The Dallas Area Rapid Transit authority (DART) in the US has opened the first three miles of the new $1.8bn 20-station 28-mile Green Line.
The newly opened section extends from Pearl on the east side of Downtown Dallas to MLK and covers four stations.
The remaining 25 miles of the Green Line are scheduled to open in December 2010 and will link North Carrolton/Frankford in the north-west with Buckner in the south-east.
Once fully opened, the Green Line will be the longest light rail expansion in North America.
The Green Line is being funded by $700m from the Federal Transit Administration and $78.4m in funds from the American Recovery and Reinvestment Act.
The Green Line, which joins the existing red line and blue line rail operations, is part of the $3.3bn DART light rail expansion project to double its network to 90 miles by 2013, covering 62 stations.
Another line of the project, the Orange Line, is under construction.