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I'd love to know the answer as well. Any trip far enough to warrant checking traffic conditions at the outset surely warrants traffic updates and rerouting.
 
I took a long trip last week that had a few optional route legs. After a stop, which had forced a recalculation of the route, I noticed that the route had changed on Google Maps due to traffic around DC beltway. I don't know if the recalc would have happened if we hadn't veered off the route for a few minutes.
 
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