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Average Daily Subway Delay represents the total amount of delay in the subway, and the relative amount of delay compared to 2019 averages. The 2019 averages were deemed an unacceptable quality of service that are used to assess the impact of delays in recent months on the quality of service.
Trains typically spend about 20 seconds in stations when boarding and alighting passengers, this value only changes by plus or minus five seconds between a busy, crowded platform and an empty platform. For this metric, every second that a train spends stopped in the subway between two stations, or stopped at a station longer than 40 seconds, is counted as a second of delay. The Average Daily Delay and Variability chart shows a monthly average of the total amount of delay per day (black line), inside a blue cloud which represents the variability of that data over a month (one standard deviation either side of the average). This value represents the sum of delay each day due to all causes (vehicle breakdowns, train control issues, track/wayside equipment problems, medical emergencies and congestion). Due to the way the data are collected, it is not possible to separate out the causes of delay. With that said, this dataset is the only delay dataset that includes the delay due to congestion. The second chart compares delay in recent months to the average delay in 2019, to assess whether the impact of subway delays is significantly degrading quality of service. This view of the same data better illustrates how close we are to returning to 2019 conditions – which we consider to be an unacceptable level of delay.