## 2 Existing Studies on the Platform-Train Interface
The authors found that passengers presented difficulties boarding and alighting when there are different steps at the train doors. Some authors [8; 28] studied the effect of platform-edge doors on the behavior of passengers, in which accessibility is related to the formation of lines of flow, the distance between passengers, and the speed passengers and space used by each passenger. To implement platform-edge doors, level access is needed between the platform and the vehicle. These elements work as barriers to prevent passengers from falling onto the tracks, reducing the number of suicide acts and accidents, due to the doors being closed until the vehicle arrives and before it leaves. Passengers in waiting areas such as the platform-train interface behave differently from those who are in the circulation zone. For [PERSON] and [PERSON] [29] there are two main types of behavior of passengers who are waiting: queuing or clustering to the side or in front of the doors. Other authors such as [PERSON] [30] considered the whole platform as a waiting area to study the distribution of passengers waiting to board. The author states that the distribution of passengers on the platform depends on various factors: the position of the platform exit at their destination station, the search for the least crowded carriage, how crowded the platform is (e.g., if there is no space to move along the platform passenger will wait near the entrance of the platform), and whether there are markings of the position of doors on the platform. There are also some passengers who are located because of random variables (e.g., meeting with a friend). To reduce the interaction between passengers waiting to board the train, [PERSON] and [PERSON] [31] recommended using a rectangular area or \"keep out zone\" marked on the platform. In this case, boarding passengers were located outside this rectangular area, preventing them from being an obstacle to those who are alighting. [PERSON] et al. [32] studied the distribution of passengers, in which design and technology could motivate passengers not to congregate in front of a particular door when boarding the train. [PERSON] et al. [33] studied the effect of waiting areas on the behavior of passengers boarding and alighting. [PERSON] et al. [34] reported that the vertical or horizontal gap should be less than 5 cm, especially when considering passengers with reduced mobility. [PERSON] and [PERSON] [35] studied the space used by a wheelchair-user considering different levels of demand when waiting to board the train. Recently, through laboratory experiments, [PERSON] et al. [36] studied a vertical handrail for wheelchair users to improve accessibility when boarding and alighting the train. With respect to signs in metro stations, [PERSON] et al. [37] studied the color of signs in a fire escape. The authorsused eye-tracking and physiological data as indicators during the experiments. Moreover, [PERSON] and [PERSON] [38] studied the distribution of passengers on the platform by means of real-scale experiments, in which the distance between the platform-edge doors and the yellow safety line was a determinant for the interaction between passengers. Despite the important research done, new experiments are needed to better represent the behavior of various types of passengers and study their accessibility in different spaces. In particular, there is a need to carry out new studies to identify the effect of accessibility elements such as the yellow line on passenger behavior at the platform-train interface, which was the main objective of this paper.