Most people who start thinki9ng of commuting, pick routes they would take with their car. Is there no side streets that cars find too inconvenient/slow that you could use? I add a few miles and another 400 ft of climbing in order to take a less busy route.

You mention sidewalks....avoid them if you can. Learn to ride a bit more aggressively in the road and not get forced onto the sidewalk. Where I live, its against the law to ride on the sidewalk, even though many do.