Caltrans is beginning to build a new westbound connector, but has to demolish the old one first.
Starting Wednesday, drivers using the ramp connecting southbound 101 to eastbound 580 must merge into just one lane.
On Sunday, the westbound 580 to northbound 101 overpass will close completely and all traffic will have to share the eastbound connector ramp.
The new connector ramp will improve traffic flow with two lanes and two shoulders.
During construction, Caltrans says drivers will experience delays of 10-30 minutes.
"For about seven months, you're going to be down to just one lane in each direction, so that does cut capacity by 50 percent, so we are expecting a return to the congestion we saw before," Caltrans spokesperson Bob Haus said.
The original connector ramp first opened in 1956. Congestion has gotten worse since then, prompting the plan for this replacement structure.
Construction should be finished by October.