Reliability of Stockholm Subway - Index of

Chapter 3: Methodology of data analysis
Reliability as it was mentioned above is quite a vague term which is not able to
provide us with a good specified and clear measure. In most cases under reliability
researches mean two closely related concepts: punctuality and regularity. Punctuality
of the service means how precise the operator adheres to the timetable. Regularity is
how regular the service is. Regular service is usually characterized with its frequency
and evenness of headways. Basing on the data stored in database of SL it is possible
to calculate several measures pertaining to punctuality and regularity.
3.1 Measures of punctuality
3.1.1 On-time performance
On-time performance measures the degree of trains‟ adherence to the timetable. The
unpredictable delays make service unreliable and less attractive to commuters
especially making time sensitive trips (e.g. to work, school, etc.). On-time
performance can be demonstrated as the percentage of trains that have departed ontime
or have been delayed. According to SL requirements, trains that depart in the
range from 60 seconds earlier to 180 seconds later are on-time. Thus, it is possible to
define three groups of data: trains that leave long before the departure time, trains that
are on-time, and delayed trains.
3.1.2 Deviation from scheduled departure
All the trains in Stockholm subway have to depart in accordance with timetable.
However in reality different conditions, such as passenger flow, driver‟s behavior,
technical problems, for example with signal and dispatching systems, weather and
others cause train delays or create situations when trains have earlier departure. One
of the parameters characterizing the schedule adherence of the service is the deviation
from scheduled departure which is a difference between actual departure time and
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