here's the BS from the FAQ:
Controlled Crossings
This stunning Marathon route takes runners through the Vancouver neighbourhood of South Granville and Kerrisdale along West 49th Avenue. While beautiful, it is challenging because runners must cross two of the most significant arteries into Vancouver and as such, we are required to work with the police and transit authorities to permit emergency and transit access.
Our plan is to release runners in waves at the Start Line thereby creating natural breaks at these intersections. By doing so, we will work with our city partners to coordinate a timely crossing of runners while permitting some emergency and transit access.
PLEASE NOTE, at 49th Avenue at both Oak Street and Granville Street, our traffic plan calls for a controlled crossing, allowing buses only – and if needed, taxis and emergency vehicles – to cross, with regular vehicle traffic diverted before the intersection. For the safety of all participants, please obey officer and volunteer instructions at these major street crossings. Timing mats are placed at these key intersections and times for runners who experience any delay will be adjusted by our timing supplier, Sportstats.
To avoid any potential stops, please also seed yourself in the appropriate time corrals when registering. Runners are released in waves, factoring in average paces for each corral.
Safety is everyone’s top priority. Thank you for your understanding."
I'd say they lie about it in the FAQ. I also do not see how seeding yourself in a corral helps to avoid traffic interruption, considering they were happening every minute or two.