This page provides an overview of street sweeping and a discussion of water quality benefits and co-benefits of street sweeping.

Street sweeping overview

Graphic of street sweeping benefits
Benefits of street sweeping

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 (air) also poses significant air-quality concerns when entrained in the air due to wind.

Water quality benefits of street sweeping

graph of P removal with street sweeping
Research conducted by Bill Selbig (USGS) shows that streets, when cleaned of leaf litter prior to a storm, can significantly decrease phosphorus loads in stormwater runoff (Link to study)

Roadways accumulate debris and material such as sediment, vegetation, vehicle debris/waste, industrial emission particle deposition, and litter. Harmful pollutants which accumulate on roadways, parking lots, and pavement include metals, organics, nutrients, and particulate matter, which street sweeping helps remove. The effectiveness of street sweeping for removing specific pollutants depends on the timing and methods of sweeping, including season, frequency of sweeping, timing relative to runoff events, type of sweeper(s), sweeping practices such as speed of sweeper and vehicle parking, and the characteristics of the surface being swept (land use, surface roughness, etc.). Recommended sweeping practices for water quality purposes can be found on the page called Recommended street sweeping practices for water quality purposes. Links to other information on street sweeping, including case studies and credit calculations and calculators can be found on the page called Street sweeping.

Below is a qualitative summary focused on pollutant and sweeper type.

  • Nutrients (phosphorus and nitrogen): In areas with annual leaf drop from trees, nutrient removal is greatest at the time of leaf drop. Some additional benefit occurs with spring sweeping during seed drop. Sweeping at other times of the year provides limited benefit. However, in areas where fall sweeping is limited, early spring sweeping can remove material that contributes to nutrient loading. For more information on phosphorus, see Event mean concentrations of total and dissolved phosphorus in stormwater runoff.
  • Sediment and metals: Sediment removal as discussed here does not include coarse organic sediments, which would be included in the discussion for nutrients. Removal of metals is strongly correlated with sediment removal for most metals. In areas where sweeping cannot be done during winter, sediment removal is greatest immediately following snowmelt, or during snowmelt if streets can be accessed. Sediment buildup increases with length of time between runoff events. Sediment and metal concentrations are typically greatest in industrial and major transportation areas. Sediment associated with first flush is a greater concern in small watersheds with highly connected impervious surfaces. Focused sweeping should occur in areas where there is a significant amount of construction activity. For more information on sediment see Event mean concentrations of total suspended solids in stormwater runoff.
  • Chloride: Chloride is a concern in areas where road salt is applied as a deicer. Sweeping in late winter and early spring can remove residual road salt from impervious surfaces and decrease chloride loads in those areas. However, since chloride is a mobile pollutant, disposal of these sweepings may create concerns in other areas.
  • Bacteria and pathogens: There is limited information on the effectiveness of street sweeping for bacteria and pathogens, though we have a better understanding of factors affecting bacteria loads in runoff. Bacteria concentrations in stormwater runoff are typically greatest in warmer months and in residential areas. Street gutters and grit chambers may be important sources of E. coli contamination due to presence of moist conditions and an organic substrate. Limited studies indicate street sweeping is about 50 to 75% percent as effective for removing bacteria compared to sediment. Dry vacuum sweepers appear to be more effective at removing bacteria compared to other sweepers.
  • Sweeper type: Generally, the effectiveness of sweepers is High efficiency > Regenerative air > Vacuum > Mechanical broom. However, effectiveness varies with a variety of factors, including type of material being collected, targeted pollutant, characteristics of the impervious surface (e.g. roughness), operation factors (e.g. speed), supplemental technology (e.g. use of LIDAR), and whether sweepers are used in tandem (e.g. brush and vacuum). For example, brush sweepers may be more effective than regnerative air sweepers at removing coarse sediment (Tobin and Brinkman, 2002). For more information see Key functionality, limitations, and examples of street sweeping equipment and Different Types of Street Sweeping Technology.

For more information on stormwater and pollutants in stormwater, link here.

Co-benefits of street sweeping

photo leaves blocking storm inlet
Storm drain inlet partially blocked by leaves, increasing the potential for street flooding.

Street sweeping provides several benefits in addition to water quality improvement. The most cited co-benefits include improved appearances (aesthetics), improved roadway safety, potential reduction in flooding associated with clogging of stormwater conveyance systems, and reduced air pollution. Many key benefits associated with street sweeping have cumulative impacts as well. For example, increased removal of fine particulate matter can reduce the sediment load to downstream BMPs, extending the life of these practices which provide improved water quality further downstream.

  • Aesthetics: Sweeping removes debris from streets.
  • Safety: The removal of roadside debris lessens the rate of vehicle accidents and improves driver, biker, and pedestrian safety.
  • Pavement protection: Establishing a routine sweeping schedule in your community will help remove wearing debris and extend the life paved roads and paths.
  • Environmental: Street sweeping helps eliminate the number of plastics and litter that end up on the sides of roads and ends up harming local wildlife.
  • Air quality: Street sweeping removes particles and associated pollutants, including toxics, that could otherwise be transported in air. Regenerative air street sweepers appear to provide the most benefit with regard to collection of small particles and prevention of re-entrainment. The greatest effect of sweeping is on larger particles (e.g. PM10 vs. PM2.5).
  • Flooding: Removal of debris reduces the likelihood of blocking stormwater conveyances, thus reducing the likelihood of street flooding.
  • Effects on downstream best management practices: Sweeping is a form of source control or pretreatment, which decreases loading to downstream bmps, extending the life of and decreasing the need for maintenance of those bmps.

An indirect effect of enhanced street sweeping is incentivizing expansion of urban forestry, which has numerous benefits. See Green Infrastructure benefits of tree trenches and tree boxes.

References

Additional links

This page was last edited on 11 August 2022, at 14:29.