I didn't use the word "horrendous". However, let's use the 2016 population of Okotoks (approx 29,000). Let's further assume a little over 1/4 of them drive to Calgary daily.
Now examine the traffic on Deerfoot - average daily traffic was 168,000 vehicles calculated at the midpoint in 2016 (entering downtown at Memorial).
https://en.wikipedia.org/wiki/Deerfoot_Trailhttp://
"Average daily traffic" is defined as "
Average daily traffic or
ADT, and sometimes also
mean daily traffic, is the average number of
vehicles two-way passing a specific point in a 24-hour period, normally measured throughout a year."
https://en.wikipedia.org/wiki/Annual..._daily_traffic
What this means, is that 168,000 "passing a specific point" is the same vehicle is counted twice on a given day. So divide that number by 2 to calculate the average number of vehicle trips a day on Deerfoot (84,000).
As it is the midpoint, the 84,000 figure again needs to be divided by 2 to reflect traffic in from each end of the city (42,000).
Lets assume only 8,000 people drive in from Okotoks a day. That's almost 20% of the traffic on the southern half of Deerfoot per day hitting the 2-lane overpass at Glenmore. And that's assuming every Calgarian enters before the Glenmore overpass (everyone from Okotoks does).
So yeah, I guess you're right. It seems that deadbeat town does have a horrendous effect on traffic in Calgary.