Union Pacific Railroad has raised the roof on 15 of its tunnels over Donner Pass in the Sierra, allowing double-stacked trains to cross the pass and go through Reno for the first time on the way to Chicago. Double-stacked trains have been routed through the longer and more difficult Feather River Canyon north of Reno. … Union Pacific spent about $2.6 billion in the past year to improve its rail system while business was slow because of the recession.