What Makes a City Sustainable Anyway?

Author: Dominique Bonte

More than 70% of global carbon emissions come from cities, making metro regions the starting point for decarbonization. The four main areas that cities must focus on to reach “sustainable city” status are the energy grid, building infrastructure, transportation, and waste management. To get there, city planners and technology vendors must work side-by-side to tackle the complex question of how to reach net-zero emissions. They should also pay close attention to the sustainability case studies stemming from other cities to gain inspiration for future projects.

Defining a Sustainable City 

A sustainable city is a city built with environmental friendliness and decarbonization at the forefront of infrastructure and governance decision-making. The practices that are put in place are meant to serve the city in the long term. Getting to this point doesn’t happen overnight; it requires considerable technological investment and collaboration with other organizations, such as nonprofits, charities, and public companies motivated by social causes. When a city is sustainable, its Greenhouse Gas (GHG) emissions are low, or even net-zero, and air quality is free from contamination. But to make a city more sustainable, urban planners must change the way they think about energy, building infrastructure, transportation, and waste removal processes.

Make Energy Consumption More Green

Although most cities don’t have full control over the energy grid, there are a handful of ways to reduce greenhouse gas emissions associated with urban energy consumption. For starters, smart meters can be deployed throughout a city as a means for utilities to optimize the grid and for customers to see real-time consumption data, prompting them to change lifestyle habits that hurt the environment.

The supply chain disruptions caused by the COVID-19 pandemic showed city officials that they must be more self-sufficient and less reliant on a single source or energy supplier. Just like an investor may diversify a portfolio, a sustainable city will diversify its “energy portfolio”—by adding renewable energy sources like solar or nuclear, in addition to and eventually replacing fossil fuels with 100% green energy.

Smart streetlighting is a common decarbonization tactic in cities that want to be more sustainable, as it’s a well-proven tactic. Besides being 30% more cost-effective compared to Light-Emitting Diode (LED) lighting, smart streetlights serve as the point of deployment for other technologies like sensors and Electric Vehicle (EV) charging stations, and also act as a base of communication for network and radio protocols.

Re-think Urban Development

Reducing reliance on carbon materials is one great way to decarbonize a building, but there are a handful of other strategies that should be used to make a city more sustainable. Some of these strategies include using digital twins, leveraging district heating schemes, and retrofitting buildings.

As urban centers become more automated and data-driven, digital twins will be crucial to meeting decarbonization goals and designing green buildings. For example, a digital twin can take real-time environmental data and simulate those conditions in combination with various tactics, such as integrating renewable energy sources into a building. These highly precise simulations enable urban planners to see what works and what doesn’t in their city and draw up the optimal roadmap.

District heating systems are effective for making a city more environmentally friendly because they come equipped with advanced pollution control features and can be combined with renewable energy sources. For customers, district heating negates the need for boilers and fuel storage, improves air quality in their residences, and requires minimal maintenance.

Most buildings in the world simply are not sustainable, meaning they lack efficient water circulation, green rooftops, smart lighting, etc. However, demolishing a building to start anew brings its own detrimental effects to the environment. Retrofitting existing buildings is the best move that can be made when planning for a sustainable future. This paves the way for decarbonization efforts in our cities while avoiding building demolition.

Predictive maintenance is often used in warehouse, manufacturing, and industrial settings, as it allows operators to see when equipment is failing or how product demand fluctuates. This technology can be applied to smart cities to make sure that services like energy, water, waste management, and sewage are at peak efficiency and resources aren’t being squandered.

Go Beyond EVs for Sustainable Transportation  

Transportation is one of the biggest culprits of carbon emissions. For example, transportation accounts for 27% of all U.S. GHG emissions, according to the United States Environmental Protection Agency (EPA). One way sustainable cities cut down on the greenhouse gas emissions stemming from transportation is by buying into the promise of EVs. However, prices need to come down and citizens need an incentive for purchasing an EV. While EV adoption is the most obvious way to make city transportation more sustainable, there are a handful of other methods:

  • Encourage people to use e-bikes, e-scooters, and other green modes of transportation.
  • Encourage more people to take public transportation instead of driving their own vehicles.
  • Offer “smart parking” apps that let users locate empty parking spaces and reduce the time spent running a vehicle while looking for a space (this technology is in the pipeline).
  • Create zero- or low-emission zones where diesel-fueled vehicles are prohibited from entering or are forced to pay a fee. The idea is to encourage EV adoption in the city.
  • Deploy traffic management technologies that enable dynamic light signals. This reduces the time people spend sitting idly in their vehicles.

City governments should also invest in sustainable transportation systems. That means migrating to electric buses and electric taxi fleets. As you'll read in a bit, some of the greenest cities in the world have electrified their public transportation.

