Typically an entire railroad system (the lines of a railroad or a related group of railroads) will describe all of its lines by only two directions, either "east and west", or "north and south". This greatly reduces the possibility of misunderstanding the direction in which a train is travelling as it traverses lines which may twist and turn or even reverse direction for a distance. These directions also have significance in resolving conflicts between trains running in opposite directions. For example, many railroads specify that trains of equal class running to the east are "superior" to those running west. This means that, if two trains are approaching a passing siding on a single-track line, the "inferior" westbound train must "take the siding" and wait there for the "superior" eastbound train to pass.