Date of this Version
NDOR Research Project Number SPR-1(2) P544-SJ0105
The objectives of this project included a study to determine the safety effects of intersection type (unsignalized, signalized, and interchange) on Nebraska expressway intersections, quantification of the safety effects of a Collision Countermeasure System (CCS), and update of the Nebraska Department of Roads (NDOR) expressway intersection guidelines. The CCS is an Intelligent Transportation Systems (ITS) traffic control device to warn drivers of conflicting cross-traffic at rural, non-signalized intersections. The goal was that if found effective, the CCS will become part of the intersection designer’s options for expressway intersection design (other options being an interchange, traffic signals, and traffic control signs).
Analysis results indicated that exposure (measured as total entering traffic) is an important factor affecting expressway intersection safety – expected number of accidents on an intersection approach increase with increasing exposure. While the analysis did not reveal any differences in safety of unsignalized and signalized intersections, the presence of horizontal curves on intersection approaches was found to increase accidents while vertical curves placed through intersections were also found increase accidents on intersection approaches. Expressway approaches with offset left turn lanes were found safer when compared to conventional left turn lanes and expressway approaches with no exclusive left-turn lanes. The above information is recommended for addition to the existing NDOR expressway intersection guidelines to make Nebraska expressway intersections safer. This report also provides directions for future expressway safety investigative research efforts.