Trucks are one of the greatest hazards for bicyclists and pedestrians. The problem not just the poor visibility, but also the lack of protection around the wheels. Sideguards would greatly reduce that vulnerability, by deflecting bikes and peds away from the truck in a collision. Most trucks in Europe and Japan are required to have sideguards, but no such regulation exists in the United States.
In April 2014, the NTSB issued a recommendation for sideguard regulation. The NTSB is only an advisory body, however, so any regulation must be implemented by the NHTSA. On July 10, 2014, the NHTSA published its response to the NTSB recommendation:
NHTSA is planning on issuing two separate notices—an advanced notice of proposed rulemaking pertaining to rear impact guards and other safety strategies for single unit trucks, and a notice of proposed rulemaking focusing on rear impact guards on trailers and semitrailers. NHTSA is still evaluating the Petitioners’ request to improve side guards and front override guards and will issue a separate decision on those aspects of the petition at a later date.
When the NHTSA says it needs more time to study a problem, it usually means the agency will not take action. In this case, I would be happy to be proven wrong, but it does not appear that the NHTSA is interested in the safety of bicyclists and pedestrians.
Systemic Failure 
Out of curiosity, would the streamlining wind-deflector pieces that are fitted to some modern trailers serve this same purpose? If so, the trucking companies would come out ahead in fuel savings, while also being safer.
On the plus side, Boston just passed a policy requiring them on municipal vehicles.