The challenge
Over half of single-family recycling was contaminated, driving up the city’s hauling costs.
The case
San José’s Environmental Services Department launched the Contamination and Recycling Tagging (CART) program in March 2024, after 57% of the single-family recycling stream was found to be contaminated in 2022. Paid city ambassadors lift cart lids on collection day and leave an ‘Oops’ or ‘Good Job’ tag, aiming to reach all 216,800 single-family homes. In 2025 the Bloomberg Cities Idea Exchange Evaluation Fund ran a trial with 5,457 households, assigned to treatment or control by odd or even street number. A single tag cut contamination by 6.7 percentage points, or 18.9%, one to two weeks later. ‘Good Job’ tags and ambassador conversations made little difference. Evaluators estimated $160,000 in savings for every $100,000 spent in the first 16 months.
Why it worked
Specific, personal feedback at the moment of the mistake changed sorting, while praise and conversations did not. The effect was measured only one to two weeks after one tag, and earlier studies suggest repeated tagging works better, so long-run savings are an estimate.
Sources
- Bloomberg Cities Idea Exchange (2025). Evaluation report for San José’s recycling feedback program. Bloomberg Philanthropies.
- Bloomberg Cities Idea Exchange. Recycling contamination. Bloomberg Philanthropies.
- City of San José. Single-family recycling cart tagging program. Environmental Services Department.
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