Anyone who’s baked a loaf of bread knows that heat and time activate yeast, causing dough to rise. Perhaps if a truck driver in Tacoma, Washington, had known this, his trip last week could have been a bit less messy. Last Monday, July 24, the driver noticed his cargo—giant plastic trash bags full of bread dough—was overflowing onto the highway. Unusually heavy traffic made the truck driver’s journey longer than usual, and the bags of dough sat in the the coverless, unrefrigerated truck exposed to 80ºF weather. Eventually the dough began to rise uncontrollably. 

If you’ve ever wondered why some baked goods recipes recommend letting dough rise overnight in the refrigerator instead of leaving it out on your warm kitchen counter, this is why.  

“Just when you think you’ve seen it all, you’ve got dough on the freeway,” Washington state trooper Brooke Bova said in a Twitter livestream. Stopping to assist during the incident, Bova explained to the Washington Post that the driver was making a routine trip to haul leftover bread dough from a nearby bakery to a plant where it’s turned into livestock feed. He wasn’t expecting traffic, and the extra time combined with the sun beating down on the dough caused it to burst from its plastic bags and ooze out of the truck and onto the highway. Although the driver had been making this journey for years, nothing like this had ever happened before, so he drove for miles before noticing the problem.

Bova told the Post that a number of other drivers on the road reported a truck spilling what appeared to be foam or insulation, and she had to check it out for herself.

The dough was cleared quickly from the highway, and no one was injured.