Omid Ejtemai

Modeling Pedestrian Crowd Exit Choice Through Combining Sources of Stated Preference Data

One crucial aspect of pedestrian behavior when a facility is being evacuated is exit selection. This phenomenon, however, is difficult to capture. Recording revealed choices as the exact situations or moments in which individuals make or change their subconscious exit decisions when evacuating a place is highly ambiguous. The approach in which stated choice data are collected offers an appealing solution to tackle the problem. For the underlying factors that influence peoples exit decisions to be examined, two types of stated preference (SP) data were collected and pooled: traditional stated preference data and stated preference–off–revealed preference (RP) data. The latter is from the state-of-the-art class of stated choice methods that design experiments with reference to an alternative in an individuals actual choice set. The nested logit trick model and a customized version of the generalized mixed multinomial logit model were applied to estimate the difference in variance scale of the two sectors of data and to quantify the relative contribution of the factors of distance, density, visibility, and herding behavior to exit decisions. Results showed that the SP-off-RP method, compared with the classical SP method, led to lower variance for random noise by a small margin. Compared with the nested logit trick method, the generalized mixed multinomial logit approach allowed researchers to consider more behavioral dimensions of the problem as well as accommodate the difference in scale of variance, including heterogeneity in utility weights and utility scale of individuals, correlation between alternatives, correlation of unobserved utility factors over time, and correlation between utility coefficients.

Pedestrian Walking Characteristics Through Angled Corridors: An Experimental Study

Understanding pedestrian walking characteristics is important for the planning and design of mass gathering places for day-to-day activities as well as for emergency evacuations. The optimization of architectural designs and properly managing crowds at public buildings and the built environment is essential to ensure the safety and efficiency of crowd dynamics. Most previous empirical and theoretical studies highlight the behavior of a crowd as a whole system (macroscopic behavior) or interpersonal microscopic interactions within the crowd. A major gap in the knowledge is that no sufficient research has been carried out to examine solo walking characteristics, particularly when individual pedestrians interact with complex geometries such as turning. Whether the existing mathematical or simulation models can accurately reflect the characteristics related to solo human walking characteristics in these conditions is questionable. A series of experiments was conducted to understand the solo walking characteristics of individuals walking through angled corridors at different speeds. Initial results are discussed in detail. Results suggest that an individual tends to reduce speeds within a fixed region on the angled path and that the dimensions of this region are independent of turning angle but dependent on the individuals desired speed. These findings are important for the calibration of parameters or behavioral rules for microscopic pedestrian models.

Elevated Desired Speed and Change in Desired Direction: Effects on Collective Pedestrian Flow Characteristics

Microscopic pedestrian simulation tools have gained increased attention and popularity in recent years. These are essential tools in planning and designing crowd-gathering places and public buildings. For increased reliability of such tools, they must be calibrated against reliable empirical data for a variety of situations. Detailed empirical studies could serve this purpose while providing insight into microscopic pedestrian flow characteristics under different conditions. A major gap in the knowledge is that no substantial research has examined the effects of elevated desired speeds and change in desired walking direction on collective behaviors of pedestrians. With experimental data collected under different walking conditions, this study evaluates the effects of elevated desired walking speed and change in desired walking direction on collective movements of pedestrians. Qualitative and quantitative empirical analyses suggest that larger deviations in microscopic and macroscopic characteristics can be expected at elevated desired speed levels compared with normal desired speed. Therefore, existing models that have been calibrated and validated for normal walking conditions may not be suitable for predicting collective behaviors when the desired walking speed is higher (e.g., evacuation, panic). Results obtained from these empirical studies could be beneficial for calibration and validation of the explanatory models so that those models could be applied to predict consequences under a wider range of situations.

Impacts of different angles and speeds on behavior of pedestrian crowd merging

Many forms of complex pedestrian crowd behaviors, including merging, can be identified in built environments such as public transport stations and public buildings. Understanding and capturing this phenomenon in a robust model is a challenging task; it is also a significant opportunity for research, given the international demand for models of this type. Despite the frequent occurrence of merging of crowd streams, this complex behavior has not received enough attention so far. The literature that is related to crowd merging is limited to T-shaped intersections and studies conducted on staircases. In this study using experimental data, the crowd merging phenomenon was investigated. The impacts of different merging angles and different pedestrian speeds were investigated. The results showed that flow rates and headway distributions are affected by variety in pedestrian speeds and merging angles.

Examining the Impact of Different Turning Angles on the Collective Egress of Crowds

Previous case studies of crowd disasters highlighted that collective human behaviors associated with common manoeuvres, such as turning movements, can be potentially dangerous particularly under emergency conditions. Therefore, proper consideration should be given when designing physical features such as angled or circuitous pathways at crowd-gathering places. A major gap in the knowledge is that no substantial research has examined crowding and turning-angle impacts on collective egress of crowds. In this study, to investigate the influence of turning angle on collective crowd behaviors, the authors utilize empirical data collected from human trials under normal walking conditions and from ants under panic conditions. Results obtained from analyzing empirical data from human trials suggest that higher turning angles (e.g., 60° or more) are inefficient in terms of significantly reducing the flow rates and velocities under normal/orderly evacuation conditions. This threshold angle could be reduced (e.g., up to 45°) under panic conditions, as verified with experiments with ants under panic conditions. These empirical studies are beneficial for calibration and validation purposes of the explanatory models and contribute to the development of effective evacuation strategies and design solutions for public buildings and urban environment.