Chennai drives alone. The calculator goes global.
When I built and launched the Chennai Traffic Impact Calculator, I was already planning to make it global. But I wanted a good PoC first. And I wanted to know how much I could rely on organic distribution. So beyond the initial push, I purposefully left it to run on organic growth.
On a normal day, the calculations stayed in single digits. But the search interest spiked around long holidays and festivals. It makes sense: that’s when a huge chunk of Chennai empties out to hometowns, the outer-city roads choke up, and people start Googling their way to the traffic. And, in that process they also searched about their regular commute.
Now we have ~2,000 calculations across eleven months, and I’ve seen enough patterns to push things further, and that’s how the Commute Impact Calculator was born. It replaces the Chennai Traffic Impact Calculator, and now includes Bengaluru and Metro Manila.
But before diving into the new tool, I want to tell you what we’ve learnt about Chennai from the old one. I think we have a good enough sample to draw some real insights from.
Here are the top five insights about the city’s transport landscape and its impact on residents.
1. The disproportionate carbon footprint of cars
While cars are only 41.3% of the commutes measured, they’re responsible for a staggering 69% of the total carbon emissions. The driver of that inefficiency is solo driving: 27% of all commutes recorded were a single person alone in a five-seat car, and 65% of all car trips were solo. Shifting just those solo trips to public transport would erase about 80% of their emissions. That’s roughly 300 tonnes of CO₂ a year, in this small sample alone.
But what to say… I’m convinced that people who choose the car for their commute will keep choosing it even when they have good public transit options. Utility vehicles now make up roughly 65% of new passenger vehicles sold in India, and within the tool’s sample, 26% of car commutes were already SUVs, despite emitting 19% more carbon than a hatchback for the same trip.
Many Chennai commuters are picking larger, more impactful vehicles even when a smaller, more efficient one would do for the distance.
Only 7.8% of daily commuters even bothered to model an “off-peak” shift to dodge traffic. And even in this sample (people concerned enough to measure their commute), just 3.7% chose the Metro, while 41.3% chose a car. In this light, the car isn’t just a way to move; it’s a walled-off little world that lets the commuter opt out of the “mass” experience of the city. Even though only mass transit bends the curve on emissions and congestion, that unconscious preference for the private car stays the hardest barrier for any policy, Metro Phase 2 included.
2. The “self-selection” profile: the burdened commuter
The people who chose to measure their impact are the city’s hardest cases: commuters for whom travel is a genuine daily burden. Compared to official city averages, these tool users:
Travel nearly twice as far (14.1 km median vs. the city’s 8.5 km).
Lean much harder on private vehicles (75.6% vs. the city’s 60%).
Are less likely to use public transport (16.6% vs. the city’s 32.7%).
3. The “eight-day ransom” and financial cost
The median commute in Chennai takes 188 hours a year. That’s the equivalent of eight full days spent getting to work and back. The burden is financial too: a car commute costs roughly ₹26,340 a year, about 7% of an average Tamil Nadu resident’s income. Switching to a bus for the same distance would save a commuter around ₹13,000 a year.
4. Critical infrastructure gaps in “residence” communities
The data reveals a clear geographical mismatch: the OMR/Taramani IT belt and Guindy act as massive “job magnets,” pulling in workers from the South and West. Metro Phase 2 will eventually reach some of these areas, but several of the neighbourhoods that send the most commuters (Medavakkam, the Tambaram belt, and Ambattur) still lack direct rail and must rely on aging suburban rail or overcrowded buses
5. The two-wheeler carbon paradox
Despite their reputation, scooters and motorcycles are not a “green” solution for the climate. For an identical 12-18 km trip, a petrol two-wheeler emits 36 kg of CO₂ a month, more than double the 14 kg from a shared bus seat. Two-wheelers may ease road congestion compared to cars, but only mass transit truly “bends the curve” for both emissions and space efficiency.
(Detailed analysis stories on the way.)
A mistake I made early on with the calculator was adding pre-filled routes to reduce friction. Almost 25% of all calculations came from those routes, so they’re excluded from this analysis.
Once I started seeing the patterns, I started thinking about next steps. The calculator is, by design, open-ended: it tells you your commute score, but it can’t “solve” your commute’s impact. We kicked around ideas, and a good friend suggested offsetting the high scores through tree adoptions. A vendor was almost finalised, and then my self-contradictions kicked in. You can offset your emissions, but really you’re offsetting the guilt of a high score. The behaviour doesn’t change. And for a good reason: your choice of commute is an individual act. Beyond a point it’s your private, personal decision, fully backed by law and policy. But the impact of that decision is collective. That’s the nuance I wanted to explore first.
So I deprioritised offsetting and chose to start with social context instead. The Commute Impact Calculator builds on that: each city gets a set of chosen corridors, and as the data builds up for each corridor, it unlocks more for us to do. And once Bengaluru was in the picture, I decided to add at least one global city too. I wanted to see how far it would push the way I work on this project. That’s how Metro Manila, one of the most congested cities on the planet and choked with cars, joined the tool.
Lots more cool stuff is on the backlog. 11 AI agents are working hard on the next iteration of the Commute Impact Calculator. I’ll publish more insights from the Chennai data in the coming days, and I’ll try to write more about the ops behind these two tools.
For now: please check out the Commute Impact Calculator and tell me what you think!