The objective of this report is to identify known relationships between commercial vehicle safety and crash causation factors and to prepare a synthesis of safety implications of oversize/overweight (OS/OW) commercial vehicles. This information can be used to support commercial vehicle enforcement and permitting practices and justify expenditures and investments on size and weight enforcement to enhance safety. In producing this report, insight was gained into the impacts of truck size and weight (TSW) regulations through three case studies. The state of practice in estimating large truck crash rates is complicated because of the many configurations and the wide range of possible weights for any particular configuration. This report highlights four primary findings regarding the contributions of OS/OW to commercial vehicle crashes found by its researchers.