Yonge Subway Headway Study 1988 (Part 2)

This thread began with an introduction to the “problem” of capacity at Bloor-Yonge Station which dates back to the 1980s, an era when all expansion of capacity for travel from the suburbs to downtown was assumed to be on the subway network.  If you accept that premise, then it follows that massive expansion of subway capacity is absolutely required.  However, as we have recently seen from demand projections by Metrolinx, when there are good alternatives to the existing subway, people may find other ways to get downtown.

In this section, I will present another chunk from the long Chapter 3 in the TTC’s 1988 study.  This part includes descriptions of four ways to achieve shorter headways on the Yonge line through signalling changes.

Chapter 3 Option 1A discusses minor changes to the signal system needed to get headways down to 122 seconds.  Two critical issues are:

  • Keeping dwell times at Bloor Station at or below 45 seconds
  • Achieving a 122-second headway through Finch Terminal

At Bloor, this option proposes dispatching trains not from Bloor (as is done now), but from Wellesley northbound and Rosedale southbound.  The idea is to maintain a regular headway at Bloor (and hence dependable loading times), but this assumes a regular supply of trains to be dispatched toward Bloor Station.  If trains are arriving at bunches at Bloor before the change, there is a good chance they will still arrive in bunches nearby afterward.

As for Finch Terminal, the report concludes that a 122-second headway is possible, with difficulty, but definitely with “drop back” crewing where crews step back one or two trains at the terminal, and a fresh crew is always available to take a train out as soon as it arrives.  This scheme has been implemented on-and-off over the years depending on availability of operators.  However, problems stil arise with crews who are not ready to take their trains out the moment signals clear, and any assumption that good dispatching could be sustained through peak periods is on shaky ground.

Chapter 3 Option 1B discusses changes needed to get down to 112-second headways.  As with option 1A, drop back crewing would be used at Finch, although the need to operate this with razor-sharp timings gets more important as the headways get shorter.  Indeed, the TTC’s feeling is that this could not be achieved without using a second pocket track north of Finch for turnarounds.

The track layout for this operation is shown in Exhibit 3.3.3.  One drawback of this arrangement is the increased running time needed for trains to drive north, reverse, then return onto the southbound platform at Finch.

Changes would be made to signals at several locations on the line where the existing arrangement prevents trains from running this close together.

Finally, the 112-second headway would also require reconstruction at Bloor-Yonge to get the dwell times down to 30 seconds.

Chapter 3 Option 1C describes the changes needed to get down to 105-second headways.  This would require an aggressive change in the existing signalling system and a reduction in operating speed due to the close spacing of trains.  It is not recommended.

Chapter 3 Option 2 describes an Automatic Train Control system.  Remember when reading this that the technological framework is twenty years old, but the general discussion remains valid.  Only by moving to ATC with a moving block, computer-controlled signal system (such as on the RT), can trains be operated on extremely close spacings.

As with option 1C, the operating speed of the line would actually decrease because there would never be enough clear space in front of any train for high speed operation during peak periods.  Moreover, there would be no “stacking” space for trains during periods when actual running times are less than the scheduled values.  Today, we see terminal queues because trains often have more running time than they need.  Only two trains can fit in a terminal at once, and the excessive time is burned up in a queue approaching the terminal.

In an ATC environment with very close headways, all trains would have to operate on a set timetable with standard dwell times at stations to avoid bunching.

One change since this report was written is that the signals on the original Yonge line are now over 50 years old and must be replaced.  The decision to convert to ATC, at least on the oldest part of the line, therefore has no aspect of discarding existing technology before its time.  Whether we will ever need to get down to a 90-second headway, the signal system will cease to be a constraint once the technology is implemented over the entire line.  That’s a long way off.

In the next section, we will look at the fleet and carhouse requirements of the service increases for these options.