Funniest was probably the five lanes of rush hour traffic outside St Louis, all at a dead stop, while three cops and a woman in high heels were weaving in and out of the stationary cars, chasing after a very small dog who wasn't about to be caught. It was right out of Benny Hill.
A close second, also just outside of St Louis, but in IL, just across the the scale house on I-55, on the northbound side there was a car on fire. The local fire department came screaming up the shoulder, water hose trailing behind. When they reached the car, the hose had fallen completely off and was laying well behind them on the shoulder. The firemen jumped out of the firetruck and when they came around back, one looked to the other and said, "Where's the hose?!" And the other replied, "I thought you had it!" A Classic Three Stooges moment.
Some years ago a truck overturned on the Church Street overpass in downtown Nashville, spilling it's load of shampoo onto the Interstate below. During rush hour, during a thunderstorm.
Still, the most dangerous thing I've ever seen on the Interstate was on I-5 in Los Angeles, a little bitty Chinese woman driving a great big SUV. It doesn't get any scarier than that.