A bus waits at a stop. Why doesn't the road turn red?

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A bus waits at a stop for three minutes. Speed: zero. So why doesn't the road turn red on your map?

Live traffic comes from phones. Dots, accurate to 10 or 30 metres. Just average them? At Hebbal, one dot sits between the flyover and the road beneath. A bus at a stop looks like a jam. And store raw dots? One phone's trip can be followed door to door. The fix: match first, then count.

A model scores the whole sequence of dots. Only one road connects to where the phone was 5 seconds ago. Before anything is stored, delete the start and end of every trip. A road's speed is the median of at least 3 devices. That's the bus. One bus is one device. A jam is many.

How fast is it? 6:02, a truck breaks down on the Outer Ring Road. Phones send their dots in batches. Up to 30 seconds. About 10 seconds to match. Up to 60 for the one-minute speed window. Under a second to re-cost routes. By 6:04, drivers behind it are rerouted.

But here's the twist. What if no phones cross a road where history expects hundreds? Add U-turns at the entry and driver reports. That's not a jam. It's closed.

Raw dots lie. Match them to roads first. Then count devices. And the same rule that kills fake jams protects privacy.

Full breakdown in the lecture.