Accident, both parties at fault?

Accident, both parties at fault? Okay so this is what happend. I was traveling down a street and the light was green, everyone was going thru at about 45 miles per hour. Suddenly the truck in front of me decided to slam on his brakes after going about halfway thru the light turning yellow. I slammed into hi mand totaled my Expedition. He stated the reason he stopped was because there was a cop in the left hand turn lane. So in the report it states we are both at fault. Me for following to clos