Data Sources — Trackser Live

The two feeds

Feed	URL pattern	Format
TrackerNet — `PredictionDetailed`	`api.tfl.gov.uk/TrackerNet/PredictionDetailed/{lineCode}/{stationCode}`	XML
Unified — Arrivals	`api.tfl.gov.uk/Line/{lineIds}/Arrivals`	JSON

Both are authenticated with a TfL app_key. TrackerNet is the primary, granular source — the same feed used in real-time train control — while the Unified API fills in the gaps TrackerNet doesn't cover.

The per-station polling model

This is the most important thing to understand about the data. TrackerNet's PredictionDetailed is queried per station, not per train. Each call returns a countdown of every train currently approaching that one station.

Trackser Live polls a fixed, curated list of stations per line. As a train physically approaches, it appears in the countdown lists of several nearby monitored stations at once — the same physical train, seen multiple times. A de-duplication step collapses those sightings into one record per train.

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A consequence worth knowing: polledStationName on a merged record is the station whose countdown won the merge — it is not reliably the train's next physical stop. Use currentLocation to anchor a train's true position.

Line coverage

All 11 London Underground lines are ingested, each with a hand-curated set of polled stations:

bakerloo   central   circle   district   hammersmith-city   jubilee
metropolitan   northern   piccadilly   victoria   waterloo-city

Associated and adjacent services are also handled where they share track or interwork:

Chiltern — runs on Metropolitan line track; always sourced from TrackerNet.
Lioness, Mildmay, Weaver, Windrush and the Elizabeth line — resolved where relevant to the app.

How the feeds are merged

Both feeds are merged into one set of trains per line.
For Underground trains, TrackerNet is preferred; its records carry source: "trackernet".
The Unified API covers TrackerNet's blind spots — such as the Metropolitan's Chesham branch and the Bakerloo / Lioness-shared Watford DC line. Those records carry source: "unified" and report the genuine next stop directly.
Metropolitan-line trains are further enriched with booked stopping patterns and platforms from the working timetable.

Refresh cadence

Feeds are pulled on the build cycle described in the architecture — a per-minute cron plus a +30-second alarm on each line's Durable Object, giving an effective refresh of roughly every 30 seconds.

Attribution & licensing

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