FARGO, N.D. -

Heavy freight traffic is hampering Amtrak passenger trains between Chicago and the Pacific Northwest.
    
Spokesman Marc Magliari says Amtrak is canceling or altering many of the Empire Builder trips between Chicago and Portland, Ore., through Sunday as a result of the congestion on the tracks that Amtrak shares with BNSF Railway.
    
He says hundreds of travelers are affected. Amtrak is offering to rebook trips.
    
Much of the congestion is due to heavy freight train traffic in the western North Dakota oil fields. BNSF spokeswoman Amy McBeth says the recent cold snap also has been a factor because it has slowed everything down.