Leaf: Transport Emissions Cut By Behaviour
UX Design, Mobile
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© 2019
Nanda Dias Design
© 2026
Nanda Dias Design
A three-day sprint against six teams, tasked with cutting transport CO2e by 20% in 2 years. We won on behaviour change, not new technology, and the jury even asked to buy it.
A three-day sprint against six teams, tasked with cutting transport CO2e by 20% in 2 years. We won on behaviour change, not new technology, and the jury even asked to buy it.
As the elected Decider on a three-day international sprint, I narrowed six teams' worth of competing ideas down to one behaviour-change concept. It beat every rival team and the judging panel asked to buy it outright.
My 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 a behaviour problem, not a technology one.
The sprint's facilitator put me forward 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. Five people, most of us meeting for the first time that morning: a UI/interaction designer, a visual designer, two from sales, one full-stack developer. My scope ran end to end, problem statement, persona, concept direction, prototyping, and the pitch itself, all while keeping five strangers moving toward one decision with a clock running.
What I Did
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, not technical novelty, 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.
Key Challenges & How I Addressed Them
Challenge: We had no real cost model for building the app, and no time to get one. The instinct is to hide that gap or spend precious hours chasing it.
Solution: We named the gap to the jury rather than papering over it, and used behaviour, not feasibility, as the filter for every decision instead. The trade a Decider actually has to make isn't which idea is safest to defend, it's which idea is honest about what we don't know yet.
Challenge: Five people, five backgrounds, most of us had never worked together before, and getting to one direction fast meant real disagreement had to get resolved in minutes, not days.
Solution: I made the calls plainly and explained the reasoning out loud each time, so the team could disagree with me and still trust the process even when they didn't get their way.
Challenge: Looking back, the thing I'd flag isn't a design decision, it's a validation one. We tested the reward mechanic with 5 users who matched our persona, in a single round, with no time for a second. That is real signal for a direction, not proof it holds up at scale or outside that persona.
Solution: I said exactly that to the jury instead of overselling the concept as more tested than it was. Naming the limit was part of the pitch, not a weakness in it, and it's why I still wouldn't claim more from this project today than a strong, judge-validated direction.
My 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 a behaviour problem, not a technology one.
The sprint's facilitator put me forward 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. Five people, most of us meeting for the first time that morning: a UI/interaction designer, a visual designer, two from sales, one full-stack developer. My scope ran end to end, problem statement, persona, concept direction, prototyping, and the pitch itself, all while keeping five strangers moving toward one decision with a clock running.
What I Did
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, not technical novelty, 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.
Key Challenges & How I Addressed Them
Challenge: We had no real cost model for building the app, and no time to get one. The instinct is to hide that gap or spend precious hours chasing it.
Solution: We named the gap to the jury rather than papering over it, and used behaviour, not feasibility, as the filter for every decision instead. The trade a Decider actually has to make isn't which idea is safest to defend, it's which idea is honest about what we don't know yet.
Challenge: Five people, five backgrounds, most of us had never worked together before, and getting to one direction fast meant real disagreement had to get resolved in minutes, not days.
Solution: I made the calls plainly and explained the reasoning out loud each time, so the team could disagree with me and still trust the process even when they didn't get their way.
Challenge: Looking back, the thing I'd flag isn't a design decision, it's a validation one. We tested the reward mechanic with 5 users who matched our persona, in a single round, with no time for a second. That is real signal for a direction, not proof it holds up at scale or outside that persona.
Solution: I said exactly that to the jury instead of overselling the concept as more tested than it was. Naming the limit was part of the pitch, not a weakness in it, and it's why I still wouldn't claim more from this project today than a strong, judge-validated direction.
Design Iterations, and What Won
Ideation: one candidate solution per persona pain point, so every idea had to answer to a real behaviour first, not to which technology was newest.
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, not an internal panel, judged 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.
Outcomes
Competing teams
6
Countries represented
6
(02)
© 2026
(02)
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(Frequently Asked Questions)
What does complex, large-enterprise B2B SaaS experience actually give me, and would I still move fast enough for a smaller team?
How do I work when the brief isn't clear yet, and what part of the job do I enjoy most?
How do I actually strengthen a team, and will I get hands-on or mostly direct from a distance?
What did I do with the time between roles, and where do I actually stand on AI in my day-to-day work?
How has living abroad shaped me, and am I looking for something long-term, or a bridge while I sort out next steps?
(03)
(Frequently Asked Questions)
What does complex, large-enterprise B2B SaaS experience actually give me, and would I still move fast enough for a smaller team?
How do I work when the brief isn't clear yet, and what part of the job do I enjoy most?
How do I actually strengthen a team, and will I get hands-on or mostly direct from a distance?
What did I do with the time between roles, and where do I actually stand on AI in my day-to-day work?
How has living abroad shaped me, and am I looking for something long-term, or a bridge while I sort out next steps?
(03)
(Frequently Asked Questions)
What does complex, large-enterprise B2B SaaS experience actually give me, and would I still move fast enough for a smaller team?
How do I work when the brief isn't clear yet, and what part of the job do I enjoy most?
How do I actually strengthen a team, and will I get hands-on or mostly direct from a distance?
What did I do with the time between roles, and where do I actually stand on AI in my day-to-day work?
How has living abroad shaped me, and am I looking for something long-term, or a bridge while I sort out next steps?