# How long you actually wait

> The gap between trains, measured rather than timetabled.

- Category: Transport
- Cadence: live
- Status: Live: values change continuously; cite the retrieval time.
- Dataset key: `live-headways`
- Source: [TfL Unified API](https://api.tfl.gov.uk/)
- Licence: TfL Open Data Licence — [terms](https://tfl.gov.uk/corporate/terms-and-conditions/transport-data-service)
- Canonical page: [https://londongraph.com/g/how-long-you-wait](https://londongraph.com/g/how-long-you-wait)
- Machine-readable record: [https://londongraph.com/data/how-long-you-wait](https://londongraph.com/data/how-long-you-wait)

## Methodology

Median gap between consecutive arrivals per line, computed from live predictions across every station reporting at least four of them. Gaps over twenty minutes are discarded as the end of a timetable window rather than a service interval. A line can run plenty of trains and still make you wait if they are bunched, which is what this measures and a train count does not.

## Visualisations

- [Overview](https://londongraph.com/g/how-long-you-wait): The gap between trains, measured rather than timetabled.
- [Network map](https://londongraph.com/g/how-long-you-wait?view=network-map): Colour each Underground line by its measured median headway.

## Citation guidance

Attribute the original publisher named above and identify LondonGraph as the visualisation and methodology layer. Do not describe live values as a historical census, and do not present placeholder values as observations.