Modernize Waste Removal Practices 

It goes without saying that less waste is a great thing for the environment. On average, landfills consist of 50% Carbon Dioxide (CO2) and 50% methane. Smart bins are equipped with sensors that can detect when a bin or a dumpster is full and then notifies city services. As a result, this prevents waste overflow, which further pollutes a city. QR codes can also be used for this purpose, allowing passersby on the street to simply scan the smart bin to notify city services that it’s time for the bin to be emptied. Smart bins can also have a compactor installed inside them, allowing for significantly more rubbish capacity and ultimately, less frequency of removal services.

The analytics tracking that smart bins provide helps city officials decide where to prioritize waste removal. It enables city officials to tell where bins are, where they don't need as many of them, and where they need more of them. Sensors can even detect anomalies, such as cigarette butt droppings or a really foul smell stemming from a bin, prompting city officials to make an unscheduled pickup that benefits city dwellers.

Using Artificial Intelligence (AI), smart bins can also distinguish between normal trash and recyclables. The AI looks at the object dropped in the bin and decides which section of the bin to move the object to by cross-referencing it with an image database. This ensures that recyclables end up in a circular economy—a pillar for a sustainable city.

Some cities with green goals have invested in digitalizing their waste removal processes to make them highly efficient. With a more digitalized approach, trash pick-up routes can be modified to minimize mileage traveled. Moreover, this digitalized approach cuts back on unnecessary pickups and prevents the overfill of bins.

To get a better idea of how decarbonization tactics are used in urban areas, let’s take a look at seven examples of sustainable cities around the world.

Example #1 of a Green City: Ithaca, New York

In 2020, the Ithaca, New York town board unanimously voted to adopt a Green New Deal with the main goal of becoming carbon-neutral by 2030. By 2025, the town aims to deliver 100% renewable electricity to its residents and reduce the emissions from the town fleet of vehicles by 50%. Some of the accomplishments Ithaca has made include replacing its existing streetlights with LED technology, developing a residential energy score to improve the energy efficiency of existing homes, and installing an EV charging station at the town hall. Additionally, there’s a Tesla Supercharger station located at the local Trader Joe’s.

Figure 1: Photo of the Tesla Supercharger Station in Ithaca, NY (Source: PlugShare)

Photo of the Tesla Supercharger Station in Ithaca, NY


Example #2 of a Green City: Los Angeles, California

Los Angeles (LA) has very lofty goals, targeting carbon neutrality by 2035. Fortunately for LA, it has the benefit of a state-owned utility to manage energy sources that power the grid. LA has been ranked as the #1 Solar City in America 6 out of 7 years and has enough solar power for more than 140,000 homes. The city also has more EVs and charging stations than any other U.S. city, has piloted a recycled plastic asphalt process, and applies the Singapore Index to promote city biodiversity.

Figure 2: Solar Panels Installed on Roofs in Los Angeles (Source: Green Matters)

Solar Panels Installed on Roofs in Los Angeles


Example #3 of a Green City: Bristol, United Kingdom

Bristol is considered one of the greenest cities in the United Kingdom and has had a major influence on United Nations (UN) climate change initiatives over the years. In a 2022 study from clothes2order, Bristol received a sustainability score of 6.15 out of 10, which ranked seventh among cities in the United Kingdom. It was reported that the city had the following:

  • 928 renewable energy sites
  • 65.5 average university sustainability rating
  • 47.1% recycling rate
  • 28.5 charging stations per 100,000 people

Bristol needs to focus on creating more bodies of water and reserving a greater amount of space for the natural environment.

Figure 3: Graph of the Requirements to Meet Bristol’s 2030 Net-Zero Goals (Source: Center for Sustainable Energy)

Graph of the Requirements to Meet Bristol’s 2030 Net-Zero Goals


Example #4 of a Green City: London, England

London is known as a sustainable city largely in part due to its Ultra Low Emission Zone (ULEZ), which requires drivers to pay a fee if they don’t meet the emission targets. This process is carried out using technologies like Siemens’ Automatic Number Plate Reader (ANPR). If someone wants to avoid paying the fee, they either have to resort to public transportation or upgrade to vehicles that don't contribute to greenhouse gas emissions. The ULEZ expanded its domain by 18X in October 2021, which covers 380 Square Kilometers (km2) and 3.8 million people.

Users of Lime in the city of London can rent e-scooters and e-bikes through the Uber app as a more sustainable way to get where they’re going. The brand awareness and easy functionality of the Uber app will help increase the adoption of alternative transportation methods.

London also has thousands of parks and green spaces scattered throughout the metropolis, which helps combat air pollution in the sprawling city. The mayor’s office spends a great deal of focus on raising funds for developing new green spaces. Some recent projects include the Rewild London Fund, the Green and Resilient Spaces Fund, and the Greener City Fund.

