Save this picture! Margaret Hunt Hill Bridge, Dallas, Texas. Image © Greig Cranna

Increasingly close collaboration between architects and engineers has caused an explosion in bridge design over the last few decades, resulting in structures that are both bold yet rational. As a result, cities have exploited bridges as great monuments of design, to foster pride in the residents and promote themselves as a destination for tourists. These ideas have inspired photographer Greig Cranna as he travels the world, capturing the elegance of today's bridge infrastructure.

Cranna has been documenting some of his stunning photography on Instagram, collating it over the past 20 months into a forthcoming book, Sky Architecture—The Transformative Magic of Today's Bridges. In capturing these entrancing structures, the photos show the impact of the bridges as an addition to the landscape and revel in their contemporary silhouettes and designs.

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26 Degrees in Calgary yesterday, but irresistible skies, irresistible bridge. #CalgaryAlberta #PeaceBridge #SantiagoCalatrava #BowRiver #SkyArchitecture #TheBridgeProject #YYC A post shared by Greig Cranna (@crannaphoto) on Oct 28, 2017 at 9:57am PDT

Bridges began their life as simply a safe crossing for those on foot, and later went on to bear horses and carriages. With relatively minimal loads, the focus of the designs could be spent on the overall appearance. Take the ornamentation of the 16th century Rialto Bridge in Venice for example; its human scale design allowed for an experience of grandeur, creating an architectural icon.

Save this picture! East Bay Bridge, San Francisco, Ca. Image © Greig Cranna

At the turn of the 19th century, industrialization and the invention of the railway demanded bridges with much larger spans to be built that could handle the greater loads. The need for stronger connections between cities led to the emphasis being shifted to the structural qualities of the bridge and aesthetics were arguably forgotten. At this point, bridges were primarily built out of steel for greater structural support and appeared utilitarian in their look. Forth Bridge in Scotland demonstrates this engineering triumph, with its multiple cantilevering sections covering a span of over half a kilometer.

Today, bridges see much more involvement of architects in their designs. Now more than ever, improving technology has enabled explorations of form and granted opportunities to experiment with structure. The power of bridges to influence people's perceptions of a place has not gone unnoticed by cities as they are "branding themselves around signature structures," explains Cranna.

Society's reliance on transportation has provided us with famous landmarks in the past such as the Brooklyn Bridge, Golden Gate Bridge and Sydney Harbour Bridge that instantly are associated with the location they belong to. These days, bold design is a requirement for contemporary bridges to stand out in the same way to become a recognizable structure.

These distinct forms are apparent in Cranna's photographs; however, it is the pedestrian bridges that he finds most interesting. Harking back to the early stages of the bridge, they are much more personal and human-scale, creating an individual experience going from A to B. As well as the interaction with people, pedestrian bridges present an environmental advantage, encouraging a greener approach to travel.

Among the pedestrian bridges photographed by Cranna is the BP Bridge in Chicago. Designed by Frank Gehry, it takes you on a winding journey between two parks and across a road. The serpentine path is deliberately curved to provide a longer, gradual ramp for the bridge to be accessible to all and the broad form acts as an acoustic barrier from the road below. This attention to the human senses and how we perceive such a space is an architectural quality that can only be achieved on infrastructure at this personal level.

Save this picture! Gateshead Millenium Bridge, Newcastle-On-Tyne, England. Image © Greig Cranna

Cranna has also photographed Gateshead Millennium Bridge, designed by Wilkinson Eyre Architects, that responds to the need for pedestrian crossings over the River Tyne in Newcastle, England. The tilting bridge has become an iconic attraction, drawing crowds to watch the dynamic structure move like a blinking eye for larger boats to pass. Unlike the BP Bridge, its minimal design is lightweight and allows views up and down the river as an integral part of the experience for the users.

As pedestrian bridges emerge across the world, the way in which they respond to the human senses has led to the more playful forms. Besides those photographed by Cranna, we can see abstract shapes appear in Lucky Knot by NEXT Architects, which creates viewpoints across the landscape, and in RDG Planning & Design's High Trestle Trail Bridge, whose whimsical tunnel of blue lights transforms the space at night.

Save this picture! Bond Bridge, Kansas City, Mo. Image © Greig Cranna

Although there is still an obvious demand for larger infrastructure to handle vehicles, it is important that we continue this evolving passion for pedestrian bridges. We now see bridges not only as a method to cross roads or rivers but as a sculptural piece of technology that people want to visit and experience. The emphasis on bridges that can improve pedestrian transport has benefits both environmentally and for the tourism industry, so it is important that we continue to create these spatial and sensual experiences—and welcome that such developments are cataloged and celebrated by photographers such as Cranna.