**1. Introduction**

Street edges span the interface between indoor and outdoor realms along urban streets. It has been argued that they significantly impact the everyday pedestrian experience [1–3]. Understanding the nature of such experience is important against a backdrop of contemporary issues, such as high street decline [4–6] and the reduction in the variety of street edge functions [7–9]. These factors have impacted how experientially engaging and stimulating today's street edges are for pedestrians, subsequently reducing their capacity to positively influence peoples' day-to-day quality of life [10–12]. Even though this is understood, there still remains a limited systematic understanding of the general principles that characterise the way in which people visually engage with street edges [3,13,14]. This makes it challenging to guide socially and experientially responsive street edge design intervention. The current investigation addresses this lack of first-hand empirical insight through the use of mobile eye-tracking. Specifically, it assesses the extent to which pedestrians visually engage with street edge ground and upper floors, as well as street edges on di fferent sides of non-pedestrianised and pedestrianised streets. To provide greater insight, it also examines how optional and necessary pedestrian activities and di ffering streets walked influence the amount of visual engagemen<sup>t</sup> with these street edge areas. Through this study, the current investigation provides a highly detailed insight into peoples' visual engagemen<sup>t</sup> with street edges from a pedestrian perspective that has previously been challenging to capture and comprehend. The findings obtained are then used to explore how design decision-making can become more considerate of peoples' routine experiential engagemen<sup>t</sup> with street edges.

Over many years, an understanding of what visual qualities and attributes of environmental scenes people engage with and value has been attained, often with a focus towards influencing design decision-making [15–18]. Alongside this, new data collection methods have provided a greater opportunity to capture insight into how these environments are engaged with by people while they are immersed within them [19–21]. However, even though advancements have been made, the application of new techniques to the systematic assessment of how pedestrians visually engage with urban street edges remains limited. To date, existing knowledge of street edge experience has often been attained through observations and interviews [22,23]. Interviews require the verbalisation of often difficult to describe and regularly fleeting experiences [24]. Observations regularly focus upon overt human–environment interactions and are susceptible to observer bias [25]. As a result, these methods often restrict the opportunity for individual experiential influences to be systematically analysed. This is significant when reflecting upon calls for built environment design intervention to become more evidence-based through an empirical understanding of peoples' routine use and engagemen<sup>t</sup> with urban environments [26–28]. In order to overcome these methodological issues, mobile eye-tracking glasses are used during the current investigation. This data collection technique captures quantified information on gaze distribution, through tracking eye-movements, allowing a detailed understanding of specific influences on cognition and perception [29]. Recently, there have been a number of mobile eye-tracking studies in outdoor urban situations [14,21,30], as well as indoor eye-tracking studies that assess how people distribute their gaze upon images of urban settings [31–33]. This highlights a steady increase in the number of eye-tracking studies assessing how people visually engage with various urban stimuli. However, none of these studies have so far sought to use eye-tracking in real-world situations to investigate which areas of street edges people visually engage with along non-pedestrianised and pedestrianised streets. Such an assessment is undertaken during the current investigation, with the information captured providing empirical insight that develops existing understandings from a direct pedestrian perspective.

### *1.1. Visual Engagement with Street Edge Ground and Upper Floors*

It has been argued that pedestrians predominantly engage with street edge ground floors in comparison to upper floors [34,35]. For Gehl [1], ground floors are a key feature of a successful *city at eye level*. Glaser et al. [2], in an attempt to quantify ground floor experiential significance, claim that "*the ground floor may only be 10% of a building, but it determines 90% of the building's contribution to the experience of the environment"* (p. 12). From this assertion, they propose the concept of *street plinths,* with the re-appropriated use of the term *plinth* aiming to refocus attention upon ground floor social and experiential significance. Related to this is the proposition that street edges need to be understood across multiple scales [2,36,37]. Through this, there has been the opportunity to consider ground floors as being distinctly scale embedded within the wider built morphology of street edges [2,34,38]. This again highlights an attempt to focus attention upon ground floor significance, as well as to provide a greater chance for design decision-making actions to be more considerate of their specific requirements in response to peoples' engagemen<sup>t</sup> with them [2,38,39]. However, across the ideas introduced, there is a lack of empirical insight, from the first-hand experiential perspective of pedestrians, that evidences the arguments made. The current investigation will address this through a systematic assessment of pedestrian visual engagemen<sup>t</sup> with street edges using mobile eye-tracking.

