What Causes Subway Delays?

The TTC’s Andy Byford recently committed to a major reduction in subway delays by 2019 thanks in large measure to the introduction of a new signal system on Line 1 Yonge-University-Spadina.

Can this level of reduction actually be achieved? To get a sense of this, we must look at the actual delay reports from the TTC to see the location and type of service interruption. If a problem only account for one quarter of all delays, then a three-quarter reduction in delays cannot possibly be achieved simply by eliminating this class of problem. Similarly, if half of the delays are on one line, and a new technology is implemented on another, then nothing has been done to address delays on the untouched part of the system.

The TTC reports overall reliability statistics in the CEO’s report, but these are (a) not subdivided by cause and (b) use a measure of service “reliability” that would give a perfect score even if a large proportion of the service were missing. As long as trains are close enough to each other, even if there is one gap leading the pack or all of the trains crawl along the line, they do not count against the metric the TTC used for years to report service quality.

The counts below were calculated by reviewing all of the TTC eAlerts for service interruptions on the four rapid transit lines for January 2016. Anyone who reads these alerts and rides the system regularly knows that some delays never make it to an alert, but this is the best we have for published information.

Type of Delay                    Line 1    Line 2    Line 3    Line 4

Passenger Alarm                   6  16%   14  23%    2  18%
Signals                          11  30%   11  18%              3  60%
Mechanical                        1   3%    4   7%    8  73%    1  20%
Track                                       3   5%
Switching                                   1   2%
Security                          5  14%    6  10%              1  20%
Police Investigation              3   8%    4   7%
Fire Investigation                3   8%    8  13%    1   9%
Medical                           3   8%    4   7%
Power Off                         4  11%    3   5%
Unauthorized at Track Level                 1   2%
Late Clearing Work Zone           1   3%    1   2%
Unspecified                       0         1   2%

Total                            37        61        11         5

The details of the incidents are in the following table.


This is only a one month sample, and there are bound to be somewhat different numbers for other periods, but this gives the flavour of the situation.

Signal problems, annoying though they may be, account for only 30% of the delay incidents on the Yonge line, and 18% on the Bloor line for January 2016. That said, these tend to be the most long-lasting incidents and so their effect is greatly out of proportion to their number. Moreover, the incident count is higher on the Bloor-Danforth line by a wide margin. The new signals on Yonge-University will certainly improve conditions on that route, but delays overall will not be a thing of the past.

If the TTC is going to shoot for improvements, then they must start reporting their delay statistics at a more granular level so the a link will be visible between the type of “fix” undertaken and the location and type of delay whose stats go up or down. This would be a much more useful measure both of service quality and of the effects of management programs to improve the quality of transit service.