The metric is supposed to give an indication of the amount of infrastructure per resident, to augment standard persons per area measures of population density.
According to the Design Guidelines for Streets and Sidewalks, Minneapolis has 1,423 miles of roads and vehicle bridges, not counting freeways. My rough Google Earth measurement of freeways within city limits is 30.3 miles (that includes the part of 62 on the border but does not include highways 55 & 121 because I think they are in the city’s measurement, although that’s just a guess). That makes for 7,673,424 feet of streets and highways, or 20.1 feet for each of the 382,578 residents counted in the 2010 census. We’re closer to Detroit, Phoenix or San Antonio than Philadelphia, Los Angeles, or Chicago on this count.
That doesn’t seem to be an unreasonable result to me, although by measuring residents only you ignore the significant market for infrastructure represented by workers. In that case cities such as San Antonio or Houston that contain most of their employment catchment area in their city limits are going to be more accurately portrayed by this metric. One of the commenters at Mapping the Straight asked for this metric by area of paved surface – I think using lane feet would be better than centerline feet, but probably less widely available. Fun to think about anyway.