I didn't mean to bring up history!
It was the Alaska-Canada Highway shortened to "Alcan". This was in some of the information during the 50th anniversary. Tricia Brown has much of the history in her book "The World-Famous Alaska Highway.
I do not remember when the big name change was. I believe it was right after the 50th anniversary. In Tricia Brown's book it says about 1971 when The Yukon Department of Highways and Public Works took over maintenance in the Yukon Territory. The US stopped funding part of the maintenance.