Wheel Bolts problems of the 1996 Chevrolet Cavalier

Approx. 1 month ago, the car began to "knock" and shake very badly. I drove it to a repair shop near my home, where it was diagnosed with 5 broken bolts in the front driver's side wheel. This was fixed. Yesterday (7/24/02), at approx. 12:00 noon, I was driving with my children northbound on route 18 in east brunswick, NJ, when the car began to knock and shake again, and my front passenger side wheel just fell off. Luckily, due to traffic conditions, I was in the right lane and not travelling very fast (@ 20-25 mph). Luckily, I was right at the entrance to a mobil station when it happened, and the wheel rolled into their parking lot; I found the pieces of the bolts that were broken all around the parking lot. The wheel caused a small amount of damage to the back of a car (a backup sensor was broken) that was in the lot. This damage was around $200; the cost to put my wheel back on, and for all new bolts on that wheel was about $100. There is also damage to my passenger side fender, for which I have not gotten an estimate for, my husband is guessing about $700; could I furnish you with an exact estimate at a later date? additionally, upon puttingthe wheel back on, they discovered damage to the "u-joint". We transfered the car to our own mechanic to have this problem addressed; I will have more receipts, probably tomorrow. I am also having the mechanic replace the bolts and lugnuts on both rear wheels - I strongly feel that there must be something wrong with these bolts for them to keep breaking like this.