In a study of 5 years of claims processed,  18.9%  of all losses were front end impacts and  22.7% were rear end impacts. Interestingly enough, the front end average appraisal severity was $3439 while the rear impacts came in at $2050.  The chance of a left front or right front impact was 10.2% on both the right and the left sides.

Source: 2010 AutoClaims Direct, DirectLink .