Came across this video of a Coquitlam-bound M-Line trains using Platform 1 at Lougheed dated March 15, 2017:
• Video Link
Vancouver-bound M-Line train using Platform 3 at Lougheed on the same day
Looks like Expo Line trains still used Platform 2 - so westbound trains were split between 2 platforms.
• Video Link
No wrong-railing that day!
Notice how the Expo Line train leaves Platform 2 and the M-Line train leaves Platform 3 soon after - both westbound.
Maybe it was a test to maintain short headways? (instead of westbound trains lining up/waiting at Platform 2?)
The M-Line train arrives at Production Way as the Expo Line train is leaving.
Platform 2 could be Expo Line to Production Way and Platform 3 M-Line to VCC-Clark.
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Here's the regular eastbound pattern to Platform 3 at Lougheed (and wrong-railing to Burquitlam):
https://youtu.be/ejjAGaSdTt4