So today I had my first flat out on the road, but it was on my trailer, not on one of my bikes. I use my son's Instep trailer in the folded-down position, with 1/2" plywood and plastic box attached for grocery trips. The trailer has a 100 lb. limit and I only bought $55 worth of stuff including 2 gallons of milk, but I wouldn't think that would have exceeded the limit.
I bought this trailer used 2 years ago, and I have no idea how old it actually is. The tires and tubes I'm almost certain were original. I had just left the store and was heading home when all of a sudden I started feeling a weird drag on the trailer and within a second *POW* tube blew out. Had to call my wife to come get the groceries, and fold up the trailer into her car. I rode my bike home. Couldn't fit the box in the car so I had to stash it behind a bush and come back afterwards in my car.
After I got home I pulled the tire off the rim and found a long, straight tear in the tube almost directly across from the valve stem. There is no tire puncture. I was riding about 12-13 MPH. Could it just be the age of the tube? As I said I'm sure it wasn't overloaded. I used the trailer yesterday on a ride with my son, and aired the tires up to the recommended 40 PSI shown on the side of the tires.