My tyres are beginning to get worn. Does this mean that they are unsafe?

Question from visitor, 18/12/2009 :My tyres are beginning to get worn. Does this mean that they are unsafe?
Answer by rezulteo, 18/12/2009 :

On wet roads braking distances are 3 times longer than on dry roads. On wet roads, a vehicle with worn tyres will have a braking distance that is even longer, including an increased risk of aquaplaning.