Your FASTag is read 37 times. You pay once.

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Your FASTag just got read 37 times at one toll. So why were you only charged once?

A truck crawls behind a bus. The antenna reads its tag 37 times. Two of those reads came from the next lane's antenna. The barrier lifted once. So which reads are the crossing?

Group reads by a time window? A jam can last minutes. One slow truck becomes several crossings. Several debits. Use the road instead. A loop detector marks enter and leave. And the lane whose loop and barrier saw the truck wins.

37 reads become one passage. That passage gets one transaction number. Minted once. The plaza was offline. It resends the file later. Maybe twice. The acquirer has seen that number before. Dropped. Only the first copy reaches the issuer.

But here's the catch. Same tag, a plaza 400 kilometres away. Two minutes apart. That's 12,000 kilometres an hour. Over 120 kilometres an hour, NPCI calls it near time. A cloned tag.

The lane drops radio repeats. The acquirer drops retries. The issuer flags the impossible. And you pay once.

Full breakdown in the lecture.