Urban design and public transportation – public spaces, visual proximity and Transit-Oriented Development (TOD)

ABSTRACT

Walking distances conventionally define service areas for public transportation and urban growth boundaries for Transit-Oriented Development (TOD). Urban designers accordingly draw rings around transit stops and arrange transit-supportive land uses within 10-minute walksheds. This approach to TOD neglects processes of creating public spaces in visual proximity of transit stops. This paper proposes a methodology to analyze public spaces and looks at how commercialization and public space patterns unfold through viewsheds around transit stops. The results reveal amoebic TOD patterns of public spaces that are much smaller than conventional walking radii. This alternative viewshed approach can be helpful in designing TODs.

Introduction

Unsustainable mobility is a major challenge in cities. Urban designers can help in mitigating environmental problems caused by increased automobile travel and urban sprawl by creating urban forms that encourage walking and increase the use of public transportation. Transit-Oriented Development (TOD) is a planning policy of designing and developing walkable, dense and diverse neighbourhoods and concentrating urban growth around transit stops to support higher usage of public transportation. The policy creates a virtuous cycle of environmental responsible mobility where compact developments around transit stops inspire a modal shift from cars to walking and transit and vice versa (Calthorpe 1993; Cervero & Sullivan, 2011; Bertolini, Curtis, and Renne 2012).

TOD is usually defined by comfortable walking distances to a designated transit stop (notably by Calthorpe 1993). Transit professionals have established heuristics of 5 to 10-minute walking distances to transit stops. This is usually a radius of 300–400 m (about a quarter mile) or 600–800 m (a half mile) around bus stops and rail stations. Urban designers and planners draw rings around transit stops according to these rules and arrange transit-supportive land uses (such as a horizontal and vertical mix of dense residential, retail, commercial and public uses) within the circular walksheds. Many researchers have studied user willingness to walk further to and from a transit stop (Mulley et al. 2018) and the possibility to ‘burst the half mile bubble’ (Canepa 2007) and extend the radii of TOD (Guerra, Cervero and Tischler 2012). However, there is no research on public spaces that focus building orientation and neighbourhood activity within the TODs (as discussed in the TOD principles of Calthorpe 1993).

The approach on TOD in this paper emphasizes patterns of public spaces in visual proximity to transit stops. Visual proximity is defined by viewsheds from transit stops. The viewshed is an urban space with clear visual acuity of approximately 100 m. Pedestrian activity triggers commercialization within the viewsheds of transit stops and creates a pattern of public spaces. Commercialization can extend over the viewshed of the transit stop following the dispersal patterns of passengers. Calthorpe (1993) refers to these commercialization and public space patterns around transit stops as commercial core areas of TODs. He intuitively draws larger or smaller commercial cores in different types of TODs, but does not discuss specific urban design elements and how they influence the creation and expansion of the commercial core.

TOD is conventionally understood as a neighbourhood development pattern defined by a circular walkshed and implies an urban design practice informed by two-dimensional zoning. This is problematic because the integration of public spaces with transit stops is three-dimensional. Architects and urban designers have proposed design guidelines and Form-Based Codes (FBCs) as a way to go beyond conventional zoning regulations by proposing codes and typologies of urban design elements (Duany and Talen 2002; Walters 2007; Talen 2009, 2013). To improve the design guidelines and FBCs for TOD, there is a need to identify urban design elements and understand how they influence processes of public space creation around transit stops. Transit stops, street spaces, commercial storefronts and other facades are urban design elements that are critical to TOD. The design guidelines and FBCs usually include typologies of design elements. The type of transit stop plays a crucial role in integration with the city.

This research asks the following question: what type of commercialization and public space patterns unfold around typical transit stops and how do they relate to viewsheds and walksheds? The research hypothesis is that transit stops, classified by their segregation from the street, are an underlying element of urban form. They create particular elongated and amoebic patterns that are markedly different from circular walksheds. Four types of public transportation systems and transit stops can be classified by their level of segregation: (1) transit stops on streets; (2) train and bus stations of completely segregated transit systems (on the ground or elevated); (3) subway stations; and (4) bus or tram stops on partially segregated busways or railways on the ground (Stojanovski 2013). Each type of transit stop connects to the street space in a unique way and produces specific development patterns with the surrounding buildings. Transit stops on the streets integrate with cities without any barrier effect. The loading platforms are on the sidewalks and the street works as one urban space. Segregated train and bus stations have exits and need a complex network of corridors, stairs and escalators to reach the loading platform. Partially segregated transit stops are also part of street spaces, but it is not always possible or safe to cross the street. This gives a unique context of permeable and impermeable barriers along the street because of additional urban design elements such as greenery, fences, and so on (Figure 1).

