Inner–outer directions

They can be used to sign individual routes that encircle a city or metropolitan area, where east–west and north–south orientations cannot be applied uniformly.

The labels are also used in select double track rail systems that form a loop, indicating the direction of travel of each line.

In 2009, Interstate 277 in Charlotte, North Carolina, became the first non-contiguous loop route to utilize inner–outer directional signage.

"Inner" and "outer" labels stem from this reasoning, applying the concept of concentric loops to the geographic characteristics of circular road or rail.

Despite the logical benefits and uniformity of inner/outer labeling, many find the concept confusing, especially those in nations where compass directions (e.g., east and west) are by far more commonly used to sign routes (e.g. the United States).

In nations that drive on the right , traffic flows clockwise in the inner lanes (blue) of a beltway and counterclockwise in the outer lanes (red).
In nations that drive on the left , traffic flows counterclockwise in the inner lanes (blue) of a beltway and clockwise in the outer lanes (red).
The Capital Beltway around Washington, D.C. , is signed by all four compass directions at various points, but is consistently signed with inner–outer labeling.
The Boulevard Périphérique around Paris, France is signed with inner and outer (French: intérieur and extérieur ) labelling. Roads in France are not given compass directions.
An "Inner Circle" train (note signage) arrives at West Street subway station on the Glasgow Subway .