The influence of road design speed, posted speed limits and lane widths on speed selection: A literature synthesis

Speed is an important factor in road safety and not only affects the severity of a crash, but is also related to the risk of being involved in a crash. With the link between speed, severity and risk of a crash it has been speculated that any reduction in speed as a result of changes to geometric elements will have a positive impact on road safety. Lane and shoulder width elements play a role in driver speed choice as empirical evidence generally suggests that narrower roads, and narrower lanes on roads, lead to slower travel speeds. This lower speed selection of drivers in turn leads to lower speeds and crash rate. Drivers select the speed at which they travel as a function of a variety of driving clues and risk assessment, directly affecting the operating speed of that road. Resulting speed distributions are routinely used to justify posted speeds. Operating speeds are fundamental to the development of any roadway corridor and are used to determine appropriate roadway design elements. Roadway corridors are generally developed to maintain the tenents of cross section consistency, operating speed consistency, and driver work-load consistency. The presentation will discuss gap in the literature and provides a current and comprehensive literature synthesis on this important subject, identifying research gaps and critical research needs moving forward.