The motion, part of a lawsuit filed by grassroots group Neighbors for Smart Rail, said construction of the Expo Line had not properly factored LRT's impact on traffic or potential impedance of emergency vehicles.

The court's decision, made late Wednesday, did not include a written opinion. Lower courts also had previously rejected the motion.

In a statement Thursday, Expo Board Chairman and Los Angeles County Supervisor Zev Yaroslavsky said the decision reinforces the "efforts to build a modern transit system on track. "

"We appreciate that the California Supreme Court is allowing construction of Expo Phase 2 to continue," said Expo Construction Authority CEO Rick Thorpe. "We're continuing to make significant progress in extending light rail from Culver City to Santa Monica and look forward to bringing congestion relief to the Westside."