacuation path planning. E-MADDPG algorithm combines learning curves to improve the fixed experience pool of MADDPG algorithm and uses high-priority experience playback strategy to improve the sampling strategy. The improvement increases the learning efficiency of the algorithm. Meanwhile we extract pedestrian motion trajectories from real motion videos to reduce the state space of algorithm. Third, in the bottom layer, followers use the relative velocity obstacle (RVO) algorithm to avoid collisions and follow leaders to evacuate. Finally, experimental results illustrate that the E-MADDPG algorithm can improve path planning efficiency, while the proposed method can improve the efficiency of crowd evacuation.

Why are convenience stores clustered? The reasons behind the clustering of similar shops and the effect of increased competition

Similar stores, when clustered in urban locations, often close down; many scholars have explained this phenomenon using Hotelling’s theory. However, empirically, several studies have found that competition between rivals causes stores to move away from each other, exhibiting a repulsive force. By contrast, other studies insist that customers strongly drive the agglomeration of retail rivals. This study chooses convenience stores as an experimental subject to investigate why similar shops cluster in an area and to assess the results of increasing levels of competition. By combining various types of big-data sources including convenience stores’ revenues, diverse consumer factors, and built environments, this study found that retail shops cluster to earn revenue by exploiting the consumer purchasing capacity in an area. This benefit, however, disappears when the competition increases beyond a certain threshold. By controlling for the numbers of pedestrians, residents, and employees, this study is the first to explain why similar shops cluster in urban districts and to show the limitations of retail rivals’ clustering.

Investigation of Pedestrian Crossing Behavior at Crossing Facilities in India

Pedestrians are one of the most vulnerable road users, yet requisite attention has not been given to their safety especially in developing countries. Every year large numbers of pedestrians are killed in road crashes in India, and many of them die while crossing the roads. The main aim of this paper is to investigate the crossing behavior of pedestrians & to enhance road safety. The survey was conducted on 1423 participants. Factor analysis was carried out, which divided the pedestrian behaviors into five factors, namely: violation, lapse, error, risk, and infrastructure. Mann Whitney U test, Kruskal Wallis H test and post hoc test (Dunn's test with Bonferroni correction) were conducted to find the correlation between pedestrians' demographic features and behavioral factors. The results showed that the behavioral patterns like violations, lapses and risks are differentiated by gender. Men made statistically more violations, lapses and took more risks than female road users. Pedestrians from the low-income group, many of whom are devoid of formal education, showed more violations and risk-taking behavior compared to those from the higher-income group. Similarly, old road users and those coming from the higher-income group were found to be more concerned about the lack of pedestrian facilities.

PERSEPSI PEJALAN KAKI TERHADAP TROTOAR DI LAPANGAN MERDEKA KOTA MEDAN

Merdeka Square is one of the icons of Medan City which is continously visited by communities of Medan City or immigrant communities because Medan City is the capital of North Sumatera Province with a high complexity of activities in it. Improvements to the road transportation system facilities, especially sidewalk facilites, are important because the purpose of implementing sidewalks is as a special pedestrian lane with security and safety guarantees against traffic accidents.
 This study aims to look at people’s perceptions as the main users of sidewalk facilities so that they can encourage people to carry out walking activities as a basic moda of transportation.
 This research was conducted with a quantitative approach with accidental sampling method, namely primary data is the result of direct interviews in the field to the public using sidewalk facilities at Merdeka Square, Medan City.
 Based on the result of the analysis conducted on the results of the interview, it was found that the community as users of the sidewalks were not satisfied with the existing sidewalks facilities. So this study aims to provide input in order to improve sidewalk facilities that provide comfort and safety values for pedestrians in order to encourage and increase the number of pedestrians, especially at Merdeka Square, Medan City.

Research on Path Planning Algorithm for Crowd Evacuation

In recent years, crowded stampede incidents have occurred frequently, resulting in more and more serious losses. The common cause of such incidents is that when large-scale populations gather in a limited area, the population is highly unstable. In emergency situations, only when the crowd reaches the safe exit as soon as possible within a limited evacuation time to complete evacuation can the loss and casualties be effectively reduced. Therefore, the safety evacuation management of people in public places in emergencies has become a hot topic in the field of public security. Based on the analysis of the factors affecting the crowd path selection, this paper proposes an improved path-planning algorithm based on BEME (Balanced Evacuation for Multiple Exits). And pedestrian evacuation simulation is carried out in multi-exit symmetrical facilities. First, this paper optimizes the update method of the GSDL list in the BEME algorithm as the basis for evacuating pedestrians to choose an exit. Second, the collision between pedestrians is solved by defining the movement rule and collision avoidance strategy. Finally, the algorithm is compared with BEME and traditional path-planning algorithms. The results show that the algorithm can further shorten the global evacuation distance of the symmetrical evacuation scene, effectively balance the number of pedestrians at each exit and reduce the evacuation time. In addition, this improved algorithm uses a collision avoidance strategy to solve the collision and congestion problems in path planning, which helps to maximize evacuation efficiency. Whether the setting of the scene or the setting of the exit, all studies are based on symmetric implementation. This is more in line with the crowd evacuation in the real scene, making the experimental results more meaningful.

