2.2.3. Reverse curves

A reverse curve is made up of two equal or different radii bending in opposite directions with a common tangent at their junction. Their centres would lie on opposite sides of the curve.

Reverse curves consist of two arcs that turn in opposite directions. Imagine you are driving and have to turn left and then immediately turn right to continue on the road; that’s similar to what a reverse curve does. The common tangent is the straight line you would follow before and after making these turns, helping to smoothly connect the two different turns.

Think of reverse curves like a figure-eight track used for toy cars, where one loop turns in one direction and then immediately leads into a second loop that turns in the opposite direction. This design allows the cars to flow smoothly from one direction to another.

Reverse curves are used when the straights are parallel or intersect at a very small angle. They are commonly used in railway sidings, and sometimes on railway tracks, and is meant for low speeds.

Reverse curves are particularly useful in scenarios where straight paths would intersect at a sharp angle, making it difficult or unsafe for vehicles to navigate. These curves allow the transition from one direction to another without requiring drastic turns, thus facilitating smoother movement. They are often utilized in railway sidings where trains need to change direction gradually.

Imagine a small train station with tracks that need to accommodate trains coming from two directions. The use of reverse curves helps the train switch tracks smoothly without making sharp turns, akin to a skateboarder moving smoothly around a bowl instead of attempting abrupt stops or turns.

Reverse curves should be avoided as far as possible on main railway lines and highways where speeds are high.

While reverse curves are beneficial in certain situations, they should not be used in high-speed areas due to safety concerns. At higher speeds, the sudden change in direction can be dangerous for vehicles, increasing the risk of accidents. Hence, planners aim to limit the use of reverse curves in busy transport routes to maintain safety and efficiency.

Consider a racetrack where cars are racing at high speeds; if the track suddenly bends in the opposite direction, it could lead to crashes or loss of control. Just like in racing design, transport planners must consider how sharp turns impact safety and speed when designing roads.

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