Figure 1. Typology of public transportation systems

This paper proposes a methodology to analyze public spaces and investigates how commercialization and public space patterns unfold in viewsheds around transit stops in three Swedish cities. The first section presents the research question and hypothesis about shapes of TOD patterns of public spaces around transit stops. TOD patterns of public spaces are urban spaces enclosed by commercial storefronts and public buildings (libraries, theatres, healthcare facilities, post offices, places of worship and assembly, and so on). The second section develops a theoretical background to analyze public spaces based on urban morphology and visual perception. Urban form can be understood as a composition of urban design elements (Conzen 1960; Alexander, Ishikawa, and Silverstein 1977; Alexander 1979; Taylor 1999; Marshall 2016). The particular arrangement of urban design elements that are visually perceived can support or hinder mobilities. Walking depends on the design of streets, sidewalks, buildings, commercial activity in buildings, and so on (Ewing et al. 2005; Mehta 2008; Ewing and Handy 2009). To achieve effective integration with public transportation systems, urban designers must focus on the interplay of urban design elements such as the type of transit stop, the street and aligning the facades of surrounding buildings, and so on. The Methodology section describes the procedure of surveying and mapping public spaces in visual proximity to transit stops based on the public or private character of the street and buildings adjacent to the transit stops. This follows on Jacobs (1961) who emphasizes the importance of the interaction of the street and buildings as two urban design elements. The Findings section presents maps of TOD patterns of public spaces in three Swedish cities. These amoebic and circular shapes are arguably the most effective in terms of increasing passenger trips and, as such, are more important than walksheds. Empirical research on walking distances shows that passengers walk up to 2000 m to reach a transit stop (El-Geneidy et al., 2014). The number of generated passengers within 100–200 m is almost double than within 300–400 m for bus and tram stops on streets (O’Sullivan and Morrall 1996; Daniels and Mulley 2013). The final two sections discuss the results and conclude with implications for urban design and recommendations for further research.

Theoretical background

To develop a methodology for analyzing public spaces patterns, the theoretical background builds upon research from urban morphology and visual perception in urban space (Cullen 1961; Hall 1966; Gibson 1986; Gehl 1987). Studies that focus on street spaces, street and building façade interaction or visual assessment (Appleyard 1981; Ewing et al. 2005; Ewing and Handy 2009; Mehta 2009; Lee and Talen 2014) are also relevant literature. Urban morphology is relevant due to its focus on urban elements and patterns (Moudon 1997), as well as the transformative physical processes of incremental growth and the formation of centres (see Alexander, Ishikawa, and Silverstein 1977, 1987; Alexander 1979; Scheer 2010) and commercialization of urban forms (see Davis 2009; Narvaez, Penn, and Griffiths 2015). The following two subsections describe theories about the visual experience of urban space and commercialization. The commercialization of the buildings surrounding transit stops is crucial because it creates public spaces and attracts pedestrians as potential transit patrons.

Visual experience of urban space

Visual experience between a building and a transit stop involves a sequence of viewsheds (Cullen 1961, 1967). The viewshed is an urban space with clear visual acuity. The viewshed combines elements of the visual world and the visual field (defined by Gibson 1986). The visual world is like a sphere around a person and is clear everywhere while the visual field is the area within the field of view of both eyes. The field of view is clear in the centre (foveal vision) and vague in the periphery (Figure 2a). The viewshed is a circle (planar projection of the visual world) in the foveal plane within a radius of 100–200 m. The viewer identifies affordances (Gibson 1986). This includes transit stops, entrances to buildings and shops, storefronts, people to communicate with, and so on.

Figure 2. Visual perception of urban space

Jan Gehl (1987) differentiates between different tactile, speaking, hearing and visual ranges (Figure 2b). He refers to the visual range of 70–100 m as the social field of vision. Within this distance, human figures become individuals and it is possible to notice the person’s sex, approximate age and activity. Architects design football fields and stadiums in this visual range so that spectators can see the activities on the field. This distance also corresponds to the size of a traditional city block and the smallest neighbourhood size as defined by close neighbourly interactions (Lee 1968; Canter 1977; Appleyard 1981; Ceccato and Snickars 2000; Talen and Shah 2007). Visual proximity to transit stops refers to urban elements (buildings, building façades, streets, sidewalks, commercial storefronts, and so on) in the viewshed. Empirical evidence shows that the generation of passengers is at its maximum within 100–200 m walking distance from a transit stop (the distance where the transit stop is visible from the building). This number almost halves beyond this distance (O’Sullivan and Morrall 1996; Daniels and Mulley 2013).

