Flyover: Types, Design, and Advantages

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A flyover is a high-level road bridge that crosses over another railroad or highway intersection or an existing road. It is also called an “overpass.” 

In order to prevent traffic congestion below, flyovers are constructed to allow for safe passage over obstacles. A road, highway, or railroad may be required for the passage.

A bridge and a flyover differ from one another depending on how they will be used and where they will be constructed.

Bridges are constructed to link two separate locations; these locations may be found naturally in places like valleys, rivers, seas, or other water bodies. Whereas a flyover is constructed to connect two points in congested areas, such as roads and highway intersections.

Types of Flyovers

The two types of flyovers used for traffic management are:

1. Simple Flyovers

This particular flyover is the one that is used the most often. This type of highway is used for fast-moving traffic to cross railway lines or heavy vehicular junctions.

2. Cloverleaf Flyovers

Cloverleaf flyover is a form of grade separator as well. In this kind of flyover, the grade separation technique allows traffic from one or more roads to pass the junction without directly crossing it or interfering with the flow of other traffic streams. 

Since there is no need to weave or slow down, this offers an advantage over the simple flyover.

Classification of Flyover based on Form

1. Overpass Flyover

An overpass flyover is one that is built over an existing highway or railway line that crosses over barriers. The primary purpose of an overpass flyover is to keep other traffic away from the railway path (i.e., vehicle and pedestrian traffic).

2. Underpass Flyover

An underpass flyover crosses over an existing railroad crossing, road, or other obstacles underneath. An underpass flyover is often built to allow cars and people to pass without disrupting the railroad and road. Both flyovers improve traffic control, which immediately lowers the accident rate.

Classification of Flyovers based on Material

1. Composite Flyover 

A composite flyover is a combination of both RCC and steel elements acting together. The strength of both RCC and steel together contributes to the strength of a composite flyover. Steel girders may be rolled steel joists (like ISMB, ISWB, ISHB) for short spans up to about 10 m or plate girders (built-up beams) for longer spans.

2. Steel Flyover

Steel flyovers are those which use steel as their primary structural material. This kind of flyover is more cost-effective than the composite and concrete flyovers. Because it is comprised of steel, fluctuations in temperature might cause issues with expansion and contraction; as a result, the steel should be coated or galvanized to prevent these issues.

3. Concrete Flyover 

Concrete is the main component used to construct concrete flyovers with steel. Concrete flyovers are further divided into precast and cast in-situ concrete flyovers.

Advantages of Flyover Bridge

The following are the advantages of using a flyover:

1. It is useful for traffic management.
2. Reduces travel time due to less congestion
3. Improves pedestrian safety
4. Provides space for emergency vehicles to move quickly.

Disadvantages of Flyover Bridge

The following are the disadvantages of using a flyover:

1. They typically require a large space; thus built-up environments are not good for them.
2. Though the accident risk is reduced, the damage will be significant, if one does happen. There is a lower chance of survival in accidents since the vehicle is at a height.
3. It is extremely expensive to construct.

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