Building upon the points made, little is known about the way that streets, spanning both different non-pedestrianised and pedestrianised streets, influence the extent to which visual engagemen<sup>t</sup> is predominantly focused upon street edge ground floors. Previous mobile eye-tracking research has highlighted that pedestrians visually engage with the totality of surrounding street edges to variable

extents along di fferent streets [14]. However, it is not fully understood if this insight is transferable when considering ground floors along di ffering non-pedestrianised and di ffering pedestrianised streets. Currently, there is also limited knowledge of the way in which variable pedestrian activities within streets influence ground floor visual engagement. There has recently been a growing understanding that people are situated and embodied agents experiencing their surroundings in an enactive manner that is responsive to variable social and spatial influences [40,41]. However, the extent to which specific social factors, such as varying everyday activities, influence street edge and specifically ground floor engagemen<sup>t</sup> is still not fully understood. Previous research has highlighted how contrasting activities a ffect how people behave in urban settings, providing opportunity to categorise peoples' everyday actions into optional and necessary activities [1]. Mobile eye-tracking has subsequently shown how these activity groups influence wider street edge visual engagemen<sup>t</sup> [14]. However, no studies have focused on examining the impact that these pedestrian activities have upon ground floor visual engagemen<sup>t</sup> along non-pedestrianised and pedestrianised streets. From these foundations, the current investigation asks the following:

Research Question 1a: Do people visually engage with street edge ground floors more than upper floors along (i) non-pedestrianised and (ii) pedestrianised streets? 1b: Do di fferent everyday activities and di fferent streets walked influence the amount of visual engagemen<sup>t</sup> upon street edge ground floors along (i) non-pedestrianised and (ii) pedestrianised streets?

Existing discourse provides an opportunity to hypothesise that pedestrians will visually engage more with street edge ground floors compared to upper floors along both non-pedestrianised and pedestrianised streets, [1,2,34,35]. Building upon previous eye-tracking research, that was not ground floor specific and did not systematically assess di fferences across non-pedestrianised and pedestrianised streets [14], it is anticipated that everyday activities and di ffering streets walked will influence the amount with which ground floors are visually engaged.

### *1.2. Visual Engagement with Street Edges on Di*ff*erent Sides of the Same Street*

It has been suggested that pedestrians engage with street edges on opposing sides of a street di fferently [1,34,37]. Along non-pedestrianised streets, the street edge on the walked side is experienced at a closer, more-detailed range and as a result, is able to capture and hold pedestrian engagemen<sup>t</sup> to a greater extent. The opposite street edge cannot be engaged as closely and objects in the street often hinder prolonged engagement. Even though this is understood, there is limited empirical evidence from a pedestrian perspective highlighting the disparity in engagemen<sup>t</sup> between the walked and opposite side street edges of the same non-pedestrianised street. Street edges along pedestrianised streets cannot be delineated as walked and opposite, with pedestrians often able to occupy much more of the street space between the edges [42,43]. These street edges are instead left and right sided from a pedestrian perspective. Significantly, we currently lack empirical knowledge of the way in which these street edges of the same pedestrianised streets are visually engaged with. Similar to understandings of ground floor visual engagement, it is currently not known how visual engagemen<sup>t</sup> with street edges on di fferent sides of non-pedestrianised and pedestrianised streets varies in response to everyday pedestrian activities and di fferent streets walked. The current investigation will use mobile eye-tracking to address the lack of knowledge in this area, while asking the following:

Research Question 2a: Are there di fferences in the amount of visual engagemen<sup>t</sup> upon street edges on di fferent sides of the street along (i) non-pedestrianised and (ii) pedestrianised streets? 2b: Do di fferent everyday activities and streets walked influence the amount of visual engagemen<sup>t</sup> upon street edges on di fferent sides of the street along (i) non-pedestrianised and (ii) pedestrianised streets?

It is predicted that visual engagemen<sup>t</sup> will be focused towards the street edge on the walked side of non-pedestrianised streets [1,34,37]. In contrast, visual engagemen<sup>t</sup> with street edges of pedestrianised streets will be more balanced across both sides. Building upon the understanding that di ffering activities and streets walked impact street edge visual engagemen<sup>t</sup> overall [14], it is predicted that such factors will also influence the amount that street edges on the walked and opposite sides of non-pedestrianised streets, as well as edges on the left and right sides of pedestrianised streets, are visually engaged with.

### *1.3. The Influence of Pedestrianisation upon Visual Engagement with Urban Street Edge Areas*

The broad benefits of pedestrianisation have been detailed by many [1,35,42,43]. However, it is not understood how such intervention impacts pedestrian engagemen<sup>t</sup> with street edges. Specifically, there has been no systematic exploration of how visual engagemen<sup>t</sup> with areas of street edges along pedestrianised streets contrasts with that of street edges areas of non-pedestrianised streets. Therefore, the current investigation asks the following:

Research Question 3: Are there di fferences in the amount of visual engagemen<sup>t</sup> upon (i) street edge ground floors between non-pedestrianised and pedestrianised streets, and (ii) street edge sides between non-pedestrianised and pedestrianised streets?

The experiential significance of street edge ground floors has been described, often regardless of context [1,2,34]. It is therefore hypothesised that there will be no significant di fference in the amount of visual engagemen<sup>t</sup> with ground floors between non-pedestrianised and pedestrianised streets. It is anticipated that visual engagemen<sup>t</sup> will be more balanced across both street edges of pedestrianised streets, in contrast to non-pedestrianised streets, where it will be focused on the edge on the walked side [1,34,37]. This provides the opportunity to hypothesise that there will be a noticeable di fference in the amount of visual engagemen<sup>t</sup> upon the di fferent street edge sides between non-pedestrianised and pedestrianised streets.
