Analysis of 512 St. Clair, January 2010 (Part 4: Intersections)

When I started the analysis of the TTC’s vehicle monitoring data some years ago, my great hope was to be able to analyze behaviour at stops and intersections.  Alas, the quality of data on the “old” version of the TTC’s system was utterly incapable of this type of use for two reasons:

  • Although vehicle position was polled every 20 seconds, vehicle location was resolved to a nearby intersection, and reported only sporadically.  This made fine grained location analysis impossible.
  • A location, such as a major stop, might not be reported at all for a vehicle’s trip, only the vehicle’s appearance at two nearby locations on either side of the point of interest.

With the new GPS-based data, position information is available for almost all vehicles every 20 seconds.  Anything that causes a vehicle to stop for some amount of time will be registered by a failure to change location in two or more succeeding data points.  (I say “almost” because some GPS units are a tad unreliable, and they report rogue data points causing missing samples in otherwise clean data.)

A great debate about St. Clair (and other routes with the same arrangement for left turns and farside stops) focuses on the following sequence of events:

  • Streetcar approaches an intersection and is caught and held by a red signal.
  • Streetcar waits for the red phase, and the following left-only phase to complete.
  • Streetcar moves through the intersection, serves a farside stop, and then departs.

In some cases, there is no stop associated with a traffic signal, but streetcar service may be held by it in any event.  In theory, approaching streetcars are supposed to extend their own green time, or to shorten the cross-street’s red, but empirical observation suggests that this does not always happen.

This article reviews several intersections on St. Clair to determine how transit-friendly the traffic signals actually are, and whether any change in their behaviour was visible over the month of January 2010 while many aspects of the line’s operation were still being adjusted.

An obvious and troubling observation from these data is that in general, streetcars spend more time waiting for green lights than they do serving the farside stops at the same locations.  This shows the frustration and inefficiency from an arrangement where cars must stop twice because they do not get the so-called transit priority they are supposed to receive at major, and even some minor, locations.

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