Abstract Manager

There is increasing interest from jurisdictions to include road safety considerations when planning interchanges. Both The City of Calgary and Alberta Transportation and Economic Corridors (TEC) require the project team to consider and evaluate multiple interchange types during the functional planning study (FPS) process then score each option using predetermined criteria.  Safety for both vehicles and vulnerable users was one of the evaluation criteria considered in two recent FPS completed by ISL.

Predicting safety performance for a future interchange is challenging. Safety performance functions (SPFs) and collision modification factors (CMFs) are not well suited to use for interchange planning studies, especially if the crossroad does not currently exist. Furthermore, there are few if any SPFs for pedestrian collisions due to generally small sample sizes. To overcome these challenges, ISL incorporated multiple methods for evaluating safety of both vehicles and vulnerable users for multiple interchanges during the evaluation process. The methods of safety evaluation include:

• A planning tool developed by the US Federal Highway Administration (FHWA) for estimating expected collision frequency
• Number of conflict points and proportion of high-speed conflicts for each interchange type
• TEC's benefit cost analysis tool - which includes a safety component
• Combining the expected collision frequenct with TEC's benefit cost analysis tool

While none of the above methods of evaluation are perfect, using multiple methods allowed safety to be a consideration during the options evaluation phase of functional planning. The presentation will elaborate on each evaluation method and their limitations and how it affected the overall selection process on one recent interchange FPS completed by ISL.