A guide to best practices for cleaner cities

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Urban cleanliness is an essential component for the attractiveness and safety of a city, and for the quality of life of its inhabitants. It also has a significant role to play in the city's sustainability. Street litter can end up in the natural environment. In addition, cleaning uses energy, water and emits noise, dust and CO2. Keeping a city clean is a challenge for modern cities, as population and mobility increase, behaviors change, and public budgets are under scrutiny.

The mission of municipal cleaning services is to ensure a clean city and to preserve the environment. Most municipal cleaning services manage their operations with weekly routine schedules. Some of them have introduced the measurement of cleanliness and the development of a continuous improvement process. What cannot be measured, cannot be improved.

In this report, we present how urban cleanliness, resources and environmental footprint can be optimised with a data-driven approach. We propose metrics and discuss best practices from exemplary cities and from dedicated field experiments conducted in Cortexia's "Clean City Lab" in Geneva. The findings and improvement measures from these experiments are summarised at the end of this report.

It is therefore intended to provide a guide of best practices, for which the impact has been objectively demonstrated in the field, and which can be used by municipalities or Producer Responsibility Organisations seeking to optimise public cleaning services. For further details, the reader is invited to read the publicly available "Clean City Lab" articles.

2. Metrics

A quality management approach has been developed to improve urban cleanliness, save resources and preserve the environment, for which we propose the following quantitative measurements:

Cleanliness level

Depending on the goal, urban cleanliness may be assessed with population surveys, litter monitoring (i.e. counting) or assessment of a cleanliness grade. Various methodologies have been defined at national level and implemented at municipal level. Litter monitoring and cleanliness grading are relevant respectively for:

• Environmental monitoring, for example to assess the impact of anti-littering campaigns or assess progress towards plastic litter reduction targets.
• Urban cleanliness management, for instance to measure the cleaning department's efficiency and quality of service. We use the "Clean City Index", a methodology developed by the city of Zurich in 2000. This index is representative of the users' cleanliness perception of a street on a scale from 0 (dirty) to 5 (clean). It is public, in use in Switzerland, Germany and Austria, and allows the identification of the type of soiling.

Resources (costs)

The most accurate way to evaluate the efficient use of resources for municipal cleaning services is to assess the cleaning costs. Municipal cleaning cost accounting would be the most accurate approach, but it can rarely be used because cities do not usually report on these cleaning costs separately. Alternatively, estimations based on people and machine hourly rates (bottom-up approach) can give good first estimates.

Between cities of the same country, per capita cleaning costs vary by a factor of one to four, without being correlated to the level of cleanliness. This means that using more resources does not necessarily lead to a cleaner city. We rather believe that efficiency gains are achievable by sharing best practices among cities and municipalities.

Environmental impact

We have identified and characterised three categories of environmental impacts: litter leakage to natural environments, use of water for cleaning, as well as CO2 emissions and air pollution from machinery:

• Public litter which is not collected may end up in the environment, mostly through waterways. This concerns mainly single-use plastic items, such as cigarette butts and plastic packaging of single-use products. Geneva's cleaning services estimated that between 1 and 2.5 cigarette butts are littered daily per capita. We measured that 18% may remain after sweeper cleaning. By placing filters in water drains on a street in Geneva, we have measured that approximately 2% of the cigarette butts present on the street will leak into the waterways.
• On the other hand, cleaning operations impact the environment. Some cities use street washing machines, which consume considerable amounts of water (predominantly drinking water). A direct consequence of this washing is that the water flushes litter down the drains to waterways. A city that cleans without washing will use 30 times less water per capita.
• Finally, street sweepers work mainly with diesel engines and emit yearly around 200 tonnes of CO2 per 100,000 inhabitants, along with other air pollutants.

3. Prevention: reduction of littering

Reducing littering — soiling less — is a sustainable approach to achieving a cleaner city by tackling the issue at its source. Adequate urban waste furniture and consumer-targeted communication play the key role.

Public trash bins allow people to dispose of their waste correctly. Whereas cities often focus on the quantity of bins to be placed, their effectiveness — the amount of litter found on the street after a given period — is even more important. This effectiveness is greatly dependent on the bins' appearance and position. Well-placed and visible bins, such as coloured or signposted bins, are more likely to be used. Working on behaviour through advertising and nudges is effective and may reduce littering by 25% to 50%.

