This project involves the analysis and design of a partial Displaced-Left-Turn (DLT) intersection to address road safety and operational concerns at the St. Peters Road intersection on the Trans-Canada Highway in Charlottetown, PEI. As part of this work, PEI Department of Transportation, Infrastructure and Energy analysed numerous intersection improvement and grade separation alternatives, and concluded that an innovative intersection design was necessary.
Although promoted by the FHWA, used by several State DOT’s, and recognized in the 2017 TAC Geometric Design Guide for its operational and safety benefits, the application of this innovative configuration is new to Canada.
In addition to the significant traffic operational improvements resulting from implementing the DLT, safety benefits will also be realized. When compared to a conventional intersection, using the partial DLT reduces conflict points from 32 to 30. This is a reduction of 2 crossing conflicts typically associated with increased collision severity. Pedestrian-vehicle conflicts are also reduced from 24 to 20. Results from before-after studies in the US suggest a 24% reduction in total crashes and a 19% reduction in fatal and injury crashes following installation of the partial DLT.
As the DTL is new to Canada, a cautious approach to the analysis and design was taken. This approach included the application of several analytical methods and tools to assess traffic operations and careful consideration of safety through the use of a senior advisory panel consisting of road safety, human factors and innovative designer experts.
Various DTL intersection design configurations were also observed in operation under a variety of environmental and traffic conditions, and interviews with representatives from several State DOT’s were conducted to glean information for the development of best practices and design elements for application in the Canadian context.
This project is an excellent example of the application of innovative design solutions to address complex design challenges. It provides a valuable suite of Canadian geometric design, signal, signage, and positive guidance best practices for inclusion in future DLT intersection designs in Canada. In addition, it provides valuable insight on a public education program for the introduction of this new intersection configuration.