Quote:
Originally Posted by Frequitude
Love the road planning nerdery. Always kind of wanted to take a course in in university.
So would the optimal intersection of two perpendicular roads from a traffic flow perspective and ignoring costs be 4 of those big looping ramps for left turns?
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A stack is the theoretically perfect interchange.
Flyovers could be 2 or more lanes for more capacity if required. Canada has only 1 true stack, in Toronto. Aside from cost, people don't like these because the top level flyovers have to be 25 meters up and it's pretty unsightly, and you just need a ton of land.
If you have unlimited land, you can just swing all the flyovers way out to the side and never need to reach 4 levels, this is sometimes called a "turbine". Here at Stoney/Deerfoot in the NE, you can visualize that if the flyovers went right over the center of the interchange it would be 4 levels, but land is generally plentiful here so there's no need to do it as dirt for embankments is cheaper/easier/safer than 200 meter long monster bridges.
Anthony Henday Drive/Yellowhead Trail in Edmonton is the only interchange in Alberta where two ramps are truly 3rd level, and it's only because there's train tracks and refineries in the way preventing AB Trans' usual style. It's just really expensive.
Anthony Henday Drive at Yellowhead Trail, Edmonton by
Acey, on Flickr
You can really see how much of a dump Edmonton is from the top level. It's about 20 meters up.