His point is fair though; just replace "road" with "railroad".
Canada's rural roads (read: most of Canada's roads) are already mostly two-lane.
Most roads are not four-lane ones. Think residential roads, for example.
Over time, most cost of a road is maintenance cost, not initial construction. While this probably isn't linear with use, it does scale with use, so that lower use means lower maintenance cost. The cost of a single lane road supporting current usage levels is not an individual less quantum unit of road cost.