# Real-Time Monitoring of Passenger's Psychological Stress
## 1 Introduction  
### General Background and Motivations  
Stress is an umbrella term for some psychological, physiological and behavioral response to environmental factors we perceive as a potential threat. In the short run, it should boost our ability to cope with this kind of stimuli: stress hormones are released in the body and the sympathetic nervous system has increased activity [1], bringing the entire organism in a general state of alarm. When the threatening stimulus is repeated or lasts over too much time, _acute_ stress (the natural emotional response) becomes _chronic_, and may turn into mental disorders. From a psychological viewpoint, the recurrence of too many daily hassles is a threat to an individual's wellbeing [2]. From a clinical viewpoint, it may have heavy impacts on health [1]. Stressful events (or surroundings) are frequently encountered during daily urban trips. In the middle 1980s, an extensive survey based on people's answers to a detailed questionnaire tried to quantify the phenomenon [3]. Participants included 1167 Italian workers, and 437 Dutch people whoworked in the production unit of a heavy engineering company. Part of these people went through long commuting distances from home to the working place. Regarding the Italian people, experimenters found significantly higher scores in chronic psychological stress for the commuting people than for non-commuters. Those people also demonstrated more complaints, illnesses and absenteeism due to sickness. Similarly, the Dutch commuters showed a significant increase in stress disorders (tiredness, edginess, irritability, lack of concentration and difficulty in sleeping) compared to the non-commuting Dutch people. This increase was only a trend for non-production workers, suggesting that stress disorders due to everyday travels are widespread but worsen with poorer living standards. In a broader context, it has been shown that different travelling options have distinct effects on passengers' stress and mood [4]. For example, perceived crowding appears a major cause of discomfort among train passengers, and therefore increases their psychological stress [5]. Stress and mood during a journey are also mediated by a host of factors, like comfort and effort, with respect to the individual, or control and predictability, regarding their environment [5; 6]. This relationship is very similar to the one found in the working medium: that is why stress experienced by frequent travellers have sometimes been compared to actual job strain [3]. An objective feedback on passengers' mental states would enable smart environments to adapt and increase people's ability to cope with every hassle of a daily trip--and thus help prevent chronic stress onset. Since acute stress has short-term physiological correlates (e.g., sympathetic activation), various peripheral signals (such as heart rate) may be used to monitor human stress levels, in real-life settings, by means of the numerous wearable sensors that recently popped in the public market [7]. Regarding smart environments, the H2020 BONVOYAGE project aims to design a digital platform optimizing the multimodal door-to-door transport of passengers and goods. The platform integrates travel information, planning and ticketing services, by automatically analyzing offline data from heterogeneous databases (on road, railway and urban transport systems), as well as real-time measured data (traffic, weather forecasts), user profiles, and user feedbacks. Among those feedbacks, passenger's stress levels are assessed from physiological signals recorded by wearable sensors during the travels are used for user profiling. This allows for the tailoring of transport solutions, which are proposed to the user in order to improve their travelling experience--notably, to diminish their levels of transport-related psychological stress. This paper aims at introducing a pilot study conducted in that framework: psychological stress was estimated from physiological signals recorded on the same participant during two half-day journeys.