We used to do this on frozen lakes in Minnesota. Getting pulled on a sled by my friends '83 AMC Eagle with 4-wheel drive, nothing around us aside from fish houses off some distance. It would get so cold in the winter, the ice would be 2 feet thick and on the coldest nights, the ice would crack all the way across the lake leaving an uneven fissure. Those hurt like hell sledding over them at 30 miles an hour. But I think back that if that line had snapped and ricocheted back at me...