TriMet's MAX line passes through downtown Portland near the Skidmore Fountain.

TriMet’s MAX line passes through downtown Portland near the Skidmore Fountain.

Alan Sylvestre/OPB

An expansion to the Portland metro area’s light rail system is getting the green light for its route through the city of Tigard.

A 51-percent majority of voters were passing the measure with partial returns counted. The measure stems from a city charter change Tigard voters approved two years ago, which established the city’s formal position on light rail to be one of opposition unless a ballot measure of approval passed.

The proposed Southwest Corridor light rail line could reach 12 miles, making it the longest light rail line built in the region in 20 years. The northeast end would be close to where Interstate 405 goes under Portland State University. It would extend west and south to Bridgeport Village — the mall on the edge of Tualatin.

If the early results hold up and the measure passes, the $2.5 billion light rail plan will move ahead and the project developers will  proceed to the environmental review process.

Critics of the project have questioned if it will truly relieve traffic congestion along Highway 99W and Interstate 5. But supporters say light rail will give people in Portland’s southwest suburbs better access to Oregon Health and Science University, Portland Community College and Portland State University.