October 19, 2015, 1:14 pm
Ever waited for the SkyTrain during scheduled single track night time service?
If you are a regular rider, chances are you have. Chances are you’ve also asked yourself what exactly is going down during single tracked service.
Well, I’m here to shed some light! Single tracking on the Expo Line has been used accommodate the Power Rail Replacement work currently underway on the SkyTrain.
The project is nearly 80% complete and we thought it would be cool to get the skinny on the power rail replacement as well as how single tracking works.
We checked in with Ian Fisher, Manager of Operations at BCRTC, to learn the ins-and-outs of single tracking.
What is the power rail replacement project that’s underway during single tracking hours?
For over the last year BCRTC has been accommodating a power rail replacement project that will help maintain and improve system reliability and allow for increased capacity in the future. The new power rail replaces worn power rail installed when the system was new and will support operation of more and longer trains, as well as increase energy efficiency. The power rails are mounted vertically to the side of the track and supply 600 volts DC to the trains (one rail is +300 V and the other -300 V). The need to replace them is due to the same factors that control how many appliances you can plug into an extension cord – too many and the cord will overheat while also increasing its electrical resistance.
What is single tracking and how does it work?
“Single-tracking” is when we run trains in both directions over a single piece of track. It’s like taking a two-lane road down to one lane and having a signal or flag ,person regulating traffic in the remaining lane so it only flows in one direction at a time. Many railways operate this way where they do not have two tracks. We do this when work or an incident on or adjacent to one track requires it to be closed while the other track can remain open for passenger service.
The length of single-tracking will depend on the locations of the track switches where we can transition from normal operation to single-tracking, and vice-versa. This can be short or long. For example, if we have to detour trains around the westbound platform at New Westminster, the length of the single-tracking area is only about 500 metres. At the other extreme, if the eastbound platforms at Main or Broadway are closed, the single tracking area is about 5 km long – from just east of Stadium-Chinatown to west of Nanaimo.
The longer the area, the more time it takes trains to travel through the area and trains operating in one direction may need to wait for trains in the opposite direction to clear the single-track area. In the Nanaimo to Stadium example the travel time between the switches is about 7.5 minutes in each direction. As a result, if trains ran alternately in each direction, we could run a train each way about every 15 minutes – significantly less often than the 5 minute service normally offered in late evenings. This would give a service of 4 trains/hour and so provide capacity for about 2,000 riders per hour in each direction.
We can increase capacity by running trains back-to-back in the same direction through the single-tracking area. This occupies the line for a bit more time for each direction (about 90 seconds each way) but overall the capacity is increased since we can then run two trains each way about every 18 minutes. The result is 6.7 trains per hour in each direction, with a capacity of 3,300 passengers. We have generally found this “two train platoon” approach to be effective at balancing capacity with service frequency and have used it for almost all of the power rail work areas in 2014 and 2015.
In order to better balance the number of passengers on each train, and to provide a more consistent service on the rest of the network, we run the trains a bit further apart outside the single tracking area. So, in the example above, the first westbound train operates about five minutes ahead of the second until it gets to Nanaimo. The first train then waits at the platform until the second train has caught up, then proceeds towards the start of the single-tracking area. With the two westbound trains now running back-to-back, they can enter the single-track section as soon as it is clear of eastbound trains. When leaving a single-track section, we may have the second train wait for a few minutes at the first station after the single-track section to help space the trains out for the same reasons. In this example, this occurs for eastbound trains at Nanaimo.
Why can’t work be done during non-service hours to avoid single tracking?
Doing the power rail work after service ends is not feasible since the time when no trains are running between the last train of the night and the first train the next day is too short for reasonable productivity and a 2-year project with work starting mid-evening would take 10 years or more if all work was after service ends. Consequently, we design single-tracking operations that allow the work to proceed on one track while the other track remains available to trains. This is done for other projects that need extended track access as well, such as repair and replacement of the running rails that the trains operate on, and for some types of work in stations.
How is single tracking monitored to ensure safety?
BCRTC Operations Planning staff develop finely-tuned timetables that aim to squeeze as much capacity as possible out of each single-tracking area. Train timings are carefully worked out to ensure that trains are running pretty much continuously in one direction or the other through the single-tracking area and the operation tested in simulation. While our signalling system would never let two trains collide, staff in the control centre must remain vigilant after delays to ensure that trains operating in opposing directions do not meet in a single-track area – a situation that requires one of the trains to be reversed clear of the single-track area to clear the deadlock.
A variation on single-tracking that we also use at times is to “break” the train operation at a station, such that trains from both directions terminate at a platform alternately but through service is not provided. This effectively creates two shorter single-track sections and thus allows a higher frequency of service to be provided on each, and can be easier to operate. As an example, we may operate trains from VCC-Clark to one of the platforms at Gilmore and back, while other trains operate from the same Gilmore platform to Waterfront and back. Through passengers thus change trains at the same platform – an important consideration on the Millennium Line where most stations have side platforms.
We continuously balance the need to see to work completed with the impact on service and customers. As a result we delay the start of single tracking on game/large concert nights so that additional trains can be operated to clear the crowds. If the event is particularly large, or will end later than 10:30 p.m., we generally cancel the single-tracking that night to provide a higher service level.
Thanks Ian for giving us the lowdown on single tracking! If you want updates about where we are with Power Rail Replacement work, you can check out OnTrack on our website.
Author: Laura Tennant