Furthermore, the visual experience of urban space includes sequences of viewsheds (Cullen 1961, 1967) of individuals and groups (Figure 2c). Visual perception changes when the observer is alone or in a group. Individuals actively observe urban spaces or shift to minimal visual perception when they reflect or relax. If an individual is in active observation mode, blind parts of the isovist often cause inconvenience (Figure 2c1) that often trigger retreats (Figure 2c2). Visual perception is at minimum, or activates occasionally, when walking or talking in a group (Figure 2c3).

Visual proximity and commercialization of buildings

Visual proximity is crucial for the commercialization of buildings adjacent to transit stops. Commercialization around transit stops is closely associated with pedestrian movement (Figure 3a). The paths of arriving and departing passengers converge on and disperse from transit stops. Businesses tend to locate within the viewsheds and hearing ranges of pedestrians and transit passengers. If a person steps out alone from a bus or train, an individual viewshed opens (Figure 3a1). If an individual joins a group in movement, the vantage point can move across urban space. The mode of observing space emerges later as the urban space elongates and encompasses several vantage points, one for each member of the group (Figure 3a2). Transit and commercial activities form a virtuous circle. Transit, depending on the level of service, attracts crowds of passengers that are potential customers. More traffic and passengers attract more surrounding businesses. Established commercial storefronts and entrances to public buildings along pedestrian paths create a pattern of public spaces in visual proximity to transit stops (Figure 3a3).

Figure 3. Visual proximity, pedestrian flows and commercialization

The commercialization pattern also depends on the flow of pedestrians (Figure 3b). Transit vehicles can carry many passengers and high patronage can produce crowds of people that wait at platforms or walk to and from transit stops and are potential customers (Figure 3b1). The location of the transit stop can be peripheral to the main streets, commercial strips and pedestrian flows (Figure 3b2). The commercialization is an incremental transformation process of buildings to open their façade to the street (Davis 2009; Narvaez, Penn, and Griffiths 2015). Sound is equally important for commercialization and it reinforces visual perception. According to Gehl (1987), the hearing range is up to 30 m (Figure 2b). Within this hearing range, it is possible to detect the voices of market vendors. In streets and squares wider than 30 m, it is possible to see and recognize individuals, but it is not possible to decipher their speech. The sounds are perceived as a background buzz that arguably creates a discontinuity in the public space pattern.

Methodology

To analyze public space patterns around typical transit stops, nine neighbourhoods were selected in three Swedish cities. The neighbourhoods include several typical transit stops with a wide range of commercialization and public space patterns around many transit stops in different stages of evolution. The public transportation system typology derives from study visits and observations around the world (Figure 1). Gothenburg and Norrköping have a network of tramways operating on streets. Stockholm has an integrated metro system, a system of completely or partially segregated suburban railways and a commuter rail system. Two new neighbourhoods, Hammarby Sjöstad in Stockholm and Lindholmen in Gothenburg, unfold along partially segregated Light Rail Transit (LRT) or Bus Rapid Transit (BRT) systems. BRT is often referred to as Buses with High Level of Service (BHLS) in a European context (Heddebaut et al. 2010).

The method includes mapping of the commercial and public space patterns around transit stops followed by morphological abstractions of these patterns. To analyze the publicness of urban spaces, this research adopted a skewed top perspective representation. The skewed top perspective visualizes the interaction between the street as space and the orientation of building façades to the street (Jacobs 1961; Caniggia and Maffei 2001 [1979]). If the street space is surrounded by buildings open to the public (commercial storefronts, institutions, and so on) it is mapped as public space. Figures 4 and 5 present the the detailed methodology to analyse three-dimensional interactions of building façades and streets and to create a map of two-dimensional shapes of public space patterns.

