SPR 2013 Prime KTC: Transition Zone Design

The objective of this project is to provide a reference guide for developing effective roadway transition zones from high to low-speed areas. This research will provide the Cabinet with resources and decision tools for designing transition zones and selecting the appropriate range of speed reduction techniques that clearly communicate and enforce desired speeds. This research will provide guidance for a process to design transition zones and the techniques that can be used in achieving the desired speed reductions to improve safety and operations in transition areas. Rural roadways passing through a community pose a special challenge to designers. Such projects typically present a wide range of geometric and traffic operational problems, coupled with often restrictive environmental constraints. Current design approaches emphasize design speed as a surrogate for quality and safety. Furthermore, within the built-up area there are competing needs of keeping speed high to achieve mobility needs while at the same keeping speeds low to achieve perceived safety benefits. Designers often have little guidance in developing safe, high quality designs that also effectively transition the drivers from the allowed high-speed to the more appropriate speeds demanded through the built-up area. The very nature of transition zones and these types of projects require the use of flexible design and coordinated design elements. Current practices to address this issue include the use of speed limit signs and introduction of curb and gutter and have proven inadequate for alerting drivers of the need for speed reductions. The AASHTO publication “A Policy on Geometric Design of Highways and Streets” (i.e., The Green Book) does not provide specific guidance for high-speed rural to lower-speed built-up segments.