Thanks for sharing, Amelia!
I've biked the Eastern Trail through the marsh, but not Route 1, because I like my life and want to keep it. Here's a screenshot from Google Maps. There's no reason for this road to be four lanes. I've driven this stretch occasionally, though I can't remember ever seeing it congested. If I'm not mistaken, it was overbuilt back before the Maine Turnpike was finished, and most of the state through traffic moved to 95 after 1950. So, one could also argue there's no need to have two four-lane highways parallel to each other.
Making a safe route for someone biking or walking from Dunstan to the south part of Route 1 in Scarborough would cut the non-car travel distance and time in half. Walking from the Dunstan neighborhood (which actually has a bunch of homes) to, say, the Holy Donut in Scarborough, would cut the one-way trip down by about 45 minutes. I'm not sure drivers are saving 45 seconds by having an extra travel lane.

