When we think of urban sprawl, our imagination tends to go outwards and upwards. A ring of skyscrapers circling the downtown core, perhaps, or a sea of suburban townhouses off the freeway.
Rarely do we think _downward_s: about the intricate webs of pipes and cables that lie beneath our sidewalks. These unseen networks power our cities, connect our telecommunications, and carry away our waste. But like so many of our cities’ above-ground features, they weren’t always designed strategically. Underground infrastructure tends to be built on an ad-hoc basis—as telecommunications technology developed, we’d lay down a new wire—and when the company responsible for putting it there eventually merged, restructured, or went out of business, their data was buried along with the wires.
All this hidden infrastructure has become a logistical nightmare as we now seek to modernize our cities’ transit systems. Case in point: When a transportation company started digging its first tunnel in a Los Angeles suburb last fall, it had to clear it with the 19 utility agencies that might have lines in the area. One wrong dig and they might have left an entire neighbourhood without power, or started spewing raw sewage into the streets.
The longtime industry standard has been to use electromagnetic tools to locate wires and other conductive materials. It’s a great system for identifying metals, but useless at seeing non-conductive pipes made of concrete, clay, or plastic. According to the Damage Information Reporting Tool’s 2016 report (the most recent year that data was available), the number of incidents in the United States and Canada submitted were 390,366, and amounted to nearly $1.5 billion worth of damage.
New tools have emerged in recent years that can prevent these pricey mistakes. Thanks to the subterranean mapping system ground-penetrating radar (GPR), geographers, archaeologists, and city planners are rediscovering the rich human history buried under our feet. Just a handful of the recent finds credited to GPR technology include a labyrinth of tunnels under Rome and man-made caves under Nottingham. Almost 60 massive stones located underneath Stonehenge suggest that the iconic monument was once part of a much larger structure.
GPR technology is similar to what’s used by MRI machines. It emits high-frequency, non-invasive radar pulses that can penetrate rock, soil, ice, and water to create images of the subsurface. GPR isn’t exactly new—it was first patented back in 1910, and bulky hand-held devices have been around for decades—but its level of detail, accessibility, and affordability has seen rapid gains in recent years, as has the power required to process the immense amounts of data it generates and to create 3D visualizations. Today’s GPR can now create detailed maps of underground pipes and cables that previously couldn’t be viewed without digging. This saves a ton of money for developers and minimizes traffic disruption. Plus it could prevent grim discoveries, such as the 4,000 plague-ridden skeletons London construction workers found in 2013 while digging around a transit line, by analyzing an environment before human workers get involved.
Even if a newish city doesn’t have a decrepit tangle of old sewage pipes or plague victims under its streets, it can still benefit from doing a GPR deep dive. “The world is always changing, and what happens underground greatly impacts what happens above ground,” Stuart Woods, vice president of geospatial solutions at Leica Geosystems, told Informed Infrastructure. For example, changes in an area’s soil density could elevate roads (compromising our navigation systems and impacting large-scale infrastructure planning) or shift the position of our underground utility pipes (affecting our subways and hypothetical hyperloops). Mexico City is famously sinking, as is New Orleans, and these geographic shifts could cause significant damage to the cities’ transit systems without preventative measures.
GPR isn’t foolproof. It struggles when exposed to soils that are high in salt content, has a high energy consumption, and requires well-trained professionals to analyze and organize the data. But perhaps the biggest barrier to GPR’s success has been convincing people to share their findings. Municipalities, utility providers, and private companies are often protective of their data out of fear of competition and privacy breaches, while on the opposite side, groups such as the Open Geospatial Consortium have sought to make quality open standards for the global geospatial community.
One solution to this conflict between public safety and personal privacy arrived through tragic circumstances. In July 2004, Belgian construction workers accidentally ruptured a high-pressure gas pipeline near the port town of Zeebrugge, killing 15 people and injuring hundreds. In response, the government created a massive underground infrastructure map depicting every asset owned or controlled by more than 300 utilities in Belgium’s Flanders region. As reported in Bloomberg, this amounted to almost 400,000 miles of subterranean cables, pipelines, wires, and conduits that could circle Earth 16 times. To prevent unauthorized use of this underground infrastructure map, contractors in Belgium now must submit the coordinates of their work environment to a computer portal, which then relays the request to every organization with infrastructure in the area to determine if the dig could be dangerous.
Belgium’s solution seems intuitive and harmless, but it connects to a broader, often heated conversation around what kinds of information we should be collecting about our cities, and who should have access to it. "Smart cities is a very double-edged concept," said Lee Tien, senior staff attorney at the Electronic Frontier Foundation, told the Chicago Tribune. "The idea is to capture more data and utilize more data about what's going on in a city. By definition, unless you exclude people, that is the same as conducting more surveillance."
A 17th-century plague victim doesn’t have much of an expectation of privacy, but underground surveillance could affect how we move through our subterranean transit networks. Given the risks associated with blindly digging downwards, however, it’s a problem that could definitely benefit from a little more conversation, and a lot less action.