One car was westbound on U.S. 18/151 when it veered into the median, overturned and landed on an eastbound car, sheriff's officials said.
Dane County Coroner John Stanley said the crash killed 48-year-old driver Janet Indermuehle, her 15-year-old son Daniel J. Hall, and 14-year-old passenger Tiffany Marie Kastner. All three were from Potosi, Wis.
The driver of the second car was injured and taken by medical helicopter to University Hospital. No one else was in the second vehicle.
The crash happened about 4 p.m. Wednesday just east of Mount Horeb.

