130,000 Reasons Why Data Science Can Help Clean Up San Francisco
By Aleksey Bilogur.
Every urbanite knows how important clean streets are to the attractiveness and viability of a neighborhood. Clean streets mean walkable streets, walkable streets mean busy streets, and busy streets mean prosperous neighborhoods.
Nobody knows this better than the founders of rubbish, Emin Israfil and Elena Guberman. Armed with trash bags and eye-catching smart litter grabbers, aka “rubbish beams”, they have picked up an impressive 130,000 individual of litter over a year of consistent street cleanings in San Francisco. All the while, the rubbishers collected data on what type of litter was picked up, where, and when.
This article is the first-ever analysis of this unique and expansive dataset. We will slice and dice the street pickups by location, type, and time — learning how our habits as pedestrians and residents of our communities affect our urban environment in the process.
Setting the scene
Rubbish runs are conducted on four blocks of Polk Street, between Filbert and Broadway, in the Russian Hill neighborhood of San Francisco. During each rubbish run the volunteer rubbishers aim to clean up every piece of litter that is on the ground, including litter clogging gutters and drains.
Polk Street is most residential at its northern end but becomes more commercial as you go further south. Commercial areas are more trash-laden than residential ones, due to increased foot traffic, and Polk Street is no exception. If we plot the average number of pieces of litter on the street per block per day, we see just how strong this effect is:
In just a couple of blocks, litter pieces of litter jump from just 16 items per day to an incredible 90 items per day. Put another way, the cleanest block on Polk Street is littered on 5,800 times per year; the dirtiest, 32,000 times per year.
The block of Polk Street between Broadway and Vallejo is more than twice as dirty as the block directly across the street (90 pickups per day on the west side, just 37 per day on the east side) even though both blocks are 100% commercial.
What’s causing this increase in litter? Litter correlates to both business location and type. Anecdotally, businesses that have more to go items plus foot traffic contribute more litter overall. The west side of Polk Street has all of the street’s pizza shops and bars, plus a nightclub, whilst the east side of Polk Street has pharmacies and hardware stores and a bookstore. And while the two sides share the neighborhood’s restaurants and coffee shops, the difference between a sidewalk abutting Rouge Nightclub and one abutting Walgreens is easy to see:
In this visualization, the west side of Polk Street is on the bottom, and the east side, on the top. Filbert Avenue, the northern edge of the pilot zone, is on the left end; Broadway, the southern edge, is on the right.
The data may also be broken down on a business-by-business basis, which highlights how much litter volumes change based on business location:
“Mean litter” is 36 pieces of litter per foot frontage per year. A typical storefront, 20 to 25 feet wide, will have an average of 800 individual pieces of litter picked up per year — that’s roughly three pieces of litter per day. Areas with higher foot traffic may have three times as much litter as areas with less.
What about litter types?
Now that we understand where litter ends up, a good follow-up question is what types of litter end up there.
Rubbish separates litter into five categories. The majority of street litter consists of two types: tobacco, primarily cigarette butts, and paper, e.g. napkins and receipts. Plastic items like chips bags are also common. A small percentage of rubbish is food or glass. Finally, there’s other for things that don’t fit anywhere else.
Here’s what we see if we plot litter picked up by type over time:
Litter picked up on Polk Street is 45% tobacco, 32% paper, 14% plastic, 1% food, 1% glass, and 7% other. Rubbish’s data on litter is reasonably consistent over time, but does occasionally deviate: April 22, 2019, is a prominent example, though we don’t know for sure what happened that day to cause it.
(You may be wondering about what the team does about when it encounters certain “special cases”. Rubbish reports discarded needles and 💩 to SF311, using a reporting tool built directly into the rubbish app. The team has on occasion recovered and returned a stolen thing or two to their original owners — but that’s a story for another time!)
What about litter over time?
The rubbishers love to talk about “the good neighbor effect”. Over the course of their time cleaning up Polk Street the Rubbish team has been approached and questioned by many of the local businesses and straphangers in the neighborhood (and, in typical San Francisco fashion, netted a few venture capitalists’ business cards in the process). Their visibility and approachability on the street have made locals more conscious about how actions and business policies affect the street they serve, work on, and live on.
Another equally important effect is the “clean streets” effect. The Rubbish team talks extensively about the fact that the cleaner the street, the less likely it is to be littered on. As pedestrians, we seem to psychologically reserve our littering tendencies for those streets which are already dirty. If there’s already litter on the street, will anyone even notice one more candy wrapper or receipt stub? The cleaner the street, the more slowly it accumulates new litter.
The volume of litter picked up on Polk Street has descended precipitously over time. And while it’s impossible to know for sure what caused it, it’s easy to see how the constant street presence and cleanup work done by the Rubbish team has had an impact:
“Peak litter” occurred in late 2018, after which there was a sharp decline going into the new year. The amount of litter dropped on Polk Street has been declining slowly ever since. On a typical day in November 2018, rubbishers might pick up 1000 pieces of litter dropped onto the street; by February 2019, just a few months later, 400 was more typical.
Many of the peaks in this dataset correspond to holidays and/or events that bring more people out onto the street — Halloween, for example, shows up prominently.
Polk Street was at its cleanest immediately following a community-organized street cleanup in late May. The dip in late November happened around the time of the Camp Fires, which reduced air quality in San Francisco to dangerously low levels, freezing street activity in the process. And the dip in early June corresponded with the SF heat wave, a week that saw temperatures in the Bay Area hit a stifling 100 degrees, making it unpleasant to be outside.
Conclusion
It’s exciting to see how much we can learn about street litter patterns by looking at litter pick up data. And, although we have access to a year’s worth of data, important trends begin to emerge after only a few days. Perhaps data like this can one day become part of a community organizer’s toolkit.
Rubbish is working with cities and communities to create a smart approach to litter, using data to put cigarette disposals and trash cans where they will have the biggest impact. Understanding litter trends and how they vary from street to street can tell us a lot about our communities and can be a powerful tool in helping identify the source of litter to clean more effectively. We look forward to seeing how technology can help our cities become healthier, safer and more sustainable.
