2  Literature Review

Keywords

travel behavior, mental health, motivation, suicidality, activity types, DBSCAN-TE

Mental health and well-being are complex issues influenced by a multitude of factors, including social and environmental elements. Addressing these factors is essential for promoting individual well-being (Barry, 2009). Additionally, travel behavior has been recognized as a significant factor impacting social and mental health (Delbosc & Currie, 2011). In this review, we explore current research on the impacts of built and natural environments, social isolation, travel behavior, and activity types on mental health and well-being. We also examine the well-being and travel behavior of individuals with autism and social anxiety. Ultimately, we integrate these factors to highlight how our research aims to fill an existing gap related to the literature.

2.1 Impacts of Built and Natural Environments

Part of the increase in mental health problems come from factors that limit people’s engagement with the world around them since positive mental health coincides with people’s ability to access the natural environment. Recent researchers have underscored the therapeutic benefits on mental health of engaging with green and blue spaces, ranging from parks and forests to oceans and rivers, in alleviating stress and anxiety, enhancing mood, and bolstering cognitive function (Pouso et al., 2021; White et al., 2021). Green and blue spaces help support good mental health, but these spaces, the very thing that can help with mental health issues, are often inaccessible. Urbanization, for example, magnifies the predicament by reducing access to these spaces, thereby impeding efforts to foster mental well-being. In addition, the implementation of lockdowns and social distancing measures during COVID-19 further exacerbated this issue by limiting many individuals’ interactions with nature, which was one observed major shift in travel patterns (Pouso et al., 2021).

In addition to facilitating access and engagement with the world, the built or urban environment significantly impacts well-being. Researchers in Brussels, Belgium, found that noise pollution, air pollution, and lack of green space were linked to higher levels of depressive symptoms and stress, whereas proximity to green spaces was associated with lower levels of stress and depressive symptoms (Pelgrims et al., 2021). A systematic review of the literature by Rautio et al. (2018) confirmed these findings, underscoring the relationship between the living environment and depressive mood. Overall, access to natural spaces within urban areas is crucial for mental well-being. Urban planning should prioritize green and blue spaces to mitigate stress and depressive symptoms associated with urbanization. Balancing development with the preservation of these natural spaces is essential for promoting public mental health.

2.2 Impacts of Social Isolation

Social isolation, or social exclusion, affects individuals’ mental health. When looking specifically at the effects of the COVID-19 pandemic, Loades et al. (2020) focused on the impact of social isolation and loneliness on the mental health of children and adolescents. The authors conducted a rapid systematic review of existing literature on the topic and found that social isolation and loneliness can have a negative impact on mental health, including increased symptoms of anxiety, depression, and post-traumatic stress disorder. Barry (2009) reviewed the determinants of positive mental health, emphasizing the importance of social support and social connectedness, a sense of control and autonomy, self-esteem, and meaning and purpose in life. She argues that mental health promotion should focus on building resilience, enhancing positive emotions, and developing skills and competencies to manage adversity. Many of these competencies are related to social interactions and avoiding social isolation (Barry, 2009).

While significant periods of isolation, like during the COVID-19 lockdowns, reduced social interactions, everyday sociality is influenced by one’s ability to travel. Researchers in Melbourne, Australia, studied the link between mobility, social exclusion, and well-being. They found that increased mobility improved well-being and reduced social exclusion, positively impacting mental health (Stanley et al., 2011). Another study in Melbourne, Australia, explored how transport disadvantage and social exclusion affect well-being. Using survey data, researchers found that both factors negatively impact well-being, with social exclusion having a stronger effect (Delbosc & Currie, 2011). The ability and choice to make trips affects well-being and mental health of individuals.

Overall, these results suggest that social exclusion and isolation, transport disadvantage, and loneliness can negatively impact individual well-being and mental health. On the other hand, mobility and contact with others can have a positive impact on individual well-being. These findings highlight the importance of social support networks and access to transportation to facilitate social interactions.

2.3 Impacts of Travel Behavior

Research on travel patterns highlights the relationship between travel behavior and individuals’ social and mental well-being. Syahputri et al. (2022) conducted a study in the Bandung Metropolitan area to investigate the effect of travel satisfaction, linked to mental health, and activity travel patterns of household members. This study showed that travel satisfaction is positively correlated with social health and mental health. Individuals who spent more time working or studying at home had higher travel satisfaction, leading to better social and mental health. However, extended time on obligatory activities limited interactions with household members, which negatively affected mental health. Encouraging travel for those with significant commitments can enhance travel satisfaction, social health, and mental health. Additionally, regular daily activity travel patterns with breaks from obligations were linked to improved mental health.

