National parks you have Noise and scenery. Apparently car noise is a significant issue for animals. Then you have the people who are just pulling off randomly or veer out of lanes because they are looking at the mountains.
I don’t think 90 is reasonable but the stretch from Canmore to Lake Louise should be lower than the rest of the highway as risks are different.
BC had a policy to set roads based on design speeds and 80th percentile speeds and adjusted a bunch of speed limits. They also found a significant increase in deaths.
https://www.cbc.ca/amp/1.4857985