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West LRT traffic signal adjustment FAQ

The West LRT project is the largest infrastructure endeavour ever undertaken by The City of Calgary. With the addition of 8.2 kilometres of track between downtown and 69 Street S.W., you may have noticed changes in signal timings at some of the affected intersections. As frequently asked questions come up regarding these intersections and signal adjustments, we will do our best to address them here.

The City of Calgary would like to ensure Calgarians that safety is our first priority in the work that we do. We will continue to monitor and measure the signals and intersections that are affected by the implementation of the West LRT, we appreciate your cooperation. Please contact 311 with any comments or concerns.

  1. What does pre-empt programming mean?
  2. Why are the pedestrian or vehicle intervals being delayed?
  3. Why does the traffic signal turn to green just before the bells and lights start, and stay green until after the gates are fully descended? I find this confusing. Should I stop or go?
  4. I’ve noticed some of the intersections along the West LRT operate erratically, with gates going down and up right away as well as signals skipping intervals, why does this happen?
  5. It seems like there is a delay in when the walk interval is supposed to appear?
  6. Will the traffic signals be coordinated along the West LRT line?
  7. Why do I sometimes get a very short walk light?

Intersection specific questions:

1. What does pre-empt programming mean?
Preempt programming means when a train is approaching, the traffic signal prepares traffic at the intersection for the train’s arrival to ensure the tracks are clear of motorists and pedestrians. It also allows traffic moving parallel to the train to continue moving while the train proceeds through the intersection. The process often takes upwards of 1.5 minutes, meaning that these traffic signals are frequently operating in a preempted mode, even if a train is not in sight.

2. Why are the pedestrian or vehicle intervals being delayed?
At signalized intersections, where train tracks intersect with an approaching roadway, an additional green interval is required to ensure that the tracks are clear of all obstructions in advance of the C-Train’s arrival. C-Train arrivals can occur at any point during a traffic signal cycle, meaning a green signal interval for any traffic or pedestrian crossing can be interrupted when a C-Train is approaching. These factors combine to result in increased traffic and pedestrian delay. However, to minimize traffic and pedestrian delay, signal timings have been designed to return to specific points in the signal cycle depending on which interval was interrupted.

3. Why does the traffic signal turn to green just before the bells and lights start, and stay green until after the gates are fully descended? I find this confusing. Should I stop or go?
This green light period is only intended to clear traffic off of the train tracks to ensure there are no obstructions in the path of the C-Train. When you see the light change to green and your vehicle is on the train tracks or in the way of an LRT gate arm, please clear the tracks for your safety. For your own safety, you should not stop on train tracks if it can be avoided. However, the track clearance interval is designed in case a vehicle is unavoidably stopped on the tracks.

4. I’ve noticed some of the intersections along the West LRT operate erratically, with gates going down and up right away as well as signals skipping intervals, why does this happen?
Sometimes LRT intersections can act erratically due to train-generated pre-empt calls. While we cannot eliminate this type of pre-empt for safety reasons, we have worked with the West LRT team to reduce the occurrence of erratic pre-empt calls.

5. It seems like there is a delay in when the walk interval is supposed to appear.
The traffic signal timings have been carefully balanced to serve pedestrians as well as the high traffic volumes. However, as the LRT pre-empts the signal at different times, the time between pedestrian intervals can vary.

6. Will the traffic signals be coordinated along the West LRT line?
Unfortunately due to the LRT pre-empt, these signals cannot be coordinated. Coordination would result in very long delays for some other directions of travel, including pedestrians.

7. Why do I sometimes get a very short walk light?
When a train is approaching the intersection, walk times are ended immediately in order to ensure that the track clearance interval is served in advance of train arrival. Shortening the walk allows us to minimize the total preemption time and therefore serve pedestrians more frequently.

17 Avenue at Christie Park Gate S.W.

In 2015, the traffic signal controller was upgraded at this intersection to reduce pedestrian and motorist delay.

Why has the “turn on solid green” been removed at 17 Avenue at Christie Park Gate S.W.?
The “solid green” signal has been removed for eastbound left-turning traffic to minimize the potential for eastbound to northbound left-turning motorists to turn when a C-Train is approaching.

Will the pre-empted signals be coordinated between Sarcee Trail and Christie Park Gate at 17 Avenue S.W.?
Unfortunately, it is not possible to coordinate the traffic signals to be pre-empted along 17 Avenue S.W. due to the C-Train pre-empt.

Why are the signal timings so erratic at this intersection?
Traffic signals near the end of an LRT line are preempted by trains initiating a start sequence from that end of line station. These signals tend to operate less efficiently than other preempted intersections due to the additional variability in the time trains take to initiate their start sequence. Train operators leaving the station from the end of line are also more likely to initiate and then cancel their start sequence in order to leave at their scheduled departure time. This cancellation and re-initiation can result in what would appear as erratic traffic signal operation.

