Flying junction

Trains use special paths to move.

Sometimes tracks must cross. One track can go over another. This uses a bridge.

This is called a flying junction. It helps trains pass safely. No train has to stop for the other. This keeps the trains moving fast.

Tracks can also go under. This is like a tunnel. It also helps trains avoid each other.

Many lands use these paths. They are in places like France and Japan. They are also in the USA. These paths keep travel smooth.

Trains often need to change paths. Sometimes, two tracks must cross each other. At a normal crossing, trains might have to wait. This is called a level junction. To avoid waiting, engineers build a flying junction.

In a flying junction, tracks do not touch. One track might go over the other on a bridge. This is also called a flyover. Another way is to go under. This is called a dive-under or a burrowing junction.

These paths help trains move without hitting or blocking each other.

High-speed trains use these junctions a lot. In France, the TGV trains use them to stay fast. There are special parts called switches that help them turn.

These switches let trains turn at high speeds. In Japan, the Shinkansen trains also use them. A new one is being built at Fukushima Station. It should open in 2026. Many countries use these paths. You can find them in the USA, the UK, and many other places.

Trains often need to change paths as they travel. Sometimes, two different tracks must cross each other's way. At a normal crossing, called a level junction, tracks meet at the same height. This can cause problems because trains might have to wait for others to pass. To solve this, engineers build a flying junction.

This special setup allows tracks to cross without touching. It is also known by the technical name grade-separated junction.

There are two main ways to make a flying junction work. In a flyover, one track goes over another using a bridge. If the tracks go the other way, it is called a dive-under or a burrowing junction. These paths allow trains to move in different directions at the same time. Some junctions are very simple with just one track passing over another. Other junctions are much more complex and allow many different routes. These look like large highway interchanges where many roads meet and split.

High-speed trains rely on these junctions to stay fast. On the French TGV network, most junctions are grade-separated. For example, the junction at Pasilly and the one at Courtalain use special switches. These switches, also called points, let trains turn without slowing down too much. The TGV network even has four high-speed triangles. These are named Fretin, Coubert, Claye-Souilly, and Angles.

These shapes help trains move between cities like Paris and London smoothly.

Many different countries use these clever railway designs. In Japan, the Shinkansen high-speed trains use them near Omiya and Takasaki stations. A new flyover junction is being built at Fukushima Station. This new part of the track should open in 2026. The Netherlands also uses many flying junctions, with between 25 and 40 found across the country. In the United States, you can find them in big cities like Chicago and Boston. Even the New York City Subway uses them to keep trains moving.

Flying junctions help our world stay connected and moving. Without them, many train lines would get stuck waiting for each other. You might see a bridge carrying a train high above the ground. Or you might see a track disappearing into a tunnel to go underneath.

These structures make sure that passengers can reach their destinations on time. They turn a messy crossing into a smooth and organized path for travel.

A flying junction is a specialized railway arrangement designed to manage intersecting tracks. In a standard railway setup, tracks might meet at a single level. This is known as a level junction or a flat junction. At these points, trains traveling on different routes must cross at the same grade. This creates a conflict because one train must wait for another to pass before it can move. To prevent these delays, engineers use grade-separated junctions.

This method allows tracks to cross without physically intersecting on the same plane.

There are two primary ways to achieve grade separation in a railway system. The first method is a flyover. In a flyover, one or more tracks rise above the others using a bridge. This allows a diverging or converging track to pass over the main line safely. The second method is a burrowing junction, often called a dive-under. In this setup, the diverging line passes below the main line.

Both methods ensure that different train movements do not block one another. The complexity of these junctions can vary greatly. A simple junction might involve only a single track passing over another. More complex versions resemble highway stack interchanges, allowing many different routings simultaneously.

High-speed rail networks rely heavily on these advanced structures to maintain velocity. On the French Lignes à Grande Vitesse (TGV) network, nearly all junctions are grade-separated. At specific locations like Pasilly and Courtalain, the junctions use specialized high-speed switches. These switches, also known as points, allow trains to transition between lines efficiently. While the main line maintains its normal speed, these switches permit a diverging speed of 230 km/h.

The French LGV network features four major grade-separated high-speed triangles. These are located at Fretin, Coubert, Claye-Souilly, and Angles. A fifth location, Vémars, is almost entirely grade-separated, except for a single-track link connecting Paris Gare du Nord to Paris CDG airport.

Japan also utilizes grade-separated junctions for its Shinkansen high-speed trains. Although the Shinkansen network covers a vast area, there are only two such flyover junctions under JR East jurisdiction. One is located north of Omiya Station, where trains for the Joetsu and Hokuriku Shinkansen lines diverge from the Tohoku Shinkansen. The second is at a switch north of Takasaki Station where the Joetsu and Hokuriku lines split. A third flyover is currently being constructed at Fukushima Station. This new elevated track is expected to open for service in 2026, allowing Yamagata Shinkansen services to continue northward on the Ou Main Line.

The Netherlands is another country with extensive use of these junctions. There are between 25 and approximately 40 flying junctions across the Dutch railway system. Some of these are used where two lines merge to become a four-track railway. In these cases, the tracks are paired by direction to increase capacity. Examples of these complex junctions include the areas around Amsterdam Sloterdijk, Duivendict, and the exits of Utrecht Centraal and Rotterdam Centraal. Some junctions, like the one near Harmelen, are noted for their history regarding previous rail accidents before they were converted to flying junctions.

In the United States, flying junctions are vital for managing busy urban transit systems. In the Northeast Corridor, tracks converge at Zoo Junction near 30th Street Station in Philadelphia. In Boston, the MBTA Green Line uses an underground flying junction west of Kenmore station. The Red Line in Boston also utilizes a flying junction north of the JFK/UMass station to manage different branches. Chicago’s "L" system also employs these structures. For example, an underground flying junction separates Red Line trains at certain points to manage service to the South Side and 95th.

Flying junctions connect different railway systems and allow for much higher efficiency. By separating the paths of trains, these structures prevent the need for complex interlocking signals required at flat junctions. They allow for the seamless integration of high-speed lines, commuter rails, and heavy freight. Whether through a massive bridge or a deep tunnel, these junctions keep the global movement of people and goods organized.

Without them, the speed and reliability of modern rail travel would be impossible to maintain.