The project wasn't supposed to be finished until late summer at the soonest. But weather helped ramp up the schedule.
The underpass is expected to relieve congestion on Yakima Avenue, as well as help emergency vehicles get to a scene faster.
Before opening, there was a ribbon cutting ceremony and a caravan of city vehicles had the opportunity to drive the new road first.
"This area has had about four years of continuous construction and now it's come to an end and finally the businesses along here and they'll have their better access and they're happy about it," said Yakima Spokesperson Randy Beehler.
The last bit of construction will be a walking path on the Lincoln Avenue Underpass next year.