(Portland, OR) -- Today marks day four of MAX trains being shut down due to severe winter weather. TriMet says all MAX service remains suspended this morning amid forecasts of freezing rain. Officials say a combination of trees falling across tracks and power lines, power outages, and ice on the tracks are keeping the trains from running. TriMet says it will have shuttle buses replacing trains on all of its MAX lines. Meanwhile, TriMet buses will be running on all scheduled bus lines, though some buses will continue to be running with snow chains, limiting their speed to 25 miles per hour.