As footbridges constructed in urban environments typically experience the greatest pedestrian and cyclist traffic due to the density of the surrounding population, these structures serve as accessible benchmarks of current solutions to spanning obstacles that might otherwise disrupt the connectivity of the city pedestrian and cyclist network. Accordingly, a collection of footbridges in populous cities in Italy, Spain, France, England, Scotland, and Canada were chosen as case studies for evaluating the elements of footbridges constructed in city environments that could inform exceptional bridge designs that restore and improve urban infrastructure. A firsthand survey of these footbridges was conducted by accessing these footbridges as a pedestrian and, when viable, as a cyclist to assess these metrics from the user’s perspective. An assessment of the structural and aesthetic components of these footbridges as well as their state at the time of visiting were presented in this report to provide a personal perspective on the properties of footbridges that contribute toward successful and unsuccessful integration within the surrounding urban environment. A discussion of the lessons learned through these on-site visits and evaluations is provided in this section.
Establishing the term accessible as a metric of exceptional bridge design relies on two definitions: global versus local. In the global sense, accessibility pertains to the development of a traversable design for persons with disabilities as well as the practical placement of a footbridge within an urban pedestrian and cyclist transportation network. In the local sense, accessibility pertains to the ability to directly interact with the structural and nonstructural components of a footbridge. While global accessibility is fundamental to the successful integration of a footbridge within an urban fabric, the local accessibility of individual footbridge components to the user can be perceived as the provision of a blank canvas. Assessing the damage present during the on-site visits helps define aspects of footbridges detrimental to the desired aesthetic.
In serving as tangible support for the user when traversing a bridge, railings are typically the most accessible footbridge components and, as such, were found to be the most susceptible to damage. Graffiti, stickers and sticker residue, scratches, cracked or shattered glass, and locks were found to be the most common culprits of damage to footbridge railings. While graffiti can be viewed as an aspect of local expression, the presence of graffiti on a footbridge can deter use of the crossing if it is perceived as an unsafe environment while also tainting the intended bridge aesthetic. Counteractive measures can be taken by applying anti-graffiti coatings to susceptible surfaces or installing passive measures such as security cameras. Although painting can be argued as an expensive maintenance requirement, the preservation of an aesthetic can encourage use of the bridge and prevent deterrence due to a damaged aesthetic.
While the caveat to the tangible accessibility of footbridge components is the provision of a blank canvas, the components containing extensive amounts of graffiti were typically ones in accessible, yet out-of-sight locations; e.g., abutments, piers. As a result, there is a default to less conspicuous methods of defacement, such as stickers and scratches, on well-monitored footbridge components; even options such as the placement of locks is part of a socially acceptable norm of romantic gestures and not viewed as detrimental to the structure. While locks may appear to be harmless, an accumulation can add an unexpected load to the railing and damage the components to which they are attached; in addition, locks can obscure the desired transparency of a bridge railing.
Given the likelihood of damage to footbridge railings, panelization provides easy to install and readily replaceable railing systems; although repetition can be viewed as monotonous, variability can be achieved via the material choice for the protective panel elements. Steel mesh, perforated plate, cable, and traditional horizontal rod or vertical plate systems can vary from the transparent to the opaque; while the type of obstacle spanned may dictate the height of the railing, an element of play can be achieved via patterning, orientation, and form. While glass provides the greatest transparency and gives the illusion of slenderness by isolating the railing component from the bridge deck, it can yield the greatest maintenance burden. In terms of efficiency, integrating the railing with the superstructure not only yields a cohesive aesthetic but also can lead to a reduction in superstructure depth to achieve a slender footbridge form.
As a pedestrian, typically one can only comprehend the global structural form of a footbridge when viewed from an adjacent bridge or sidewalk. When the structural system disappears into the urban fabric, the tangible aesthetic is the railing, which can add character to an otherwise unseen urban infrastructure. As skybridges provide an aboveground pedestrian network, their impact on the urban aesthetic is unavoidable. The logistical necessity of sheltering the pedestrian from the environment should not adversely affect the user experience within the skybridge by imposing a feeling of enclosure. As glass is the default material for defining the environmental barriers, the choice of color, flooring, and structural system can contribute to an open internal atmosphere. The integration of barrier and structure can reduce the opacity caused by the juxtaposition of mullions and structural elements. Indoor pedestrian comfort prescribes the use of heating, ventilation, and air conditioning systems to create a space usable year-round; these systems can either remain exposed or contained within a dropped ceiling, which may augment the sense of enclosure. Whether skybridges should integrate into the surrounding urban aesthetic imposed by the buildings to which they connect or conspicuously stand out, a sense of play can be established in the two environments they define, external and internal, via structural form, materiality, and color.