Leaf: Transport Emissions Cut By Behaviour

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Nanda Dias

Product Strategic Design

Leaf: Transport Emissions Cut By Behaviour

UX Design, Mobile

Nanda Dias | Staff Designer

A three-day sprint to cut transport emissions. Our concept won, driven by behaviour change.

A competition among six teams from six countries, tasked with cutting transport CO2e by 20% in two years. Chosen as Decider, I kept the group focused on whether each idea would actually change behaviour, the question that led me to suggest gamification.

Role & Approach

Six teams from six countries had three days to answer one brief: cut CO2e emissions from urban mobility by 20% in two years, in a world where changing how people commute is fundamentally a behaviour problem.

The sprint's facilitator chose me as Decider, the design-sprint role that sets the criteria for a decision and breaks ties when the team can't agree, given my MSc research in smart cities and mobility, my own reading on behaviour-change design, and hands-on gamification experience from TobyRich. I already knew two of the team, a UI/interaction designer and a visual designer, from working together before; the other three, two from sales and one full-stack developer, were new to all of us that morning. My scope ran end to end: problem statement, persona, concept direction, prototyping, and the pitch itself, with a moderator keeping the sprint's structure and pace on track.

The brief sat inside the UN's Sustainable Development Goal on Climate Action, which gave the three days real external stakes rather than an internal hackathon exercise. Decider is closer to a company's CEO than a design title: someone has to own the call when the group can't agree in the time left. My own lens on it stayed narrow on purpose: how people actually move through public space, their commuting habits, and what would make a reward or social-appraisal system change behaviour rather than just decorate the app. Keeping that lens in front of the team is what led me to suggest gamification, drawing on my TobyRich experience incentivising behaviour change through social mechanics.

Decisions and Actions

Framed the problem statement and the persona first, so behaviour was the lens before anyone touched a screen. Ran the crazy-8s exercise to ideate a candidate solution for every persona pain point, then, as Decider, narrowed the field to the two or three strongest candidates using behaviour-change fit as the criterion. Prototyped on paper and tested with 5 users matching the persona, synthesising results fast enough to still redesign before the pitch. Shaped the pitch itself, wording and data, since a three-day sprint is won in the room as much as in the concept.

Role & Approach

Decisions and Actions

Key Challenges & How I Addressed Them

No cost model for the build: named the gap to the jury instead of hiding it, and used behaviour-change fit as the filter for every decision.

A newly formed team, one fast decision: made each call plainly and explained the reasoning out loud, every time, so the team could disagree with me and still trust the process.
One validation round, no time for a second: told the jury the result was a strong signal, with the at-scale question still open.

The trade a Decider actually has to make isn't which idea is safest to defend, it's which idea is honest about what the team doesn't know yet.

Design Iterations & Learnings

Ideation: one candidate solution per persona pain point, so every idea had to answer to a real behaviour before anything else.

Narrowing: as Decider, I cut the field to the two or three strongest candidates using behaviour-change fit as the criterion, then committed the team's remaining time to those only.

Final: Leaf, a rewards-based mobility app built on reward systems and social appraisal. External judges called it the most innovative and appealing concept in the room, and asked to buy the concept outright. We declined. A service with a strikingly similar reward mechanic, Jelbi, launched in Berlin not long after. I can't claim a direct line between the two, only the resemblance.