Dark triangle shaped object moving slowly southwards with orange lights on each corner.On the way into Webster City north on Highway 17. Crossed overpass into town and noticed two bright orangish lights and a dim third making a triangle shape. It appeared to be moving slowly southward down Superior Street/Highway 17. We drove underneath it and could see against the sky that it was a perfect traingle shape dark grey or black with orange lights on either corner. It also had a lighter grey circle outline in the middle with a similar colored stripe from each light to the circle. My mother in the car noticed that the back third(from our prospective) seemed to be a bit darker, but you could still see the outline of a triangle. My father was driving and turned left to turn around back onto to the street for a better look, trees blocked the view and when we got back onto Highway 17/Superior Street you could no longer see any lights in the sky at all besides some stars. The lights were solid, and seemed to dim as we drove beneath as if they were located more on the top edge of the craft. Window was down, radio off. Couldn't hear any propeller or other type of airplane noise.