Since Canadaian metrophlitan areas have only one--quarter the number of kilometers of superighways per capite as United States metropolitan areas---and at least as much resistance to constructing more --suburbanization of peoples and function is less extensive north of the border than south. 这句话啥意思啊,我有点不懂中间的那句插入语,请大家帮我翻意,谢谢~