The further through the interior you drive, the more you understand that the seldom seen constituencies which make up the fabled “heartland” to which generations of American politicians plead fealty is a quiet place. US Route 50, a century old this year, is a thin ribbon that connects Atlantic to Pacific: 3,000 miles of two-lane America running through the former Appalachian mining towns, through prairie towns and across the more remote sections of the Nevada desert. If nothing like as lauded as Route 66, also 100 years old this year, “50” has modelled itself as the ‘backbone of America’, leaving...