Sound Transit construction crews Wednesday completed the first span of elevated light rail guideway in Tukwila. The milestone marks the launch of a nearly 380-foot-long steel truss that will take a five-mile journey through Tukwila, leaving a light rail guideway in its path.

Over the last several months people have watched with anticipation as concrete piers up to 65 feet in height have sprouted up along State Route 518 between Interstate 5 and the airport exit. Between now and 2007 the truss will “walk” from pier to pier along the five-mile Tukwila alignment, hoisting into place the pre-cast concrete segments that will form most of its elevated guideway.

On Wednesday, crews used the truss to hoist into position the final pieces of the first span. A typical 120-foot span between two columns is formed by 12 pre-cast concrete segments. The truss lifts the segments into place one by one and supports them while they are connected. The truss then moves forward to the next column. The Tukwila alignment includes almost 200 spans. The work is being performed by PCL Construction Services, Inc., a respected Bellevue-based firm.

Construction of the Central Link light rail system began in late 2003 and currently is about one-third complete, with rapid progress occurring all the way from downtown Seattle to Tukwila. Overall, construction bids came in 6 percent below estimates and construction is currently about $200 million under budget. Sound Transit remains on schedule to begin carrying passengers starting in mid-2009. The airport light rail connection — Airport Link — is scheduled to be completed by December 2009. By 2020 the system is projected to carry more than 45,000 riders daily between downtown Seattle and the airport.