To Separate or Not to Separate?: The Deerfoot Trail Case Study

Raised barriers are often provided in the median along highways. Providing a barrier can prevent severe cross-median collisions, but can also result in a significant increase in fixed-object crashes. Current guidelines for providing median barriers are based primarily on the median width and traffic volume. This paper will discuss the classic trade-off between crash frequency and severity, and illustrate it using the example of the Deerfoot Trail in Calgary, where the occurrence of several high-profile fatal crashes raised the question of the need for raised median separation. The case study will review the characteristics of median involved collisions and determine the primary contributing factors of these collisions. The current relevant standards, experience in various jurisdictions and the expected changes to the standards will be discussed. The need for a barrier will be reviewed at the case study location using both the current standards, the new standards and based on a separate review of the safety performance. The application of various barrier systems and other median modifications to optimize median operations and safety will be presented. A comparison of the various barrier systems based on the installation cost, maintenance costs, deflection, impact forces and collision performance will be provided. Using the Deerfoot Trail as an example, the multiple considerations in the determination of an appropriate barrier system for a divided highway corridor will be demonstrated.