Emergency evacuation from multi-exits rooms in the presence of obstacles

To facilitate emergency evacuation, it is essential and important to investigate how system dynamics govern collective behaviors of pedestrians in panic. Although it has already been pointed out that appropriate arrangement of obstacles in a single-exit room can substantially improve evacuation efficiency, whether this conclusion can be carried over to multi-exits scenario still remains puzzling. Motivated by this, we propose an improved social force model to study the influence of the total number of pedestrians, their desired velocity and the specific locations of obstacles on evacuation efficiency for multi-exits configurations. Simulation results show that evacuation efficiency sensitively depends on the arrangement of obstacles. Specifically, there exists an optimal location for the obstacle where the total evacuation time is minimized, but not all the locations have a favorable impact on evacuation. This conclusion also holds for the dependence of evacuation efficiency on obstacles length. More importantly, the effect of obstacles, irrespective of being positive or negative, can be enhanced by increasing the number of pedestrians or the desired velocity. This work may shed some light on the drawing up of emergency scheme for multi-exits public-gathering places like stadiums and shopping malls.

Intelligent Mobility in the City: The Influence of System and Context Factors on Drivers’ Takeover Willingness and Trust in Automated Vehicles

Automated driving in urban environments not only has the potential to improve traffic flow and heighten driver comfort but also to increase traffic safety, particularly for vulnerable road users such as pedestrians. For these benefits to take effect, drivers need to trust and use automated vehicles. This decision is influenced by both system and context factors. However, it is not yet clear how these factors interact with each other, especially for automated driving in city scenarios with crossing pedestrians. Therefore, we conducted an online experiment in which participants (N= 68) experienced short automated rides from the driver’s perspective through an urban environment. In each of the presented videos, a pedestrian crossed the street in front of the automated vehicle while system and context factors were varied: 1) the crossing pedestrian’s intention was either visualized correctly (as crossing) or incorrectly (visualization missing) by the automated vehicle (system factor), 2) the pedestrian was either distracted by using a smartphone while crossing or not (context factor), and 3) the scenario was either more or less complex depending on the number of other vehicles and pedestrians being present (context factor). In situations with a system malfunction where the crossing pedestrian’s intention was not visualized, participants perceived the situation as more critical, had less trust in the automated system, and a higher willingness to take over control regardless of any context factors. However, when the system worked correctly, the crossing pedestrian’s smartphone usage came into play, especially in the less complex scenario. Participants perceived situations with a distracted pedestrian as more critical, trusted the system less, indicated a higher willingness to take over control, and were more uncertain about their decision. As this study demonstrates the influence of distracted pedestrians, more research is needed on context factors and their inclusion in the design of interfaces to keep drivers informed during automated driving in urban environments.

Traffic optimization design of The Intersection of Zhan Qian Road and Min Zhu Zhong Road in Jiaozuo City

In recent years, my country’s road infrastructure has been vigorously constructed, urban road network density has increased, and road intersections have also been formed. There are more and more T-shaped intersections. Such intersections often have the characteristics of serious traffic intertwining and difficult traffic organization. Opposite the intersection of Zhan Qian Road and Min Zhu Zhong Road is the railway station. A large number of pedestrians have to pass through the intersection at rush hour or when the train arrives at the station. This road has a lot of people and a large number of non-motorized vehicles. The signal lights at the intersection are not perfect, and the traffic demand is large. In this paper, based on the current signal timing plan and the current status of the crosswalk at the intersection, based on the actual current data survey and service level analysis, the optimization design of the intersection signal timing plan and the crosswalk width optimization are completed. The results showed that the average delay at the intersection was improved by nearly 21 seconds, and the crosswalk lengths at the east entrance, west entrance and north entrance were optimized to 2.5m, 2.4m and 2.6m, respectively. Improved road capacity and reduced vehicle delays.

Uncertainty-based approaches for the lateral vibration serviceability assessment of slender footbridges

Slender footbridges with long spans and light materials may lead to serviceability problems in lateral vibrations due to walking pedestrians. The phenomenon, known as the “lock-in effect” occurs when the number of pedestrians on the footbridge reaches the “critical number”. Considering the mode of vibration in which the instability is more likely to develop, the footbridge response depends on the structural natural frequency and modal damping ratio. These parameters may not have a fixed value during the footbridge overall life cycle due to environmental and operational changes. Therefore, lateral vibration serviceability procedures should include the uncertainty in the footbridge modal parameters in the most simple and applicable way, as the dynamic response of slender footbridges is very sensitive to these uncertainties.Hence, this paper proposes a simple approach, useful for practical engineering applications, to assess the lateral vibration serviceability of slender footbridges, considering the uncertainties in natural frequency and modal damping ratio. The uncertainty is considered by two approaches: probability theory and possibility theory (fuzzy sets). As a result, the study allows checking the vibration serviceability criteria over a range of levels of uncertainty, suggesting that the external factors that affect the modal parameters are more significant when the crowd density exceeds the critical number. The study also shows the simplicity and effectiveness of the possibility theory to deal with the uncertainty in modal parameters, although for similar level of uncertainty, the dynamic response is slightly higher than using the probability theory. Finally, the proposal is applied in two real footbridges, showing a good agreement with the experimental data.