Alternative Intersections and Interchanges (AIIs) are a fast-growing design solution for locations with complex operational or safety concerns. Previous research funded by NCDOT identified a new family of AII designs composed of Grade-Separated Intersections. This project implemented existing operational analysis for planning level design and alterative analysis, and developed a new planning-level safety performance estimation method.Movement-based Safety Performance Functions (MB-SPF) make up a planning-level safety analysis method that can be used to estimated project-specific crash rates at intersections.
This method estimates crashes at individual conflict points comprising an intersection as well as non-conflict point crashes and utilizes turning movement volumes rather than approach level AADT.
The methodology has showed promising results for analysis of both traditional and alternative intersection designs, but further improvements and validation of the method are needed. Suggested improvements include increased sample size, time of day analysis, effect of traffic control, bike and pedestrian data, impacts of extra travel distance, and weaving or lane change effects.
This project aims to document and consider additional factors to include in the data
collection and modeling process to further support NCDOT's estimation of planning level safety performance. This will include extensive crash and turning movement analysis to enable analysis of more facility types and design components. This research will be used to develop candidate models with bootstrapping, statistical testing, and practical analysis of the models to select the final acceptable model form. Once the final model is tested and validated, the team will develop and deliver hands-on workshops to professionals within North Carolina, to ensure consistent application of the methods.