When you take I 5 south, turn east at Bakersfield, and take 395 south to I-15. Take that south all the way into San Diego. Just don't take I-15 at 5 am - 9 am or 1 pm to 7 pm, it will be a bit crowded.
You can check
Maps.google.com and search Riverside. Zoom out to see all the local freeways, and click on "Traffic". You can change traffic times from 'Current' to say noon on a Friday. it will give you the 'average' traffic at those times on the map. So Friday at 4 PM, it should show pretty much red lines on all the freeways that are at 15-25 MPH. I think the red/black is less than 15 MPH.
Good luck,
Fred.
