This thread hasn't been dormant nearly long enough to qualify as a zombie, but there's been no follow-up from the OP.

However, this:

route9active.org/

flipped over my transom. It's directly relevant to this thread. (For those from Away, the villages are listed north-to-south and include the OP's proposed commute.)

If the past is prologue to the future, I don't expect the pace of either planning or execution to be brisk. Further, the dimensions (narrow lanes / no shoulders) of Broadway / Route 9 constrain what can be done. But maybe there's hope.

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FBinNY: your suggestion to consider Metro North trains between Dobbs Ferry and Tarrytown is interesting, but Tarrytown's station is more than a mile north of White Plains Rd / NY 119, the OP's apparent destination. Further -- perhaps you've biked it -- heading east from Tarrytown's station to Bwy starts with a surprisingly steep climb.