Photographs and graphical illustrations from Stora Torget, a square in Stockholm are shown in Figure 4a and 4b. Perspectives or images (Figure 4b1), plans (Figure 4b2) and elevations are common three- or two-dimensional representations of urban spaces. To combine these representations the proposed skewed top perspective reveals building elevations in the plan view (Figure 4b3). This two-dimensional urban space envelope shows streets, squares and tilted building façades. It is a 3D background presented as 2D drawing board. This representation allows for the visualization and analysis of urban design elements (interaction between the building façade and the street space) in the plan view similarly as a building story in Building Information Modelling (BIM) software.

Figure 4. Perspectives and representations of urban space

The two-dimensional representation of building façades (Figure 5a1) allows to map their degree of publicness (from completely public to completely private). The private, semi-private, semi-public or public character of building façades are presented with graduating colours (Figure 5b1) to illustrate the varied public or private character of the square as urban space (Figure 5b2). This varies from yellow public spaces to dark green private spaces. The interaction is formulated as: Public street + Semi-public building façade = Public-semi-public space. Figure 5c shows the shape of a surveyed public space in plan view. The yellow shape designates enclosure between publicly accessible building façades, commercial storefronts and public buildings. The yellow colour is used consistently in this paper to emphasize enclosed public spaces.

Figures 4 and 5 present the detailed methodology to analyze three-dimensional interactions of building façades and streets and to create a map of two-dimensional shapes of public space patterns. Figure 4a illustrates the methodology of mapping public spaces around typical transit stops, a tramway on street in Norköpping and a partially segregated busway in Gothenburg. It identifies and highlights urban design elements such as commercial storefronts and building façades through photographs and shows TOD patterns of public spaces in plan view with overlays of viewsheds (100 m radius) from the transit stop. Figure 6a1 illustrates public and semi-public spaces with different colours.¹ Building façades with commercial storefronts are dark blue, apartment buildings are light blue, and commercial storefronts that interact with the public street to create public spaces are yellow. These yellow public spaces are presented on the maps as yellow 2D polygons (Figure 6a2). The polygons illustrate commercialization and public space patterns as well as three-dimensional spaces enclosed with commercial storefronts or public buildings. The influence of the commercial storefront on feelings of enclosure is considered in a context of a hearing range of approximately 30 m. This roughly corresponds to the size of an historic square developed for public speaking and market vending (Figure 2b). If there is only one shop with a commercial front and the distances between the buildings is greater than 30 m, the public space shape takes a triangular form. If there are two shops opposite one another, the shape is rectangular or trapezoidal. This is illustrated all along the busway in Gothenburg and in Norrköping where the main street (Drottninggatan) embodies a large open space.

Figure 5. Methodology of mapping public spaces

Figure 6. Method to survey and mapping publicness of urban space around transit stops in Norrköping and Gothenburg and create abstractions of TOD patterns of public spaces

The maps of the actual patterns of public spaces in the Swedish cities are complemented with abstractions about TOD patterns for typical transit stops (the typology shown Figure 1). Abstraction is a morphological method to recognize and generalize typical or representative elements and patterns (Marshall and Çalişkan 2011). Abstraction is used to derive a typical exemplar or prototype of a building, street, city block, neighbourhood, and so on. It is common to identify representative examples. The representative examples of buildings are illustrated with building plans or elevations and through a detailed inventory of architectural elements (Sanders and Woodward 2015) or described through photographs, diagrams and plans of representative buildings (for the case of shopping malls, see Southworth 2005). Abstraction in this research includes the identification of representative examples from various patterns of public spaces in visual proximity to typical transit stops. The abstracted shapes of TOD patterns of public spaces in the Findings section are representative of completed processes of commercialization (Figure 6b).

Findings

The findings are presented as maps that illustrate the overlay of public space patterns around the typical transit stops with viewsheds of 100 m radius from the transit stop platform or station exits. The TOD patterns of public space are marked in yellow to designate the urban spaces surrounded by commercial storefronts of buildings and public buildings. Figures 7a3–d4 are morphological abstractions of TOD patterns of public spaces around typical transit stops.

Figure 7a presents commercialization patterns along public transportation routes. Figure 7a1–a2 shows the commercialization patterns along two main streets, Drottninggatan in Norrköping and Linnegatan in Gothenburg. These transit corridors are historical and emerged before the advent of the automobile. On these main streets, the commercial storefronts continue between the stations along the streetcar lines. The side streets are usually lined with apartment buildings with semi-private façades. The side streets do not attract commercial activity streets beyond the viewsheds. The storefronts sometimes continue along the side streets and this is more common near the intersections adjacent to transit stops. The streetcars in Norrköping and Gothenburg produce elongated TOD patterns of public spaces (Figure 7a3) where public transportation service is very slow. It is often easier to walk to the next station than to wait a few minutes. These pattern abstractions correspond with commercialization patterns along the main streets in Norrköping and Gothenburg. However, they are different to the circular walkshed and the commercialization patterns that seldom extend beyond the viewshed of transit stops.

