2004 Toyota Prius. 300K+ miles.
Car is not with me at the moment. I’m still trying to get more info. Family member was driving it.
Based on this visual, what would cause this type of a blowout?
Wear/age of tire? Overinflation? Underinflation? Hitting something on the road? A slashed tire, either intentional or unintentional?
TMK, the tires were fine last time I took it to Costco.
That’s called tire went flat and they kept driving (intentionally or not maybe just couldn’t get over right away) but that’s usually the culprit to a shredded sidewall like that
That’s probably it!!!
Family member was driving it
These kinds of things always happen when family members / friends drive the car...
looks like either hitting a big bump, or possibly a blow out due to dry aging of the rubber....
(Although last time I had extremely dried aged tires (a pair of no-name Ford OEM ones, and Toyota OEM from General Tire) - both leaked air way before appearing close to blowing out)
Inspect if any of the other tires if it has anything like these... (Although this is a very extreme example)

Wear/age of tire? Overinflation? Underinflation? Hitting something on the road? A slashed tire, either intentional or unintentional?
Any of the above.
What did the family-member tell you???
Hope she/he was looking at the road when driving and so can contribute (big hole, big block of concrete a.s.o.)
When not, you might be tempted to crumble their driving-license.
BTW: how do the other 3 tires look?
1 tire looks amazing. It’s practically brand new. The other two look decent but aged.
Family member just said they heard something funny, and thought it was the trunk beside them. But when the truck passed, realized it was them. Didn’t run over anything that they know of.
When the truck has been a dump truck and aside of your car on the side of the blown tire, I could imagine it lost some sharp items in passing..
There was no shooting involved??
Good they could stop the car without more/personal damage!
That’s probably it!!!
I thought that part was obvious. I thought you were asking what caused the tire to lose air.
Family member just said they heard something funny,
something funny like the sound of a flat tire getting shredded?
@mmj "something funny like the sound of a flat tire getting shredded?" {blackemo}:laughtertotears:
Yup. They didn’t realize what it was though. Sounded like it was coming from the truck next to them.
@Kaizen The family member was OK tho, right? Hope so. You can always get another tire... As a 13y/o boy, started working in shop of dad's Goodyear Store... saw many crazy tire "events" and had a few of my own by 18.
@mmj 's response reminded of a tale I tried to pass off on my dad only he called me out on it.. still remember "that look" he gave me, "Yeah... sure" is the polite terminology!
Everyone is okay. Thank you!