The nearly $6 million project was paid for with federal and county money. Features include a pair of 12-foot travel lanes, an 11-foot truck climbing lane and eight-foot paved shoulders for bicyclists and pedestrians.
Engineers said the new Tieton grade will help improve safety.
"It will certainly make it easier for accidents to be avoided," said Yakima County Engineer Gary Ekstedt.
Crews will finish up pavement striping and installing guard rails this week. Two lanes of traffic will be open until work is done.
It should fully be open the middle of next week.