Similarly, another study investigated how travel affects emotional well-being and life satisfaction. The researchers pointed out that those who regularly traveled to work experienced less life satisfaction than those who worked from home. However, the study revealed a positive association between general travel and emotional well-being, indicating that travel experiences contribute to improved mood and life satisfaction. Overall, these findings underscore the importance of integrating travel into daily routines to foster better mental health and overall well-being (Friman et al., 2017).

The reviewed studies highlight the significant influence of travel behavior on social and mental health outcomes. Factors such as travel satisfaction and activity travel patterns of household members play crucial roles in shaping these outcomes. Additionally, positive travel experiences are associated with improved emotional well-being and life satisfaction.

2.4 Impacts of Activity Types

People engage in various types of activities which can impact mental health and overall well-being. For instance, Takiguchi et al. (2022) found that the types of activities people engage in can significantly affect the extent of positive emotions experienced. By analyzing various activity settings like green spaces, grocery stores, libraries, and social recreation spaces, we aim to uncover the potential benefits and implications of these activity locations on mental health and overall well-being.

2.4.1 Green Spaces

The role of green spaces in enhancing mental well-being has increasingly captured attention, with numerous studies attesting to their beneficial effects across diverse demographics and environments. This section explores the impact of spending time in green spaces on mental health.

Primarily, exposure to nature is consistently correlated with reduced stress, anxiety, and depression levels. For instance, participants who embarked on a 90-minute walk in natural settings exhibited decreased activity in the subgenual prefrontal cortex—a region linked to rumination and heightened mental health risks—compared to urban walkers (Bratman et al., 2015). Similarly, a meta-analysis of 25 studies indicated that natural environments positively influenced overall mental well-being, indicated predominantly through participants’ self-reported emotional states (Bowler et al., 2010).

Long-term exposure to green spaces also yielded positive mental health outcomes. Research by Gascon et al. (2018) revealed lower anxiety and depression levels in adults residing near green and blue spaces. Similarly, participants perceiving significant greenery in their neighborhoods exhibited notably better physical and mental health outcomes (Sugiyama et al., 2008). Furthermore, another study found that living in areas with increased green space concentration was correlated with lower salivary cortisol levels, indicative of reduced stress (Roe et al., 2013). Time spent in green spaces is associated with reduced levels of stress, anxiety, and depression.

While the relationship between green spaces and mental health is intricate, recent studies uniformly advocate for their positive influence. In sum, exposure to green spaces alleviates stress, anxiety, and depression, rendering them a promising avenue for enhancing mental health and overall well-being.

2.4.2 Grocery Stores

Supermarkets and grocery stores are integral to modern life, serving as essential hubs for purchasing food and household necessities. However, the experience of shopping in these environments can influence individuals’ mental well-being. This section aims to investigate the effects of time spent in grocery stores on mental health.

A study surveyed 239 volunteers across 29 focus groups, exploring stress in the context of grocery shopping. Participants expressed stress related to time pressure, crowd density, employee attitudes, and store layout, as well as environmental factors such as music and lighting, and product availability (Aylott & Mitchell, 1998). No quantitative data were gathered and stress was not measured before or after spending time grocery shopping - these were just stresses that participants expressed experiencing while grocery shopping. While this study is from 1998, it sheds light on the stress experienced in the context of grocery shopping and shows that stress while grocery shopping is not a new issue.

As previously mentioned, time pressure experienced at grocery stores can induce stress. In one study, 1,023 participants responded to a questionnaire about grocery shopping and shopping satisfaction, specifically addressing how shopping satisfaction related to time pressure. Researchers found that time pressure had varying effects on satisfaction depending on whether it was a major shopping trip or a quick shopping trip for a few items. They found that overall, women were less satisfied with their shopping experience when under time pressure and men were satisfied with their shopping experience when under time pressure. Overall, time pressure had a negative impact on shopping satisfaction, although other factors also influenced customer experiences (Nilsson et al., 2017).

2.4.3 Libraries

Libraries serve as indispensable community resources, providing access to information, educational materials, and spaces for learning and social interaction. Beyond their traditional roles, libraries have increasingly been acknowledged for their potential to positively impact mental health and well-being. This section seeks to explore the diverse ways in which libraries can influence mental health outcomes.

Existing literature strongly supports the notion that libraries promote positive mental health and well-being. One literature review highlighted the mental health support offered by many libraries, noting the comforting atmosphere provided to patrons, often attributed to the supportive library staff (Elia, 2019). Similarly, another study described public libraries as offering a therapeutic landscape that is welcoming, comforting, calming, empowering, and overall conducive to well-being (Brewster, 2014).

