I don't mean to sound like somebody's spinster aunt, but for God's sake! You were lucky somebody didn't get killed either by your car rolling off the road and into somebody's front yard, or by some other driver ramming it.
In my varied working life I've hauled everything from grain to baled hay, scrap iron, boats, logs, and lumber. The hauler has a specific legal duty (not to say moral obligation) to see that his load stays in place. Any accident caused by a spilled load is your fault.
Also, if your insurance company can show that the load was not properly secured they can get out from under coverage of damage to the load. They can't get out from under liability for secondary damage (load spills into daycare play yard, squashing half a dozen brats). But one accident like that may very well have you paying assigned-risk insurance rates for a very long time.
End of Sermon.
seo