Pretty sure he meant debris, not trash. Stuff that falls off trucks because it hasn't been properly secured. I've had a number of close calls due to large items blocking entire lanes on the freeways.
Roadside trash sucks, too, for different reasons.
(I call 911/CHP to report this stuff frequently, on average once a week or more. They send a CHP car or two out to road-break and remove it, or CHP+Caltrans if it's big.)