Moreover, libraries often offer specialized programs and services aimed at promoting mental health and well-being. For instance, they may host mental health workshops, employ social workers, or introduce therapy dog programs to provide emotional support and coping strategies for patrons facing mental health challenges (Elia, 2019). Some libraries even have employees trained in bibliotherapy, a therapeutic approach that uses books and literature to support mental health outcomes. A systematic literature review synthesized evidence on bibliotherapy services at public libraries, revealing its effectiveness in aiding individuals with anxiety, stress, depression, and other issues (Zanal Abidin et al., 2023). This coupling of access to literature with trained bibliotherapy professionals enhances mental health outcomes for library patrons.

In sum, libraries play a multifaceted role in promoting mental health and well-being through resource accessibility, community engagement, and supportive environments. Their positive impact on individuals’ mental health outcomes is evident in the literature.

2.4.4 Social Recreation

Social recreation spaces, such as restaurants, theaters, malls, and leisure spots, play a significant role in providing opportunities for socialization, relaxation, and entertainment. Despite their ubiquity, the impact of time spent in these environments on mental health is complex. This section explores the effects of social recreation spaces on mental health outcomes, drawing insights from recent research.

Leisure activities, which individuals choose to engage in when free from obligations, enhance well-being by eliciting positive emotions and fostering long-term stress-coping mechanisms (Takiguchi et al., 2022). Longitudinal studies support the positive link between leisure satisfaction and well-being over time (Kuykendall et al., 2015). However, the quality of social interactions within these spaces can significantly affect individuals’ well-being. A study found that negative interactions were linked to lower quality of life, while supportive interactions corresponded with higher quality of life(Yanos et al., 2001). This highlights the importance of social interaction dynamics in shaping well-being.

Furthermore, limited research exists on the impact of social deprivation or isolation on adolescents and adults. Self-reported loneliness is linked to mental health issues, but disentangling the causal relationship between loneliness and mental well-being remains challenging. It is often unclear whether loneliness causes poor mental health or vice versa. Experimental studies on human loneliness face hurdles, as loneliness is not solely due to social deprivation as some individuals feel lonely even in crowded environments (Orben et al., 2020).

Social recreation spaces have a multifaceted influence on mental health outcomes, offering platforms for social interaction and stress alleviation while harboring potential risk factors contingent upon the nature of these interactions. The intricate interplay between activities in these environments and mental well-being suggests that visits to social recreation locations may either bolster or diminish overall well-being, contingent upon the nature of social interactions experienced therein.

2.5 Neurological and Psychological Typology

Navigating the intersection between mental health and travel behavior unveils a complex relationship that significantly influences individuals’ daily lives. In this section, we look at the relationship between specific neurological and psychological conditions—autism spectrum disorder (ASD) and social anxiety—and their corresponding impacts on travel behaviors and overall well-being. Through recent research, we explore how autistic individuals and individuals with social anxiety navigate transportation challenges, revealing unique patterns that shape their mobility and mental health outcomes.

2.5.1 Autism

ASD, commonly referred to as autism, presents as a lifelong neurodevelopmental condition characterized by challenges in social communication and social interaction. In addition, autistic individuals tend to engage in restricted and repetitive behaviors. We use the term, “autistic”, as recommended by many self-advocates we know who prefer the identify-first label “autistic” over person-first terminology “individual with autism spectrum disorder (or condition)” (Kenny et al., 2016). Although typically diagnosed in early childhood, many autistic individuals may remain undiagnosed until later in life (Ridgway et al., 2024). Research comparing the well-being of autistic and non-autistic individuals highlighted significant disparities, with autistic individuals often exhibiting lower levels of well-being, particularly evident among college students who grapple with challenges in social connectivity and balancing academic demands (Bailey et al., 2020; Ridgway et al., 2024).

Despite its prevalence in many fields, autism remains relatively underexplored in transportation literature, with existing transportation surveys failing to neurologically categorize individuals. Recent studies have begun to address this gap, shedding light on the travel behaviors and experiences of autistic individuals. Surveys conducted among autistic adults in New Jersey underscored their reliance on others for transportation, often resulting in missed opportunities due to the unavailability of rides. Moreover, firsthand accounts from autistic individuals and their caregivers highlight feelings of isolation and depression stemming from transportation-related struggles (Deka et al., 2016; Lubin & Feeley, 2016).

