Calgary – Ribbon Cut on Canada’s First Diverging Diamond Interchange

After two years of construction, the long-awaited diverging diamond interchange (DDI) at Macleod Trail and 162 Avenue in south Calgary opened on time and on budget, addressing one of The City's most persistent bottlenecks.

Chris Delanoy, Director and Project Manager at ISL Engineering and Land Services (ISL) says: “This was a challenging location. Land had been reserved here decades ago for a partial cloverleaf interchange but it did not stand the test of time and we needed new thinking. We had evaluated DDIs at a number of locations in Calgary before but it was never the right fit until 162 Avenue. The DDI provides a safe, high capacity, long-term solution that was constructed with minimal traffic disruption and no property impacts.

The DDI idea originated with and was championed by David Breu, Manager of Transportation Design in ISL’s Calgary office. Dave recalls: “We were very conscious throughout the design phase of the responsibility that we were carrying in implementing the first DDI in Canada. We thoroughly surveyed current practices in DDI implementation in the United States and paid careful attention to getting every detail right for Calgary’s unique context including driver behaviour and climatic conditions.

Chris added, “this major milestone was achieved because of the close collaboration between ISL, The City of Calgary and Graham Infrastructure. The City and their senior leadership team in particular were instrumental, providing expertise across many departments and motivating the team by providing strong support to successfully implement this new and innovative solution.

A historic event, the decision to build the first DDI in Canada was made for a variety of reasons including increased safety and capacity, and ease of construction. The design promotes a free flow of traffic both below and above the new overpass. Unlike a standard diamond interchange, traffic is divided based on direction – all left-hand traffic is funneled to the left side of the road and can turn onto the major thoroughfare without waiting at a stop light or worrying about crossing oncoming traffic. The construction sequencing even allowed for the project to remove the traffic signal from Macleod Trail in October 2016, tremendously improving traffic flows nearly a year before the interchange was finished.

Based on statistics out of the USA where DDIs are more commonplace, The City of Calgary can expect as much as a 40 per cent reduction in overall crashes and a 75 per cent reduction in turning movement crashes.

The City also estimates that delays going east-west will be cut in half from what they would normally be in a standard diamond interchange where a bottleneck can add as much as 20 minutes to a commute.

Despite the ribbon cutting in August, parts of the roadway will still be under construction into September with expected completion by October 2017.

To learn more about the project, watch the videos at the National Post and the CBC

If you are thinking about implementing a DDI in your jurisdiction, ISL would be pleased to lend our expertise and share lessons learned from this first-in-Canada application. Please contact David Breu at This email address is being protected from spambots. You need JavaScript enabled to view it.

August 2017

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