Should we drive slower on side streets?

There is a movement afoot in the UK to reduce the speed limit on residential streets and towns to 20mph (30km/h). Statistics bear witness to a reduction in the severity of injuries sustained by pedestrians and cyclists (35% to 5%) when speeds are reduced to 20mph (30km/h). This could be a low-cost option for reducing automobile speeds instead of building speed bumps.

The reason for the change is a safer quality of life in neighbourhoods, where pedestrians, cyclists and especially children aren't in fear on their own roads. But how would Calgarians react to such a change in speed limits on side streets? I don't know how we would enforce the speeds. We can barely enforce them now.