This may be an utterly boring topic to most, but typically interstate highways in the US are required to adhere to a very strict set of rules concerning lane width, curves, slope, exits; everything you can think of is supposed to be standard. I find it amusing to see such standards stretched and even broken. There are very few places where this happens, but two interesting ones are pictured below. 1) The Washington Dulles toll road is actually is an interstate within an interstate where the traffic on one highway never mingles with the other for many miles. It ensures a hassel free ride to the airport. 2) Even more radical is interstate 93 in New Hampshire's Franconia Notch where for quite some distance the interstate narrows to one lane in each direction, an almost unheard of compromise which minimizes the impact that a wide highway causes in a narrow and otherwise pristine gorge.