Special attention should be paid to hotspots that attract litter, such as domestic waste collection points. Overflowing or dirty bins may cause users to become more negligent and litter more.

Increasing the effectiveness of public bins for cigarette butt disposal is particularly critical, as one study found that 75% of littering acts near public bins are carried out by smokers, many of whom are not comfortable using the bins. Ashtrays or stubbing plates should be easily recognisable. By changing the design of public trash bins, making the ashtray evident and improving cigarette butt collection, the city of Geneva halved the amount of litter around the bins.

The management of public bin and ashtray infrastructure is also subject to optimisation. The mean bin filling rate at Geneva's Clean City Lab is 40%. We estimate there is generally a potential to reduce the number of bins by 20% to 50% by adopting a sensible global approach considering bin design, size, functional efficiency, integration in the urban architecture, ergonomics, maintainability and improved signage.

Cigarette butts also get littered directly in stormwater drains and may thereby end up in waterways. Dedicated signage addressed to the public, for instance directly on the drain, can help to prevent such subsequent water pollution.

4. Remediation: improving cleaning efficiency

Cleaning vehicles are typically engaged on a routine schedule and will run regardless of how clean or how dirty the street is. Measuring the level of cleanliness allows cleaning to take place only when and where it is necessary, thereby increasing the efficiency of services.

In the Clean City Lab district, the Geneva Cleaning Services defined their target cleanliness level. The district is divided into areas cleaned according to a routine weekly schedule. An initial cleanliness measurement identified areas where cleanliness was above target and areas where it was below target. Cleaning in the areas above target was reduced in order to clean more frequently the dirty areas. The result was a higher and more uniform cleanliness, matching the target, across the entire district.

In a second step, the sweepers' routes were rearranged in each area according to the level of cleanliness and the time needed to clean the streets. This resulted in savings of one in three street sweepers and 20% of machine hours, while still ensuring the targeted cleanliness level was attained.

In the down-town district of the city of Utrecht (Netherlands), the cleanliness level was unevenly distributed across different areas. The municipal cleaning services adapted Geneva's approach by reorganising the size of the cleaning areas. The result was a more uniform and higher level of cleanliness to the satisfaction of shop owners and citizens. Four out of ten workers could be freed up for other tasks, such as littering prevention.

The city of Basel defined the necessary number of street sweepers to achieve the target level of cleanliness based on vehicle utilisation rates and cleanliness measurements. They reduced the total number of sweepers by 15%, which helped to offset the transition cost to more expensive electric vehicles. This is how Basel will fulfil its target of 95% zero-carbon cleaning by 2025.

These real case examples demonstrate a simple method to achieve a higher and more uniform level of cleanliness with fewer resources and lower CO2 emissions. Potential resource savings are in the range of 10% to 20%.

5. Toolbox

This guide proposes practical solutions to improve urban cleanliness and reduce littering. The solutions use cleaning and prevention resources in more efficient ways, making them attractive for municipal cleaning services. The most commonly found situations and their mitigations are shown in the table below.

6. Conclusion: solutions for sustainable improvement

There are many initiatives to address urban litter. There are fewer where effectiveness and efficiency have been measured quantitatively in an objective manner. Such best practices which have been proven effective, as the ones described in this paper, should be shared and replicated to reach economies of scale and improve their impact. Only a broad approach, borne by all stakeholders, will solve the issue.

This is why, in our opinion, it is of utmost importance to measure quantitatively and objectively the effectiveness and efficiency of each action. This effectiveness should be measured in terms of impact (reduction in the quantity of litter or improvement of the cleanliness index), costs and scalability.

Achieving environmental commitments for a company, or targets for cleaner and more sustainable cities, requires a structured and sustainable approach based on shared responsibility, stakeholder collaboration and data-driven measures.

This is especially true for cities. In Europe, cities account for 75% of the population. Urban littering has a significant impact on the environment. 300 billion cigarette butts are littered annually in Europe, 12 billion of which end up in the oceans. Cleaning uses resources and emits CO2.

The municipal public cleaning services have a central role to play. They need a structured approach, inspired by quality management frameworks for continuous improvement such as the Plan-Do-Check-Act cycle or the more recent operational excellence methodology, to focus on the most effective actions, improve them in a continuous loop and achieve a clean and sustainable environment.