How this monitoring works

Two different things are often confused. A line can be running badly late while its real-time data is perfectly healthy — the countdowns are accurate, they are just counting down to late trains. And a line can be running normally while its data freezes, leaving countdowns wrong even though service is fine.

This site only reports the second thing. MTA service alerts are displayed alongside each line for context, but they never change a data-health verdict.

Every official MTA subway real-time feed is retrieved from our own servers roughly once a minute, decoded, and then analysed separately for each line it covers. The primary signal is whether the arrival predictions themselves keep changing. Vehicle position timestamps are used as supporting evidence only, because they can keep ticking even when arrival predictions have frozen.

We also record how many trips and upcoming stop arrivals a line is publishing, and compare each line against the other lines in the same feed to tell a single-line problem apart from a whole-feed one.

Avoiding false alarms matters more to us than being first. A single odd check never changes a public status: a line must look wrong across several consecutive checks before we report anything, and it must look healthy again for several consecutive checks before we call it recovered.

Services that genuinely stop running — overnight patterns, rush-hour-only expresses, shuttles — are marked “Not Scheduled” rather than broken, using observed service baselines and the MTA's own alerts about suspended service. Shuttles and the Staten Island Railway update less often by nature, so they are held to a slower expectation.

• ✓Operational

  Real-time arrival information is current and updating normally.

• ⚠Degraded

  Real-time arrival information is available but updating less consistently than expected.

• ⚠Stale

  Real-time arrival information is no longer refreshing, so countdowns may be out of date.

• ✕No Real-Time Data

  No real-time arrival information is currently being published for this service.

• –Not Scheduled

  This service is not running right now, so no arrival information is expected.

• ✕Source Unavailable

  The published MTA data feed for this service could not be retrieved.

• ?Status Unknown

  There is not enough recent information to confirm a status.

Today this page covers NYC subway service, the shuttles and the Staten Island Railway. Long Island Rail Road and Metro-North feeds are monitored internally but are not published here until we have validated how their data behaves.

We can only observe what the MTA publishes. If a feed reports confidently wrong information, it will look healthy to us. And if our own monitoring stops running, the page says so instead of pretending everything is fine.