Figure 7a. Results of the analysis of the TOD patterns and morphological abstractions

Figure 7b. Results of the analysis of the TOD patterns and morphological abstractions

Figure 7c. Results of the analysis of the TOD patterns and morphological abstractions

Figure 7d. Results of the analysis of the TOD patterns and morphological abstractions

The analyses of the public spaces along completely segregated railways and busways (Figure 7b) show dislocated TOD patterns, such as the old commercial core around Älvsjö station (Figure 7b1). The public spaces or commercial storefronts often partially surround the viewsheds from the station exits as in Salsjöbaden station (Figure 7b2). The completely segregated railways and busways act as physical barriers (if on the ground) or psychological barriers (if elevated) in urban space. There are different three-dimensional urban design solutions to integrate elevated and completely segregated transit stations. If the transit station is a major node, it is common to incorporate the station into a building, usually a shopping mall (see Loukaitou-Sideris et al. 2013). Completely segregated railways and busways allow for high-speed public transportation. The results show that, depending on the number and configuration of exits, amoebic patterns of public spaces are created and start at the station exit. The abstracted TOD patterns of public spaces are circular or amoebic but are dislocated from the centre of the transit stop in contrast to the circular walkshed (Figure 7b3). The abstracted patterns do not correspond to the walksheds. Instead, they are much smaller and seldom extend beyond the viewshed from the station exit.

In underground public transportation, subways are fully segregated systems that create no relevant barriers in urban space. Here, TOD patterns have a circular and amoebic shapes at each exit. These rings are often superimposed onto a wider ring. In the case of the two subway stations in Stockholm, there is also an overlay of elongated TOD patterns originating from historical omnibuses and tramways (Figure 7c1, c2). The abstracted TOD patterns include constellations of superposed rings. These shapes are closest to the standard walkshed ring (Figure 7c3).

The TOD patterns along the partially segregated LRT systems in Stockholm (Figure 7d1, d3) and BRT/BHLS in Gothenburg (Figure 7c3) are elongated and fragmented. The partially segregated railways and busways act as permeable barriers in urban space and are in different stages of evolution. The TOD patterns in Stockholm present a case of full (Figure 7d1) and partial commercialization of the ground floor of the buildings (Figure 7d3). The tramway along Nynasvagen, in Enskede, Stockholm does not exist today, but the commercial storefronts are still in place. Initial phases of commercialization are visible in the Gothenburg example along Östra Eriksbergsgatan, where there are only a few shops at the corners of buildings (Figure 7d2). This evolution corresponds to the proposed TOD pattern abstractions (Figure 7d4). As with public transportation on streets, pedestrians move in the direction of trams and buses with little commercial activity on side streets. Commercialization happens gradually in the adjacent buildings and within the viewsheds of the transit stops.

Discussion

The findings show incremental commercialization as a gradual process involving different stages. The public spaces fill in sections of the viewshed and surround the transit stop (Figure 7b1, b2 and d2). The TOD patterns of public spaces form amoebic shapes and sometimes expand beyond the viewsheds (Figure 7a1, a2 and d1). Traces of this incremental commercialization exist even when the public transportation is defunct (Figure 7d3). The evolution of commercial and public spaces expansions is arguably a consequence of more or less intensive pedestrian movement to and from the transit stop (Figure 3b). The elongations and amoebic shapes of the TOD patterns of public spaces in visual proximity to transit stops (Figure 7a3–c3 and d4) deviate significantly from standard TOD rings, both in size and form. The commercialization is usually limited to the 100 m viewshed to the transit stop. These commercial cores remain even when the public transportation is defunct.

This research emphasizes the evolutionary aspect of commercialization around transit stops as a way to integrate public transportation systems and design for TOD. This integration assumes urban design processes of incremental development and the creation of commercial centres (Alexander et al. 1987). Instead of focusing on representative examples and illustrating complete commercialization around typical transit stops as is commonplace in morphological studies (Southworth 2005; Sanders and Woodward 2015), the results represent multiple cases of commercialization patterns in different stages of evolution. If only one transit stop is analyzed in detail, it is not possible to identify variations in the shapes. Urban designers then simply infer ideal commercialization patterns based on an abstracted typology of representative TOD patterns of public places, instead of understanding the processes of commercialization. The incremental processes behind the emergence of the form are more important than the form of TOD patterns (Scheer 2010).

