A couple of years ago the government of Manitoba announced that it was going to upgrade the South Perimeter Highway.
Work has begun. This whole summer equipment has been digging and plowing and getting land ready for new split-grade intersections at the St. Anne’s Rd. and St. Mary’s Rd crossings of the Perimeter. Yes!! It’s finally happening.
But *WHAT* is actually happening? I did not realize how elaborate the St. Mary’s interchange was until I saw a diagram on Facebook in the South Royalwood Group run by ex-blogger and SOS alumni David Watson. It’s not just an overpass — it’s an overpass with TWO roundabouts!
What is a diverging diamond interchange? It’s where one road (the Perimeter Highway in this case) continues uninterrupted, and the other (St. Mary’s Rd.) is divided, and each direction crosses over the other such that you’re driving on the opposite side that you normally would, UK-style, as you pass over top of the other road. Confused? A diagram will help:
The advantage is that you never have to turn left across traffic. A disadvantage is that traffic is disrupted by controlled intersections … four of them in this design. Another is that it’s somewhat confusing. People will learn, but it is a clumsy design in this blogger’s opinion.
Thankfully, sometime between June and July, 2020, someone at the Department of Transportation and Infrastructure came to their senses and scrapped this mess for the roundabout solution.
The fact that the diverging diamond design is still posted on the project web site as an Ultimate Stage Design Drawing is confusing, but they do state quite clearly that the roundabout solution is the one that they’re going with. At least for now: every intersection upgrade has a ‘phase 2’ where lanes are added and other changes are made to accommodate yet more traffic. In the case of St. Mary’s Rd this would mean replacing the roundabouts with two additional overpasses. A three overpass intersection. We’ll see about that …
I know some people are opposed to the whole South Perimeter Project. It is, no doubt, expensive, but some people are also opposed to overpasses and freeways conceptually. I think it’s a long overdue project. Here’s why:
- Safety. High volumes of highway-speed traffic interacting at grade is not conducive to safe driving. Accidents are not terribly common, thankfully, but when they do happen they can make the news. Related: new active transportation paths will be built into most intersection upgrades, including St. Mary’s Rd., allowing cyclists and pedestrians to cross the Perimeter Highway without crossing the highway.
- Efficiency. Traffic volumes have doubled in the last 20 years. Slowing down, stopping, idling and getting back up to speed takes time and resources. Thousand of cars and trucks doing that every hour adds up to a big cumulative impact on productivity.
- Environment. All of the above things also add up to a large environmental footprint. Cars and trucks are far more fuel efficient when they’re travelling a constant speed.
- Urbanization. Yes really. Freeways have been known to destroy urban environments, but a free-flowing Perimeter would help keep cars and especially trucks out of the city. Look at a map of Barcelona, or any other walkable urban city. Freeways outside | urban inside.
- If Regina can do it so can we!