A power outage Monday morning shut down light-rail trains and delayed commuters throughout the Portland region.

The Oregonian reported the disruption in the downtown area backed up TriMet trains in the suburbs. By the end of rush hour, two of four lines remained disrupted.

TriMet spokeswoman Robert Alstadt said the problem was caused by electrical system work. TriMet is building a line to the southeast, and the work was to tie the expansion line into the existing system. She says crews were still trying to troubleshoot the problem Monday.