Why does my 1993 cavalier overheat at stoplights but not on the highway?

Most likely your radiator fan is not spinning when stopped. When the car is moving the airflow generated is cooling your car. As a first step, open the hood, start the engine, then turn on the air conditioner. This should energize the cooling fan(s). If the fan does not turn on, have someone detach the wires and give the fan 12 volts. If the fan works with the 12 volt power source applied, then it could be a fan switch, fan switch relay, fuse, or fusible link. I hope this help, John