That doesn't say anything about the cost of sidewalk relative to the cost of building a road. And that's retail prices, specced out by square footage. When you're building sidewalks at the scale of entire cities it's definitely cheaper.
You need to find a source that shows what the cost to the government is per mile of road versus mile of sidewalk. You can't compare retail prices of sidewalk that would be charged to homeowners to what the government is paying to build a road.
