Recommended street sweeping practices for water quality purposes

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This guidance document is intended to instruct the user on best practices associated with street sweeping and provide the user with key information and resources to successfully develop and execute a street sweeping program. This guidance was developed in partnership with MPCA for eventual incorporation into the Minnesota Stormwater Manual.

Topics covered within guidance include the following, which represent subsections herein:

1. Street Sweeping Overview
2. Street Sweeping Equipment
3. Benefits of Street Sweeping
4. Effectiveness of Street Sweeping (locations, timing, frequency)
5. Managing Street Sweeping Waste
6. Cost Considerations
7. Training for Street Sweeping Professionals
8. Street Sweeping Program Development
9. References

There is a wide breadth of data, research, and resources available related to street sweeping, this guidance is intended to aid in the understanding of street sweeping, its benefits, and links to a variety of helpful resources for a municipality seeking to review or develop its own street sweeping program. Note that the most common street sweeping practices, equipment, and technologies vary by location, but the focus of this document is on the United States, with specific relevance to the State of Minnesota to the extent possible.

Street sweeping overview

Street sweeping (also called street cleaning) refers to removal of sediment, litter, or other accumulated substances on roadways, particularly in urban and suburban areas. Street sweeping does not include removal of large quantities of leaves brought to the street/verge for removal, large debris or bulky items; removal of these items is typically handled by large vacuum leaf collectors or dump trucks, respectively.

Historically, street sweeping was conducted manually by a sanitation worker with a broom or shovel to remove animal waste from horse-drawn vehicles and other detritus on roadways. Mechanical sweepers such as broom systems attached to horse carts came about in the mid-1800s, and in the early 1900s street cleaning wagons sprayed water onto roadways to wash away debris. Motor-driven street sweeping vehicles were patented in the US in 1917.

Modern street sweeping has improved efficiency of debris removal from roadways dramatically. The focus of street sweeping was simple large “cosmetic” debris removal until the 1970s when concerns about water quality arose. In the decades following, improvements in street sweeping technology focused more on the removal and collection of coarse sand particle-sized street dirt, and smaller particles which contribute to instream sediment and nutrient pollution when swept off of or washed into waterways. Even when a street was cleaned of large refuse, the amount of tiny particulate matter that could not be effectively removed manually remained to wash-off into waterways following precipitation. Pollutants in stormwater runoff have long been recognized as contributors to aquatic habitat degradation, nuisance algal growth, low dissolved oxygen and toxicity in receiving water bodies . More recently, there has been a focus on street sweeping to remove the organic matter produced by street trees (leaves, seeds, flowers, etc), which can contribute significant amounts of phosphorus to runoff, especially in the fall during leaf drop . Particulate matter also poses significant air-quality concerns when entrained in the air due to wind.

Street sweeping equipment

The focus of this guidance is on modern mechanized advanced street sweeping technologies. These types of mechanized street sweepers for roadways fall into four categories.

• Mechanical Broom: Rotating cylindrical brooms flick dirt and debris onto a conveyor moving into a hopper for collection. These perform well in picking up heavy material like coarse sand, gravel, and trash, but are less effective in picking up fine particles. These sweepers are abrasive which can lead to the breakdown of larger particles into smaller particles, and they are less effective at penetrating cracks and potholes in pavement. Sometimes these sweepers have onboard water spraying systems to help control dust, although sometimes a separate flush truck is used in tandem with mechanical sweepers.
• Vacuum: An engine-powered fan creates suction to remove dirt and debris up into a hopper. A windrow broom directs detritus into the path of the vacuum nozzle. While the vacuum is better at picking up fine material than mechanical broom sweepers, there are still some difficulty in penetrating cracks and potholes with the windrow broom. Vacuum exhaust can emit dust into the atmosphere.
• Regenerative Air: An engine-powered blower pushes a blast of air across the width of the sweeper truck which penetrates cracks and potholes, then similar to a vacuum sweeper, debris is sucked into a hopper. A windrow broom directs detritus into the path of the air blaster and vacuum. To avoid dust emission problems associated with vacuum sweepers, regenerative air sweepers employ a closed loop cycle of blast air and suction air.
• High-Efficiency / New Technology: These trucks represent new technology that includes a combination of technologies from other sweeper types, incorporating both mechanical and vacuum aspects. New technology includes both electric/hybrid sweepers, as well as high-powered electric, autonomous street sweeper vehicles. Vehicles are smaller in size than traditional street sweeping trucks and use LiDAR-based machine vision technology to operate under all weather conditions.

Effectiveness and costs associated with different mechanized street sweeper types varies and are summarized in other sections of this guidance.

When selecting the type of street sweeper that is best for a given municipality, the factors to consider are listed below and discussed in the adjacent table.

1. Understanding where and how frequently sweeping will occur (e.g. urban roadways, parking lots, permeable pavement; quarterly, monthly, seasonally).
2. Characterizing the type of sweeping waste most prevalent (e.g. loose or compacted materials, fine or coarse sediment, level of trash debris)
3. Taking stock of whether it makes sense to conduct street sweeping in-house with trained municipal staff or contract the work to a private street sweeping company.
4. Consider the cost, user-friendliness, and efficiency ratings of equipment.

Key functionality, limitations, and examples of street sweeping equipment