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WASHINGTON (AP) - Metro says all of the system's trains had to be stopped for a second time after a computer system crashed.

The second stoppage occurred around 12:30 a.m. Sunday and lasted until around 1 a.m.

The Washinton-area subway system also shut all its trains down shortly after 2 p.m. Saturday. That stoppage also lasted half an hour.

Metro spokesman Dan Stessel says the computer issue affected Metro's ability to see where trains were on the lines. He says trains in motion continued to their next stations, then sat with the doors open until the problem was resolved.

Stessel says the shutdowns were ordered out of "an abundance of caution," adding that the signal system - which ensures that trains maintain enough space between them - remained operational.