The National Transportation Safety Board (NTSB) recently released recommendations to improve safety standards of tractor-trailers. In a letter to the National Highway Safety Administration (NHSA), the NTSB included research results on tractor-trailer collisions, citing both issues and ways to mitigate them. See the full letter here:

http://www.ntsb.gov/doclib/recletters/2014/H-14-001-007.pdf