Measuring and Illustrating Headway Reliability

In recent articles, I have reviewed a pervasive problem on the TTC’s network with uneven headways (the time between vehicles). This is annoying enough in “normal” times, but with the concerns about crowding during the pandemic, anything that contributes to crowding is more than just an annoyance.

The CEO’s Report presents only a few measures of service quality:

  • the proportion of service that is “on time” leaving terminals,
  • the number of short turns, and
  • the amount of service fielded compared to what is scheduled.

These metrics are utterly inadequate to showing how the system is behaving at the level seen day-by-day, hour-by-hour by riders for several reasons:

  • Most riders do not board vehicles at or near terminals, and measures that look only at terminal performance do not reflect most of each route.
  • “On time” is a meaningless concept for most routes because service is (or should be) frequent enough that riders do not time their arrivals at stops to meet their bus.
  • A count of short turns only indicates that most vehicles reached their terminals, not whether the absence of short-turns contributed to poor service quality. Moreover, there is good reason to believe that the number of short turns is under-reported.
  • Statistics are averaged on an all-day, all month basis and do not reflect route-by-route or hour-by-hour variations.

Riders to not ride “average” buses and streetcars – they take what shows up when they try to use the system. Indeed, if the TTC actually provided “average” service, a lot of problems would be solved because the service would be much more reliable.

At the recent TTC Board meeting, CEO Rick Leary noted that the metrics in his monthly report will be changed in the near future. This is long overdue, but it remains to be seen just how informative these will be.

This article includes displays of headway reliability in a new type of chart I have been working on recently. Reader feedback on this is welcome.

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