It was positive, Calgary has free parking after six pm so it gave people the perceived availability of parking. Also, when the street is active the speed of the cars probably doesn't top 30 km/h. The street only has one lane open to one way traffic, and is paved in concrete pressed to look like stone so that the street feels different to drivers to act as a mental deterrent to excessive speed.
This excerpt from a Calgary Herald article can fill in some blanks:
After the Stephen Avenue Mall was first instituted as an exclusive "pedestrian corridor" along 8th Avenue, it quickly became a no-man's land of closed retail stores, questionable and undesirable street activity, as well as a highly unsafe environment, particularly at night. In the late 1980s, I was a member of the Calgary planning commission. I had the temerity then to suggest that a great variety of European examples indicated that control of traffic at certain times of the day, coupled with full vehicular access at other times, provided retail exposure and related viability, as well as an enhanced level of personal comfort and security through more "eyes on the street" passing through. All this, while also maintaining a great opportunity for strolling when the pedestrian density needed that.
At the time, I was castigated for suggesting an idea that was not consistent with the intent of the downtown plan's call for a "pedestrian mall." Fortunately, somewhere along the way traffic did get remixed into the arrangement and the mall has become a successful people place. The key point of this example is that sometimes well-intentioned policies don't work very well, and benefit from rethinking and more balanced solutions.
The mall was switched over from full pedestrian mall to the hybrid european model in either 1989 or 1990. To show how bad a place Calgary's downtown was then, Mayor Klein's main defence for keeping cars off of 8th was to make sure prostitution did not return to the main strip.
Ald. Duerr who later became Mayor was the champion of the hybrid pedestrian mall.
But Klein said the new festival market, Barclay Mall, Chinatown and new projects under construction will help attract people downtown - not traffic on the mall.
"You want to create an environment where people can walk around and sit down, and have a coffee and have a beer. The last thing we need is cars with exhaust fumes, cigarette butts and all the other things associated with traffic."
Klein said there's a risk the the introduction of traffic could lead to prostitution.
"It will provide an opportunity for activities related to motorvehicle solicitation," he said.
The plan called for one westbound lane of vehicular traffic between 6 p.m. and 6 a.m., sidewalk cafes, a 1912 heritage theme and a central square
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I think the lessons from Calgary beyond the obvious ones up above are that you should start with a small strip and as it becomes successful you can expand it. Also, it is more important to have it in your central business district than on a currently successful retail strip (even if Europe tells us that already).