Windshield Wiper/washer problems of the 1999 Buick Regal

The nut that secures the drivers side wiper arm to the drive shaft came loose during a driving rain storm while traveling on the PA turnpike. The wipers were operating on the highest speed. The wiper arm flew off from the drive shaft and came to rest against the drivers side view mirror. Drivers vision immediately and severely impaired due to the heavy downpour and only with great difficulty and caution (negotiating through other truck/car traffic) was able to pull off to the side off the road. You would expect a nut, securing such a critical item, would be designed not to come loose. Turnpike service reattached the wiper arm and nut at no charge.