Weichen Liao

Measuring the steady state of pedestrian flow in bottleneck experiments

Experiments with pedestrians could depend strongly on initial conditions. Comparisons of the results of such experiments require to distinguish carefully between transient state and steady state. Thus a modified version of the Cumulative Sum Control Chart algorithm is proposed to robustly detect steady states from density and speed time series of bottleneck experiments. The threshold of the detection parameter in the algorithm is calibrated using an autoregressive model. Comparing the detected steady states with manually selected ones, the modified algorithm gives robust and reproducible results. For the applications, three groups of bottleneck experiments are analysed and the steady states are detected. The results reconfirm that the specific flow is constant as bottleneck width changes. Moreover, we proposed a criterion to judge the difference between the flows in all states and in steady states, which is the ratio of pedestrian number to bottleneck width. The critical value of the ratio is found to be approximately 115 persons/m. This conclusion applies not only for the analysis of existing bottleneck experiments but also for the design of new bottleneck experiments and the validation of evacuation models. Furthermore, the range of steady state in time series of pedestrian characteristics could be effectively controlled by adjusting the value of the ratio.

Understanding human queuing behaviour at exits: an empirical study

The choice of the exit to egress from a facility plays a fundamental role in pedestrian modelling and simulation. Yet, empirical evidence for backing up simulation is scarce. In this contribution, we present three new groups of experiments that we conducted in different geometries. We varied parameters such as the width of the doors, the initial location and number of pedestrians which in turn affected their perception of the environment. We extracted and analysed relevant indicators such as distance to the exits and density levels. The results put in evidence the fact that pedestrians use time-dependent information to optimize their exit choice, and that, in congested states, a load balancing over the exits occurs. We propose a minimal modelling approach that covers those situations, especially the cases where the geometry does not show a symmetrical configuration. Most of the models try to achieve the load balancing by simulating the system and solving optimization problems. We show statistically and by simulation that a linear model based on the distance to the exits and the density levels around the exit can be an efficient dynamical alternative.

Validation of FDS+Evac for pedestrian simulations in wide bottlenecks

In this study, the reliability of FDS+Evac (FDS 6.0.1, Evac 2.4.1) is investigated by a series of well-controlled laboratory experiments. The parameters controlling the free speed and the anisotropy of social force between pedestrians are calibrated based on the experimental values. With the adjusted values of the parameters, FDS+Evac is able to reproduce the experimental process with respect to the flow through the bottleneck. However, other pedestrian characteristics in the simulations do not match with those in the experiments. This study shows that the validation of FDS+Evac should not only consider single pedestrian characteristics. More careful calibration of parameters and comprehensive analysis are necessary before FDS+Evac is used for security-related applications in general.

A generalized validation procedure for pedestrian models

Abstract Pedestrian models need to be validated before being applied to real-life planning. Thus, the validation of these models is worthy of special investigation. In this work, we perform two validation exercises with the pedestrian models named FDS+Evac and JuPedSim based on a well-controlled pedestrian experiment. A comprehensive combination of multiple characteristics is used to enhance the reliability of validation results, including model stability, pedestrian flow, time series of density and velocity, spatiotemporal profiles and pedestrian trajectories. The results show that both FDS+Evac and JuPedSim have weaknesses in reproducing full pedestrian characteristics realistically. Our validation exercises illustrate that single characteristic is not enough to guarantee a reliable validation result and a comprehensive combination of multiple characteristics is necessary. This work demonstrates the defects in most of existing validation of pedestrian models and presents a general validation procedure for pedestrian models in future research.

Detection of Steady State in Pedestrian Experiments

Initial conditions could have strong influences on the dynamics of pedestrian experiments. Thus, a careful differentiation between transient state and steady state is important and necessary for a thorough study. In this contribution a modified CUSUM algorithm is proposed to automatically detect steady state from time series of pedestrian experiments. Major modifications on the statistics include introducing a step function to enhance the sensitivity, adding a boundary to limit the increase, and simplifying the calculation to improve the computational efficiency. Furthermore, the threshold of the detection parameter is calibrated using an autoregressive process. By testing the robustness, the modified CUSUM algorithm is able to reproduce identical steady state with different references. Its application well contributes to accurate analysis and reliable comparison of experimental results.