# Behavioral Dynamics of Pedestrians Crossing between Two Moving Vehicles
## 2 Methods  
### Data Collection  
Sixteen children (of age 12.2 \(\pm\) 0.8 yrs, i.e., mean age 12.2 years and standard deviation 0.8 years), sixteen young adults (of age 22.8 \(\pm\) 2.6 yrs), and fourteen elderly people (of age 54.1 \(\pm\) 4.9 yrs) with normal or corrected-to-normal vision were recruited for this experiment. Informed written consent was obtained from all individual participants. The experiment was conducted in accordance with the Declaration of Helsinki, and the protocol was approved by the Kunsan National University Research Board. Each subject was placed on a customized treadmill (of dimensions 0.67 m wide, 1.26 m long, and 1.10 m high) with four magnetic counters that track movements. A Velcro belt connected to the treadmill is worn to decrease vertical and lateral movements, and a handrail is placed for stability. The treadmill turns with minimal friction as the participants walk, and magnetic counters track rotations (left panel, Figure 1). Each participant wore an Oculus Rift (Menlo Park, CA, USA) DK1 virtual reality headset connected to a standard desktop PC. The headset portrayed a realistic view of a street with a crosswalk in 1280 \(\times\) 800 resolution 3D stereoscopic visual images that respond realistically according to the participant's movements. Practice trials were performed prior to the experiments to familiarize each participant with the treadmill and virtual environment before the experiment. (see [4] for details).  
A diagram of the virtual crossing situation is given in Figure 2. The participant, standing at rest before a car lane with a \"ready\" signal shown, was instructed to press a button when a \"go\" signal appears, and then to look at her/his left side, from which two vehicles, one in front of the other, were moving at equal constant speed \(v_{c}\). The participant was instructed to cross between the two vehicles if she/he believed she/he could cross successfully. If a collision with a vehicle occurred, the simulations halted. The experimenter recorded whether there was a successful crossing, a collision, or no crossing.  
The experiment was designed to examine the participants' responses to a single gap, and so only two vehicles were present. We examine the responses of the participants to changing gap characteristics by varying experimental parameters. These include pedestrian starting position \(y_{0}\), gap time \(t_{g}\) (or gap length \(l_{g}\)), vehicle speed \(v_{c}\), and the vehicle type (sedan or bus). Details of age groups and a full list of experimental parameters are given in Table 1.  
The gap center is defined to be the midpoint of the gap between the vehicles. While the width of the gap and speed of the vehicles are varied, the initial position \(x_{0}\) of the gap center is always set in such a way that the gap center reaches the interception point at time \(t=4\) s. Accordingly, we have \(x_{0}=-v_{c}\times 4\) s.  
Figure 1: Images of experimental setup. Left panel: photograph of student participating in an experiment. Middle panel: cartoon crosswalk used for calibration. Right panel: Screenshot of the virtual crosswalk used in the experiment.  
Figure 2: Top-down diagram of the crossing environment at time \(t=0\). The two boxes on the road depict two vehicles facing the right, which move forward at a constant speed. The circle depicts the pedestrian, who begins at rest and is facing in the direction the arrow. Labeled are experimental parameters \(l_{g}\), \(y_{0}\), and the bearing angle to the crossing point \(\theta_{c}\).