A highway camera photo shows traffic in FortMcMurray jammed in the southbound lane of Highway 63 on the north side of the Athabasca River. The image was captured at 3:11 p.m. MT, about an hour after an evacuation order was issued for four neighbourhoods. (511 Alberta)
Evacuation order issued as wildfire threatening Fort McMurray draws closer https://www.cbc.ca/news/canada/edmonton/alberta-wildfire-grande-prairie-fort-mcmurray-1.7203695
More lanes == less traffic is wrong due to induced demand. In an evacuation, however, the demand is already at its maximum. What you want is more throughput to get the people out.
Having less lanes won’t make people choose going on train or bus instead. Chances are that the busses and trains are already full.