Buses, trams and trains are the densest mobile public spaces places in the cities. To maintain visual continuity in urban experience, transit stops should be surrounded by public spaces and commercial storefronts. Passengers are not comfortable waiting in public spaces with no commercial activity. TOD patterns with public spaces are more welcoming for transit passengers. They are arguably the most effective zones for TOD due to visual proximity and commercial activity and pedestrian movement continuously shapes them. Urban designers can work with these amoebic shapes to harness the multiple benefits of public transportation. The TOD approach to creating public spaces can be used to integrate even the smallest bus stop by catalyzing commercialization in surrounding buildings. To date, architects and urban designers have largely focused on major train and bus stations in TOD design guidelines (e.g., Calthorpe 1993).

This study produced a typology of representative TOD patterns of public places that must be considered critically. The results do not always show commercial activity (see one of the transit stations in Figure 7b2). This typology illustrates a completed process of creating commercial storefronts and opening building façades that are in visual proximity to transit stops. The typology of representative TOD patterns of public places can be used in urban design practice. The commercial storefronts are typically included in the building ordinances of FBCs. Urban designers must consider specific local conditions when they apply the TOD pattern typology. In TOD, there is a convergence of both elements of public transportation, including (1) elements and patterns of urban form, and (2) interfaces between the transit stop to the street, the street and the building, and so on. Their interaction creates diverse contexts and patterns. Alexander, Ishikawa, and Silverstein (1977) argue that each city has a distinctive set of patterns. Commercialization patterns must relate to city-specific patterns. Acknowledging this, the city and the transit stop can grow organically. Here, it is important to note the tensions between the private automobile and public transportation as mobility cultures. Public transportation has a sentimental role in European neighbourhoods and cities that grew historically and developed along routes for buses, trams and trains. This nostalgic culture of public mobility is not as prominent in other parts of the world.

This paper proposes a morphological methodology for analyzing public spaces as a process of commercialization which is important for integration with public transportation. Businesses tend to locate in places with pedestrian activity and through the use of transit, pedestrians converge to and disperse from transit stops. Every transit stop is a smaller or larger urban node that attracts potential customers for businesses. In the methodology and the skewed top representation that informs the survey and analysis, the definition of public space is simplified and is based on a morphological interpretation of urban space (Krier 1983; Caniggia and Maffei 2001 [1979]; Kropf 2011, 2014). The proposed method focuses on physical settings such as commercial activity and storefronts, public buildings and spaces. Qualities such as place identity, image, ownership, maintenance, comfort, and so on (Canter 1977; Montgomery 1998; Mehta 2014) often redefine what is private, semi-private, semi-public or public. There are quasi-public spaces that can be privately owned, such as townscape malls (Southworth 2005).

This research proposes a new representation of streets and street spaces. Many urban designers come from the architectural profession and focus on buildings, more precisely the design of buildings without designing building (Walters 2007). This is incorporated in coding and FBCs as a representation of a typical plot and a typical building. The underlying element of urban form is not the building on the plot but the street (Conzen 1960; Caniggia and Maffei 2001 [1979])). The street space and its interaction with surrounding buildings is an important urban design scale that has no representation to work with. Kropf (2014) discusses these two different views of the city block. The city block is a three-dimensional street space with surround buildings instead of a city block of conjoined plots and buildings (Caniggia and Maffei 2001 [1979]). The top skewed perspective that includes building façades visualizes the interaction of the street or square and building façades to visualize this morphological perspective. This representation of street spaces is conceived as a design space, an analogy to the building storey in Building Information Modelling (BIM). The building storey in BIM is a drawing board where different building elements (walls, windows, doors, furniture, and so on) are juxtaposed. The top skewed perspective can be a drawing board for urban designers, similarly as a building plan is for architects. It can act as a background to play with design elements in the viewshed. There is no consensus among urban designers about which design elements make street space and how to represent them. Many urban designers use building elevations to analyze public spaces (e.g., Appleyard 1981; Mehta 2009), but not in the context of a top perspective and sequential visual perception (serial vision, Cullen 1961, 1967). These representations of street spaces and sequences of viewpoints can be integrated in generic 3D modelling software through BIM. Urban planners and designers currently use two-dimensional Geographic Information Systems (GIS) and Computer Aided Design (CAD) software, but the integration of transit stops with cities and the analyses of public spaces adjacent to transit stops requires 3D software.

