The first roundabout on SR 539, located at Ten Mile Road, began construction in March 2009 and opened on May 16, 2009, after several delays due to rainy weather. A second roundabout was opened at Pole Road (SR 544) on August 17, ahead of the Northwest Washington Fair, and was followed by a third at Wiser Lake Road in October. The final roundabout was opened on December 7 at River Road on the north side of the Nooksack River bridge. Construction on the second phase was completed in July 2010 with the installation of cable median barriers to prevent head-on and crossover collisions. Since the installation of roundabouts and cable median barriers, collisions on SR 539 have increased but injuries have declined from 96 between 2000 and 2010 to 23 between 2010 and 2018. Plans to widen the remainder of the highway to the Candian border were adopted by the county government in 2013, but remain unfunded.