The perceptual morphology of public spaces – Extracting urban design factors of streetscapes that support walkability and Transit-Oriented Development (TOD)

Abstract

Automobile travel consumes scarce resources of fossil fuels and is a major cause for accelerating climate change globally and air pollution locally. The sustainable mobility problem of automobility lies in the development of car-dependent suburbs in the 20^th century. Many neighbourhoods were designed specially to support individual mobility and private cars. Consequently, walking and cycling is impossible in these neighbourhoods (Southworth, 2005) and public transport is uncompetitive to the automobile. Furthermore, the bus stops are typically on the edges of the suburbs often isolated along motorways and car-dominated streetscapes. Transit-Oriented Development (TOD) is a development alternative to the suburban car-oriented model that seeks to redevelop car-dependent suburbs and streetscapes into eventful urban environments that will provide a pleasant walk to public transport stops. TOD includes the aspect of (land use) development and orientation to public transport. Walking distances conventionally define service areas for public transport and urban growth boundaries for TOD. Urban designers accordingly draw rings around transit stops and arrange transit-supportive land uses within 10-minute walksheds. The walking distance approach to TOD neglects processes of creating public spaces and integration of public transport stations based on visual proximity and urban experience (Stojanovski, 2020). A new urban development might be within a walking distance of 800m (as a 10-minute walk), but it might be impossible to walk because of unpleasant streetscapes and road barriers. Often wide roads and open spaces act as walkability obstacles to public transport stops.

This paper reviews urban design theory and the literature on urban design factors of streetscapes that support walkability and TOD. The urban design factors are based on morphological research and urban design theory, that derives from older urban design classics such as Gordon Cullen (1961) and Jane Jacobs (1961) to a more recent classics on walkability (Ewing & Handy, 2009; Mehta, 2009; 2014). Factors include the sidewalk design (as sidewalk width) in relation to street width and pedestrian flows. The sense of enclosure is another urban design factor, calculated as the relationship between building heights and street width, as well as presence of greenery. The third set of factors tangle edges, barrier effects and permeability, that create a certain feeling of axiality (pressure to move) and convexity (nodal perception of stopping and looking around) (Hillier & Hanson, 1989). The literature review focuses also on street frontage analyses and factors such as building setbacks, commercial storefronts, orientation, and rhythm of entrances, etc. (Talen& Jeong,2019).

The paper aims to inspire a debate on public space and perceptual factors in the TOD framework. The extracted urban design factors of streetscapes and public spaces will be further researched with walkthroughs and the results will be compiled as design guidelines to transform streets and neighborhoods and improve walkability and access to public transport. There is extensive research on Form-Based Codes (FBCs) and design guidelines in planning practices (Carmona et al, 2006; Carmona, 2009; Talen, 2009; 2013) and the paper aims to enrich the original TOD guidelines published thirty years ago (Calthorpe, 1993) with accent on public spaces and streetscapes.