About the research
Iowa has a long history of converting two-lane and four-lane roadways to a three-lane cross section consisting of a through lane in each direction of travel and a center two-way left turn lane (TWLTL) for safety purposes. Several notable studies were conducted in Iowa in the early 2000s demonstrating the safety effectiveness of such conversions as well as offering guidance for conversion. These studies also suggested possible greater safety impacts compared to other contemporary studies.
Several different roadway and roadside characteristics may impact the possible effectiveness of three-lane cross sections. Some of these characteristics are collected and maintained by the Iowa Department of Transportation (DOT) through the Roadway Asset Management System (RAMS) (and formerly Geographic Information Management System [GIMS]). However, accuracy issues have been found to exist with some of these characteristics, including the presence of a TWLTL, due to the frequency of update and reliance on agency reporting. Additionally, several other characteristics that may potentially impact safety and/or operations have not been traditionally inventoried.
The primary objectives of this project are to identify three-lane roadways throughout the State of Iowa and collect (or update) pertinent roadway and roadside characteristics. Emphasis will be on current characteristics but may extend to historic characteristics, where available. Furthermore, relevant crash experience along the identified three-lane roadways will be captured for future safety analysis. Documenting the history and characteristics of three-lane sections will facilitate evaluation of the safety and/or operational-related impacts of these roadways. It will also allow for identification of common characteristics of well-performing, existing sites and similarities between them and potential three-lane conversion sites.