Why is the westbound to southbound left turn not served during preemption?
While a train is proceeding through the intersection, the westbound green interval is served with the eastbound green interval. While the westbound left turn interval is not served at that point, westbound left-turning motorists may turn during the permissive (solid green) interval when gaps in eastbound traffic allow them to do so. Considering traffic volumes at this location, this operation optimizes traffic flow.

17 Avenue at Sirocco Drive S.W.

In 2015, the traffic signal controller was upgraded at this intersection to reduce pedestrian and motorist delay.

Why is the westbound to southbound left turn served during pm rush hour preemption but not at other times of day?
While a train is proceeding through the intersection, the westbound green interval is served either with the westbound left or the eastbound green interval. The westbound left is served during the pm peak because traffic volumes are heavier in that direction. However, at all other times of day the eastbound traffic volumes are heavier than the westbound left-turning volumes. The westbound left is always allowed during preemption, but there rarely sufficient time to serve it. If the preemption is longer than usual (such as during a “two train” scenario), there may be sufficient time for both the eastbound through and the westbound left greens to be served before the preemption ends.

Will the pre-empted signals be coordinated between Sarcee Trail and Christie Park Gate at 17 Avenue S.W.?
Unfortunately, it is not possible to coordinate the traffic signals to be coordinated along 17 Avenue S.W. due to the C-Train pre-emption.

Why is the southbound left-turn arrow only served during a preemption?
This turn arrow is necessary to clear the C-Train tracks in advance of a train, but results in unnecessary delay to all other directions when operated with normal cycling. To ensure that queuing is minimized here, special signal timings (with increased southbound green time) are used at specific times of day/days of the week to address demand.

Why is my walk light not on when conflicting traffic is stopped?
Revisions have been made here to serve pedestrians to the best of our ability. However, when a train is approaching and the southbound “track clearance” is on, the intent is to clear vehicles from the LRT tracks. Pedestrians crossing at that time could block turning vehicles and potentially prevent them from clearing the tracks.

Bow Trail S.W. and 26 Street S.W.

In late 2014, the traffic signal controller was upgraded at this intersection to reduce pedestrian and vehicle delay and improve safety.

Why is the eastbound-westbound green interval shorter during rush hours?
Since West LRT opened, the number of pedestrians at this intersection has greatly increased. This, combined with the need to pre-empt signal timings to accommodate train traffic, meant there was a need to reduce the length of the green interval given to eastbound traffic.

Why is my green interval sometimes skipped or short?
This is due to LRT preemption interrupting the normal signal cycle. Preemption can shorten an interrupted green interval. When returning from preemption, this intersection returns to whichever motorists have been waiting the longest, which can result in the appearance that an interval has been skipped.

Why is walk time shortened or skipped?
This is due to LRT preemption interrupting the normal signal cycle. Pedestrian intervals may be skipped or the walk time shortened when a train is approaching. However, the full flashing don’t walk time is always provided.

7 Avenue and 11 Street S.W.

Why is the northbound-southbound green time so short and eastbound-westbound green time so long, at 7 Avenue and 11 Street S.W.?
The traffic signal timings at this intersection were designed to reduce the likelihood of northbound vehicles being queued from 6 Avenue over the tracks at 7 Avenue and 11 Street S.W. We did so by limiting the north – south green time so that this is unlikely to happen. Track clearance signal intervals are normally used to clear vehicles off of LRT tracks in advance of train arrival when traffic queuing is a concern. However, due to the frequency of the C-Train and the distance between these two intersections, a pre-empted light cycle is not possible. We will be monitoring the operation of this intersection to determine if the timings can safely be adjusted.

17 Avenue at 45 Street S.W.

Due to the implementation of the West LRT, the eastbound left hand turn from 17 Avenue to 47 Street S.W. was removed. To allow for additional turning opportunities, a left hand turn signal was installed for vehicles moving from eastbound 17 Avenue S.W. to northbound 45 Street S.W.

Before this eastbound left turn signal was added, a left turn signal already existed at this intersection for vehicles moving from westbound 17 Avenue S.W. to southbound 45 Street S.W. Because there are no turn bays at this intersection, these arrows cannot operate together. Instead, these arrows operate on alternate signal cycles. This means that each direction will get an arrow indication every second signal cycle, rather than every cycle.

What are the traffic volumes at this intersection?
During the morning rush hour traffic times (7 a.m. – 9 a.m.), the through travel direction with the highest volume, which is eastbound 17 Avenue S.W., carries approximately 1000 vehicles per hour. The eastbound to northbound left turning volume is approximately 100 vehicles per hour. When looking at vehicles moving in the opposite direction, westbound 17 Avenue S.W., this carries about 350 vehicles per hour, making the turn difficult without an arrow, and delaying both turning and through traffic in the shared lanes.