Below is straight from the City Report which can be found
https://eagenda.burnaby.ca/sirepub/cache/2/nnuhymhqflnelc2vgp4mzhaf/147901272020100145314.pdf.
"Trains destined for the single-track Thornton Tunnel must queue until the tunnel has been ventilated after the passage of a preceding train. This queuing currently takes place east of Douglas Road, where the adjoining land uses are primarily industrial and park. The queuing presently cannot take place closer to the tunnel because a stopped train near the tunnel would extend across Douglas Road, blocking the crossing for an unacceptably long time."
"The sound of a train starting or stopping is far noisier than that of a train moving. A train has a small gap between each car. When a train stops, that gap disappears and each car impacts the one ahead of it. The sound of impact runs from car to car along the length of the train. The process for starting up again is similarly noisy."
"As a result of constructing the Holdom overpass, this starting and stopping activity will move westward to Willingdon A venue, and thus be located close to residential developments in the Brentwood Town Centre. The magnitude and extent of these effects is not yet known, nor has it yet been determined whether or not it is possible to mitigate them.
"The project will also cross the riparian area of Still Creek, at a location that is already urbanized. Some mitigation of the impact to the creek may be needed"