Daily commutes in private cars are a major source of urban carbon emissions. Changing commuter behavior means untangling habit, cost, convenience, infrastructure and city planning all at once.

Create a scalable solution to reduce carbon emissions from daily commuting in a medium-sized city. Study who is affected, dig past the obvious symptoms to the real root causes, and design a solution that could actually work in the real world. There is no single correct answer — what matters is the quality of your thinking, the stakeholders you consider, and how clearly you justify your chosen direction.

• Who is most affected by this problem, and how did you account for them?
• What is the single biggest risk to your solution working?
• Which assumption, if wrong, would break your whole idea?