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I've worked around this by setting a reoccurring meeting to go home with my address in Google Calendar, my phone tells me beforehand when I need to leave in order to get home on time. I don't know if it includes traffic in its estimates but I've never been late (give or take a couple minutes).

Doesn't Google Now sort of offer that functionality (I take the train so it doesn't tell me that but it always tells me the distance to home/some event/work)

You could write your own traffic RSS feed and use that as a trigger.