Afully loaded tractor-trailer traveling 55 mph could take up to to come to a complete stop:

Answer;
A fully loaded tractor-trailer travelling 55 mph could take up to 400 feet to come to a complete stop. 

Explanation; 
Tractor trailers take longer to stop than a car traveling at the same speed.
The average passenger car traveling at 55 mph can stop in about 130-140 feet, less than half the length of a football field.
A fully-loaded tractor-trailer may take more than 400 feet to come to a complete stop, or one-third more than the length of a football field.