Immediately after it opened, a report commissioned by Metro found that, while the number of hours per day when peak traffic conditions existed had declined, rush hour commute times on the freeway were up compared to 2009—prior to the start of construction.
People who hate spending money to widen highways love to talk about "induced demand" which is how those improvements just bring more cars onto the highway as people switch to highway travel.
But it's actually worse than that. People don't just switch to highway travel from other roads and modes, they switch their travel times. And because congestion is an externality they do it in particularly infuriating - for everybody else - ways. You get more cars on the road all day, and you especially get more cars at rush hour. So, yes, widening highways can, actually, make your rush hour commute worse.