Ultimately, the typology can help TOD researchers to analyze proximity to transit and with integration to public transportation. They can focus on trip generation rates and urban design parameters within the viewshed and its commercial core. They can compare these parameters with the wider walkshed or within the area of maximum walking distances. Some passengers walk up to 2000 m to reach a transit stop (Daniels and Mulley 2013; El-Geneidy et al. 2014).

Conclusions

This paper demonstrates how commercialization and public space patterns, illustrated by Calthopre (1993) as commercial cores, emerge and expand around typical transit stops. The results show that TOD patterns of public spaces in visual proximity to transit stops are very different from the areas defined by the standard walking radii (Figure 7). These amoebic or elongated shapes are influenced by transit stop type and other physical settings such as street layout, commercialization, orientation and openness of building façades, and so on. They are small overlaid corridors within a viewshed and elongate when commercial activity creates intensive pedestrian movement to and from the transit stops.

TOD as a policy in European cities aims to redesign entire metropolitan areas to integrate with public transportation systems (Bertolini, Curtis, and Renne 2012). This includes not only major train stations, but also small bus stops. Urban designers have to approach this problem first from a perspective of visual proximity. With this alternative approach to TOD and the integration of public transportation, every transit stop has the potential to create a commercial core within a 100 m visual range. Urban designers working with TOD should focus on the viewsheds and composition of urban design elements that can facilitate flexibility in processes of commercialization. Depending on the type of transit stop, the level of transit service and arrangement of public spaces around the transit stop, these public spaces around transit stops (referred to as commercial cores by Calthorpe) can expand into local corridors or a sequence of regional transit nodes via a comfortable ride on a bus or train. Using visual proximity to inform TOD and the arrangement of urban design elements to create public spaces around transit stops can be as important as placing transit-friendly land uses (shopping, offices, and so on) in TOD walksheds.

To analyze visual proximity and the integration of public transportation with cities, this research proposed a top skewed perspective. Urban designers can use this representation for analysis and practice. Urban design practitioners can create FBCs that visualize the interaction of the streets or square with surrounding spaces, not just the elevations and the street. In the two-dimensional top skewed perspective, different architectural, landscaping and urban elements such as commercial storefronts can be juxtaposed. Commercial storefronts are a common urban design element described in FBCs. The integration of the transit stop as a loading platform on the street or station exit can be represented as a sequence of viewpoints in the top skewed perspective (see Figure 4) to illustrate commercial activity on building façades. This representation of street spaces is conceived as a design space. The skewed top perspective delimits this representation to visual perception and elements that are visible on the building façade, but it can be used in practice to represent cities, especially when working with experiential qualities of squares and street spaces (Appleyard 1981; Mehta 2009; Lee and Talen 2014).

In the end, TOD patterns of public spaces in visual proximity supplement rather than replace walking radii, but they are arguably more important for integrating public transportation in cities. Within the zone of visual proximity to a transit stop (100–200 m), the generation of passengers is arguably at its maximum. This paper puts forward a tentative new hypothesis for transit researchers. Further research in public transportation is needed to confirm the conclusion that the viewshed matters more than the walkshed. Another direction of future research would be to study pedestrian movements around typical transit stops to understand how this influences commercialization patterns in different types of neighbourhoods. A third direction of research would involve the development of new software to integrate generic 3D modelling with old and new representations, toolboxes and methods in urban design practices. This would include conceptual research as well as software development.

Acknowledgments

This research was supported by Riksbyggen’s Den Goda Staden scholarship, Swedish Innovation Agency Vinnova. Thanks are due to Andrew P. Karvonen, Tigran Haas, Karl Kottenhoff and Paul L. Casey.

Disclosure statement

No potential conflict of interest was reported by the author.

Additional information

Funding

This work was supported by the VINNOVA [2009-01233,2015-03483]; Riksbyggen [Jubileumsfond Den goda staden]; Energimyndigheten [2017-003267].

Notes

1. The figures are shown in colour in the online article. In the print version, dark blue, light blue and yellow correspond to dark grey, mid grey and light grey.