Hundreds of commuters taking the Red Line on Dubai Metro were delayed during rush hour on Tuesday because of a "precautionary procedure" that overran, the emirate's Roads and Transport Authority has said. An official told <em>The National</em> that the department was running a test on one of the trains at Union Station, after detecting a technical issue, but the safety procedure took longer than expected and caused a knock-on effect, compounding delays for commuters. "It was a minor four-minute delay but it was the rush hour and the station was busy," said the official. Karama station and ADCB station were also among those affected by the tests. The rare delay is believed to have begun at about 7am with commuters taking to Twitter to share their angst. Pictures of commuters crowding hallways were posted online and parents complained that they were late getting their children to school. Some tweeted that they were forced to take alternative transport to avoid further delays. Others suggested that commuters take the Green Line to BurJuman instead. The RTA was quick to resolve the issue, though the knock-on effect caused crowding at some stations for a few hours. Dubai Metro was officially opened on September 9, 2009 by Sheikh Mohammed bin Rashid, Vice President and Ruler of Dubai. It now facilitates more than 200 million journeys a year.