Row of trucks across I-5 in San Diego?

Back in October of 2011, early on a Saturday morning (I think...), I got onto the I-5 headed southbound just south of the 56 (north of San Diego). I quickly noticed that there was no one on the freeway around me. I looked in my rear-view mirror and saw that ALL 5 lanes of traffic, about a half-mile behind me, were being blocked by slow-moving 18-wheelers all lined up next to each other. I could see a bunch of traffic backed up behind them. It was so bizarre and I've always wondered what it was all about...

Does anyone on here have any idea what was going on that morning or has anyone heard of anything similar happening elsewhere? Maybe some kind of memorial service or protest?

I apologize if this has already come up elsewhere on this forum but I couldn't find anything describing this occurrence.

Thanks in advance!