began the following March. Testing was extended to the re-opened downtown transit tunnel in September 2007, initially limited to weekends without bus service, and further to the Rainier Valley after the completion of the Beacon Hill tunnel in 2008. The elevated guideway in Tukwila, including crossings over major freeways and the Duwamish River, was completed in 2007 after the installation of 2,457 precast concrete segments and balanced cantilever bridges. During construction in the Rainier Valley, Sound Transit and the City of Seattle offered $50 million in mitigation funds and development opportunities to affected businesses. Construction of light rail along Martin Luther King Jr. Way South also resulted in utility lines being moved underground, improved sidewalks, street crossings, and landscaping. Opening and first extensions Central Link was opened on July 18, 2009, with a community celebration that attracted more than 92,000 riders over the first weekend of free service. Trains began operating on the segment between and stations, along with a bus shuttle to serve Sea-Tac Airport from Tukwila. The extension to SeaTac/Airport station opened on December 19, 2009, replacing the shuttle and other bus services to the airport. Sound Transit added lubrication equipment and rubber mats to segments in Tukwila and the Rainier Valley in 2010 to reduce noise levels that had reached up to 83 decibels, surpassing federal safety standards and triggering noise complaints from nearby residents. A contract dispute with the Rainier Valley construction contractor was settled in 2011, bringing the project's total price to $117 million below the $2.44 billion budget. The opening of light rail service to the Rainier Valley spurred new transit-oriented development, which had initially stalled during the Great Recession but recovered in the mid-2010s. Central Link train service was increased to a frequency of 6 minutes during peak hours, from 7.5 minutes, in 2015 to prepare for the opening of the University Link extension. The line was extended north to University of Washington station, via Capitol Hill station, on March 19, 2016, via a $1.8 billion, tunnel. The extension opened six months ahead of its scheduled date, and the opening celebrations drew 67,000 people during the first day of service. Sound Transit deployed additional three-car light rail trains to cope with higher ridership after the extension opened. The line was extended south from Sea-Tac Airport to Angle Lake station on September 24, 2016, including the opening of a 1,120-stall park and ride. The