Adding salt to water lowers the freezing point, thus preventing the formation of ice.

The simple answer is that salt dissolves into the frozen water and lowers the freezing point. Normally water freezes at 32 degrees fahrenheit, add salt and it will take a lower temperature to freeze that water.

Full scientific explanation:
http://tinyurl.com/2fxvp

http://tinyurl.com/37mula

http://tinyurl.com/2wfdqh (Reuters)

consumer reports
http://www.consumerreports.org/cro/index.htm

Here's the list of cars:
http://tinyurl.com/2jjg8p

Sorry, that's all I could find.