Problem 25 (2014 AMC 8)

A straight one-mile stretch of highway, $40$ feet wide, is closed. Robert rides his bike on a path composed of semicircles as shown. If he rides at $5$ miles per hour, how many hours will it take to cover the one-mile stretch? [See figure in original PDF] Note: $1 \text{ mile} = 5280 \text{ feet}$