Please be aware that Washington has multiple airports and that these results are only for Dulles International airport.
At Washington the most flights depart around 12:00. (Hourly flights, based on 377 datapoints.)
From Washington it is on average the cheapest to fly to Brussels and to London. (Average prices, based on 70 datapoints.)
From Washington most of the flights depart to New York, second best connected from Washington is Toronto. (Daily flights, based on 85 datapoints.)
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