These findings collectively suggest a potential link between lower well-being and less activity engagement illustrated by travel behaviors among autistic individuals, emphasizing the need for tailored support and inclusive transportation systems.

2.5.2 Social Anxiety

Social anxiety involves an overwhelming fear of embarrassment or rejection from others and refers to the anxiety stemming from anticipated or real interpersonal judgement in social situations. These fears and anxieties tend to lead socially anxious people to be more socially isolated than others (Leichsenring & Leweke, 2017; Öztürk & Mutlu, 2010; Ye et al., 2021). Frequently mistaken for shyness, social anxiety remains underrecognized, with a lifetime prevalence of 13% and a 12-month prevalence of 8% among adults and adolescents in the United States (Leichsenring & Leweke, 2017).

Two studies examining the relationship between social anxiety and well-being found a negative correlation between the two variables. These studies looked at social anxiety experienced by participants, and not necessarily at participants who have social anxiety disorder, which is a persistent state of social anxiety that can cause major impacts or changes in one’s daily life (Leichsenring & Leweke, 2017). In one study, Öztürk & Mutlu (2010) investigated the correlation between social anxiety and well-being among university students. They observed that higher levels of social anxiety were associated with lower overall well-being. Similarly, Ye et al. (2021) found a significant negative correlation between social anxiety and well-being among Chinese college students.

When considering the impact of anxiety disorders on travel patterns, Ratering et al. (2024) studied the travel behavior of 40 Dutch adults diagnosed with anxiety disorders. They noted that individuals with anxiety disorders, including social anxiety, often faced mobility limitations due to anxiety-related concerns. Participants in the study used coping mechanisms such as traveling with familiar companions, avoiding certain locations, or staying at home altogether (Ratering et al., 2024).

Overall, heightened social anxiety is associated with reduced well-being and may prompt individuals to modify their travel behaviors, potentially resulting in fewer trips and less activity engagement.

2.6 Current State of the Research

Recently, a research group used mobile phone-based sensing to study daily activities and environmental exposures in relation to anxiety symptoms. Lan et al. (2022) explored how individuals’ activities in different environmental settings contributed to anxiety levels, using cross-sectional data from mobile phone sensors like global position services (GPS) and accelerometers to track spatial movements and activity patterns. Anxiety symptoms were measured with a standardized questionnaire, and environmental exposures such as air pollution, noise, and green space availability were assessed.

The study found that time spent in areas with higher air pollution and noise was associated with increased anxiety, while time in green spaces was linked to lower anxiety symptoms. Physical activity and social interactions in various environments also correlated with reduced anxiety. This study began to explore how individuals’ travel can affect anxiety symptoms, but this study had limitations. GPS data were collected over a seven-day period, with anxiety levels assessed using a single questionnaire asking participants to reflect on the past two weeks. The study tracked exposure to various areas but did not pinpoint where specific activities occurred. Additionally, participants were not categorized into specific groups based on neurological or psychological conditions.

To address these gaps, this thesis takes a longitudinal approach, collecting location-based services (LBS) data from participants over one month to a year. Participants completed mental health surveys up to twice daily, allowing for more detailed and frequent assessments of mental health in relation to daily travel habits. Unlike the previous study, we identifed and analyzed specific activities rather than just GPS trajectories, ensuring accurate identification of where activities occurred. Furthermore, participants were categorized into groups—autism, social anxiety, and control—based on psychological evaluations. This approach enables a deeper analysis of travel behavior and mental health across different population segments, providing insights that can inform more targeted interventions.

2.7 Summary

Overall, this literature review examines various factors impacting mental health and well-being, focusing on the built and natural environments, social isolation, travel behavior, activity types, and the unique challenges faced by autistic individuals or those with social anxiety.

Access to green and blue spaces is crucial for mental health, as they help reduce stress and improve mood. However, urbanization and COVID-19 restrictions have limited access, worsening mental health issues. High pollution and lack of green spaces in urban areas are linked to increased stress and depression. Social isolation, exacerbated by the pandemic, has heightened anxiety and depression. Mobility and social support are key to mitigating these effects, making transportation access and social interactions essential. Positive travel experiences and regular travel are associated with better mental health. Green spaces significantly reduce stress, while grocery shopping can be stressful. Libraries and social recreation areas support well-being, whereas individuals with autism and social anxiety face unique travel challenges, leading to isolation and limited mobility.

Recent studies using mobile phone-based sensing have explored the relationship between environmental exposures, activities, and anxiety. This thesis addresses gaps by using longitudinal data to assess mental health impacts of travel behavior across three groups of individuals, aiming to understand the link between travel behavior and mental health.