In the U.S., a great deal of this research has been accomplished through partnerships between government agencies and government-supported research institutes housed at universities. Because U.S. regulation of occupational road safety is largely limited to the safety of large trucks and buses, these institutes have focused on providing the evidence base to support changes to the FMCSA safety regulations that cover these larger vehicles. Two research institutes that conduct much of the research on heavy-vehicle safety are the University of Michigan Transportation Research Institute (UMTRI) and the Virginia Tech Transportation Institute (VTTI).