There is no bridge across the Yukon River at Dawson City, Yukon. Instead, travelers must use the George Black Ferry, a diesel powered barge that hauls cars, trucks, and RV's back and forth across the river. The George Black Ferry is a free service that runs 24 hours a day in the summer season, but shuts down in winter when the river freezes.
If you go:
Try to time your crossing to avoid the peak travel periods, which are from 7 to 11 AM for westbound travelers on the Dawson City side of the river, and from 2 PM until 7 PM for travelers on the east side of the river who are headed into town. The ferry can only haul a dozen or so vehicles at a time, so the wait during those peaks can be as long as three hours. The actual crossing only takes about six minutes. Service stops in mid-October, and resumes in mid-May, after the spring thaw. Call ahead for exact seasonal dates, which can vary from year to year.
Links:

Top of the World Highway
Top of the World Highway
Dawson, Yukon Territory Canada
Phone Numbers:
Ferry Information
+1 (867) 993-5566
+1 (867) 993-5566
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