Sustainatry

Inspiration

Jane Street's brief said it plainly: most of the team drives to the office. We didn't want another app that nags people onto the bus. We wanted one that shows the honest number for every way of getting in, pays points for the cleaner choice, and admits that some days the car is the sensible option, so on those days it finds you someone to share it with.

What it does

Commute takes any start and finish, from your home, the office, a saved place or a typed postcode, and lays the options side by side: drive, bus and tube, cycle, walk, and a shared car with a named colleague. Every row carries its CO2 per trip from the UK Government conversion factors, the cost, the time, and the XP a logged trip pays. XP is the share of your own solo drive you avoided, so a two mile cyclist and a twenty mile cyclist both earn 100, and the leaderboard compares choices, not distances. Weekly prizes go to the top three and milestones are kept for good.

Shared rides are the part we're proudest of. The app matches people whose drives overlap, routes the real detour, splits the saving between the two seats, and only pays the sharing bonus when sharing actually saves something. Once both accept, they see each other's number.

How we built it

Next.js and React on the front, with a MapLibre globe that swoops from orbit to your street and draws each route as a line. FastAPI and Postgres on the back. Five public data sources, none needing a key: postcodes.io, OSRM for car, cycle and walking routes, the TfL Journey Planner for bus and tube, Open-Meteo for the weather nudge, and the gov.uk factors with HMRC fuel rates pinned in code. There is no AI anywhere in the feature; every figure is deterministic and traceable.

Challenges

The public OSRM server returns a driving time for its cycling and walking profiles, so we recompute those at 15 and 5 km/h and label them as estimates rather than pretending. TfL's distance field on tube legs is nonsense, so we measure legs along their own line string. Our first XP rule paid kilograms saved, which meant a long commute won by default; switching to a percentage of your own baseline fixed that and immediately exposed the next exploit, farming points with dozens of 10 metre walks, so trips under a kilometre and more than four a day stopped scoring. Carpool maths had a subtler bug: the detour changed depending on who was looking, so we fixed the requester as the driver and measure once.

What we learned

Every honest number needs a label for when it isn't one. The arrival check deters but doesn't prove, and saying so on screen earned more trust in testing than hiding it would have. And the sharing bonus has to be zero when sharing saves nothing, or the leaderboard rewards the wrong thing.

What's next

Expected routes and times on each profile, so frequent commuters on your route get notified when you look for a ride, and a GPS trace to make the arrival check real.

Built With

• fastapi
• maplibre
• next.js
• python