Jet streams are high-elevation "rivers" of air that travel between 120 and 240 kilometers (75 and 150 miles) per hour in a west-to-east direction, basically, it is a type of wind that is in the upper part of the troposphere or in the lower stratosphere, commercial aviation takes advantage of jet streams to travel long distances as they significantly reduce the journey's duration and also fuel consumption. It is like an air highway. That is why flights from North America to Europe last less than those from the opposite direction.