Diverging Diamond Interchange (Photo 190127801 © George Dodd | Dreamstime.com)

By Alessia Proietti

Diverging Diamond Interchange (DDI)

New interchange design proposed for Highway 12/2 near Lacombe

Feb 4, 2022 | 8:30 AM

The idea of giving Lacombe County’s Highway 12/2 interchange a face-lift with a potentially more efficient design, is beginning to toil.

Lacombe city council received a Functional Planning Study presentation at their most recent meeting on Jan. 24, put together by Stuart Richardson, Infrastructure Manager for Alberta Transportation central Region and Arthur Gordan, Project Manager for Castleglenn Consultants.

Currently, the interchange is located west of the city. Highway 2, or QE2, contains four lanes, two heading north and two heading south. Highway 12, running under Hwy. 2, contains two lanes heading eastbound, and two heading westbound.

The original Hwy. 2 was constructed in 1962 in a full cloverleaf design, with each exit lane making a full circle before intersecting with Hwy. 12. In 2010, the interchange was converted to a tight diamond configuration; its current set up.

Exhibit 1.1 of Functional Planning Study (Castleglenn Consultants)

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“The current configuration has presented a substantial safety issue for traffic, that its northbound comes off the off-ramp and then wants to go west and that intersection there without any traffic control lighting or whatnot is rather dangerous, given that the sidelines are impeded by the bridge structure itself,” said Mayor Grant Creasey.

“It has resulted in some unfortunate incidences out there that we hear about close calls quite often.”

According to the provincial Ministry of Transportation, there were 83 collisions at the Hwy. 12/2 interchange from 2014 to 2018. Approximately 60 per cent of those collisions were southbound, likely due to traffic merging onto Hwy. 2. Almost half of the collisions were either rear ends or side swipes.

The new proposed design is to convert the interchange into what is called a Diverging Diamond Interchange (DDI).

Diverging Diamond Interchange (Photo 190108189 © George Dodd | Dreamstime.com)

This new design for Hwy. 12 would begin with a traffic light added before arriving at the interchange. One side would go first, crossing over the opposing direction, inversing the lanes. In other words, the westbound road would be left (south) of the eastbound road. A tall concrete wall would be placed in between the roads so as not to confuse drivers that are now on the “other side of the road”. Once clear of the Hwy. 2 overpass, another traffic light would be installed, allowing each side to cross over again, returning back to their original sides.

Two lanes would be added to each side of the Hwy. 2 overpass, making it from a four-lane highway into an eight-lane. One lane will also be added to each side of Hwy. 12, making it a six-lane highway.

There are only two bridges of its kind in Canada. The first was built in two years, south of Calgary in 2017, at Macleod Trail and 162 Ave. South. The second was in 2018, part of the Regina Bypass in Saskatchewan.

Below is a video from the City of Calgary demonstrating how the interchange would function:

The interchange is supposed to provide a variety of benefits according to Richardson and Gordan, including smoother traffic flow, increased safety for pedestrians and cyclists who can use the empty centre in between the roads of Hwy. 12, and safer left turns as drivers will temporarily be on the left-hand side.

Some potential disadvantages, however, is the risk of wrong way maneuvers due to the changing directions, and drivers and pedestrians being unfamiliar with this type of interchange so more signage is required, and it does not allow for the construction of exit and entry ramps.

The first phase of the proposed construction is to add traffic signals and bridge maintenance within the next five years. To be completed between 2035 – 2040, the north side of Hwy. 12 would be widened first, then the south side, and two lanes would be added to Hwy. 2 making it into a six-lane highway.

The second phase of the project, to be completed between 2050 – 2060, would add two more lanes to Hwy. 2 for its final eight-lane construction, and adding two lanes to Hwy. 12 for its total six-lane construction.

The estimated cost of the project is $107.5 million.

Funding for the project is still to be determined, with the expectation for the provincial government to finance the bulk. Gordan believes one day a levy may be added to cover costs. Mayor Creasey was not in favor of the idea, stating it should be funded through regular provincial taxation.

“The whole idea of off-sighting levies is very problematic. In my opinion, it seems to penalize areas that are actively developing,” said Mayor Creasey. “I think in the short term, it’s going to drive away development along the corridor which I think is where it belongs.”

“This type of infrastructure does benefit all Albertans,” he said. “I think it’s still the most equitable route to go.”

The full proposal can be found in the Jan. 24 council meeting agenda.