Service Reliability
We can’t improve service reliability without first accurately measuring it. To measure how reliable our service is for riders, we use different metrics for each mode. We use different metrics for each because they don't operate the same. These metrics also reflect how riders experience different modes.
Check back here in early 2025 to see more reliability data for the Green Line, Mattapan Line, bus, Commuter Rail, ferry, and The RIDE.
Subway Reliability
We determine the reliability of the Blue, Orange, and Red lines using two metrics: excess trip time and subway trip time. Each offers a different way to measure reliability:
- Excess trip time: The difference between a rider's actual trip time and their expected trip time
- Subway trip time: How many minutes it takes for a rider to travel from one end of a subway line to the other
Explore the data dashboards and learn more about each metric below.
Explore the Excess Trip Time Dashboard
Interact with the dashboard below to see average excess trip time on the Blue, Orange, and Red lines. Updates are published weekly on Monday mornings.
There are three main parts to this dashboard:
- The Average Reliability column on the left shows how many riders reached their destination within five minutes of the expected time. Higher percentages are better.
- The rectangular area chart shows the percentage of riders who arrived within five minutes and within 20 minutes of their expected time. Ideally, the line trends upward, and more color is better.
- The circles below the chart represent ridership volume. Larger circles represent high ridership, and smaller circles represent lower ridership.
How We Measure Excess Trip Time
Excess trip time (ETT) is the difference between a rider's actual trip time and their expected trip time. In other words, ETT compares how long a rider's journey actually takes to how long it should take.
We started using ETT to measure reliability in December 2024, as outlined in updates to the Service Delivery Policy. We now use ETT instead of our old metric, number of on-time trips, because it better reflects rider experience. We count a trip as "reliable" if ETT is five minutes or less.
In the future, we also plan to use ETT to measure reliability for the Green Line, Mattapan Line, and bus service.
Explore the Subway Trip Time Dashboard
Interact with the dashboard below to see average trip times for each subway line.
How We Measure Subway Trip Time
To measure trip time, first, we calculate the daily median trip time for the Orange and Blue lines in both directions, and each branch in both directions on the Green, Red, and Mattapan Lines. Then, we calculate the average of both medians from each of those lines to find each line’s daily average trip time. Finally, we calculate a seven-day average trip time for each line, each day. To do that, we find the average of the seven most recent daily average trip times.
As of summer 2024, trip time data is available for all lines.
