The Detroit area is noted for having several roads named after their distance away from something. There is a Ten Mile Road and an Eight Mile Road. I believe Eminem is from the area of Eight Mile Road.
When certain units of measure are used as adjectives they are usually in the singular. So if we have a ladder that is 6 feet long, it would be a 6 foot ladder.
A man who weighs 200 pounds is a 200 pound man.
A submarine sandwich that measures 18 inches long would be an 18 inch sub.