This report contains the findings of research performed to quantify the safety and operational impacts of design element trade-offs and their associated risks. The report details the research performed and includes specific recommended crash prediction models and Accident Modification Factors (AMFs) for shoulder width and median width on rural four-lane roads.

This comprehensive 2nd edition covers the key issues that relate human behavior to traffic safety. In particular it covers the increasing roles that pedestrians and cyclists have in the traffic system; the role of infotainment in driver distraction; and the increasing role of driver assistance systems in changing the driver-vehicle interaction.

RB’s National Cooperative Highway Research Program (NCHRP) Synthesis 432: Recent Roadway Geometric Design Research for Improved Safety and Operations reviews and summarizes roadway geometric design literature completed and published from 2001 through early 2011, particularly research that identified impacts on safety and operations.