Figure 4: Map of London’s Expanded ULEZ (Source: Carow)

Map of London’s Expanded ULEZ


Example #5 of a Green City: Barcelona, Spain

Barcelona tackles sustainability by providing incentives to its citizens. The advantages of owning an EV in the Spanish city are listed below:

  • 75% rebate on the tax associated with mechanically-powered vehicles
  • Exemption from a vehicle registration fee
  • Toll booth discounts when scrapping 10+-year-old vehicles
  • Free parking in select areas of the city

Barcelona city officials have partnered with Enel X and TMB to install ultra-fast charging stations for its public bus transportation system. In 5 to 8 minutes, the e-bus receives a 40% to 80% recharge. Like London, Barcelona has set up a Low Emission Zone (LEZ) to push more people toward electric cars, scooters, and other sustainable transportation. The LEZ consists of the municipalities of Sant Adrià del Besòs, L'Hospitalet de Llobregat, Esplugues de Llobregat, and Cornellà de Llobregat. The city also offers a free “Green Ticket” called T-Verda, which allows residents to scrap their diesel-fueled vehicles and receive free public transportation for 3 years.

Figure 5: E-Bus Traveling through the Streets of Barcelona (Source: Transports Metropolitans de Barcelona)

 E-Bus Traveling through the Streets of Barcelona


Example #6 of a Green City: Shenzhen, China

Shenzhen, a city located on China’s southeastern coast, has been crucial in developing the country’s manufacturing output, but that has come with significant environmental consequences. In 2010, the Chinese government chose the city of 13 million people as one of 11 provinces and cities to test decarbonization solutions. The city has come a long way and now has more than 16,000 electric buses and 22,000 electric taxis. Electrifying the fleet of taxis has resulted in about 70% energy savings and reduced annual emissions by 856,000 tons/year.

Shenzhen is the first Chinese city to use carbon trading and to issue carbo bonds, which incentivize enterprises to decarbonize. Some other notable actions this sustainable city has taken include pollution liability insurance, green infrastructure standards, retrofitting, park protection, and a ban on burning highly-pollutant fuels.

Figure 6: Photo of Shenzhen’s Electric Taxi Fleet Being Charged (Source: Phys.org)

Photo of Shenzhen’s Electric Taxi Fleet Being Charged


Example #7 of a Green City: Bratislava, Slovakia

Bratislava, the capital of Slovakia, has invested substantially in promoting a circular economy, and digitalizing its waste management processes is an integral component of this ambition. Smart waste management company Sensoneo is the main solution provider that the city has turned to. It has digitalized 85,000 containers, installed 1,753 Sensoneo sensors to track glass waste and underground bins, and deployed 92 Sensoneo WatchDog devices on waste removal vehicles, among other actions. This approach provides the city fuller transparency on the waste removal needs of the city and empowers waste removal operators to make timely pickup schedules. The city also leverages a fleet management platform to receive real-time updates about the routes and locations of the trucks on the road.

As part of its goal for zero-carbon building renovation, Bratislava has teamed up with the international European Union (EU) project GUGLE -Smart Cities and Communities. Energy efficiency is the cornerstone of Bratislava’s climate policy. Some ways the city addresses energy efficiency include enhancing the thermal capability of buildings (insulation, rooftop renovation, windows, etc.), using more efficient heating devices in flats, and using renewable energy sources like heat pumps, solar, and biomass systems. City officials have also schemed ways to position gas heating stations in locations where the distance for transition is relatively low in all directions, which saves costs.

With transportation accounting for a third of Slovakia’s pollution, Bratislava city officials have worked on a €246 million project that upgrades the city’s existing train and trolley systems. To make the city population act more sustainable, city officials are focused on educating citizens on the benefits of taking public transportation, so that fewer diesel-fueled vehicles pollute the local environment. In another project, Bratislava collaborated with oil refining company Slovnaft to install 90 bike-sharing stations with 750 bikes. Between late 2018 and mid- 2019, the following results were achieved:

  • 44,600 users
  • 275,000 journeys served
  • More than 500,000 Kilometers (km) traveled
  • Roughly 60,000 Kilograms (kg) of CO2 emissions saved

Figure 7: Photo of a Bike Sharing Station and Several Bikes Available for Rental in Bratislava (Source: welcometobratislava.eu)

Photo of a Bike Sharing Station and Several Bikes Available for Rental in Bratislava


Working Together to Make Our Cities More Sustainable

By and large, Europe has led the way when it comes to sustainability; however, the rest of the world has been catching up, mostly in North America, Asia, and Australia. But at the same time, countries in Arica, the Middle East, and Latin America still have a way to go, as their governments lack the financing and technology to create truly green cities. While technology is an absolute must-have for a sustainable city, the formation of alliances with other municipalities and nonprofit organizations is another key step to decarbonization. As governments continue addressing climate change via legislation and policy, urban planners can take tips from the sustainable case studies that are publicly available, such as those in this post, to plan for the long journey ahead.

To learn more about how sustainability is being pushed forward in modern cities and which technologies are support the process, download ABI Research’s Urban Decarbonization Strategies and the Role of Smart Cities research analysis report.