Lack of space in the track section? When track changes in curves become necessary, a special solution is used: the inner curve turnout (IBW).
If a track change within a curve is necessary in narrow track fields, a standard turnout is not sufficient. This is where a special type of turnout technology comes into play: the inner curve turnout (IBW). It makes it possible to route the branch and main track completely in a curve – and thus makes efficient use of the available track space.
Bharat Forge CDP Railsystems supplies operationally reliable components for such applications – manufactured with technical precision and tailored to the requirements of modern railroad infrastructure. Whether in stations, shunting areas or at transfer points: The inside curve turnout is indispensable where radii are limited but high availability is required.
Definition and function of the inner curve switch
The inner curve turnout – IBW for short – is a special design within turnout technology. Its key feature: both track sections are completely curved. There is no straight section, no change of direction. This is precisely what makes them ideal for confined track areas, for example in railroad stations or industrial sidings.
It is created by selectively bending a simple turnout – but only in the area of the intermediate rails. The switch inclination and tangent lengths are retained. This requires precision in planning and execution.
Typical features of an IBW:
- The main track and branch are continuously curved
- The radius is limited – at least 175 m is required
- Curved rails in several areas, particularly on the tongue device, intermediate rails and in the frog area
- Centrifugal force and jerk tests are often necessary
- Used primarily where space is limited but lane changes are necessary
Classification into the switch types
The inner curve turnout belongs to the family of curved turnouts, but differs clearly from outer curve or transition curve turnouts. While at least one track section runs straight in other designs, the direction of both tracks remains curved in the IBW. For a better basic understanding, it is worth taking a look at the general structure of turnouts:
What is a Switch? Structure, Function and Significance in Rail Traffic
Structure and technical features
Inside curve turnouts (IBW) are created by selectively curving a simple turnout – but not only in the area of the intermediate rails. Switch rails and rails in the frog area are also adapted to the curve. The tangent length and the turnout inclination are generally retained.
The curvature is usually in the main track, but can also be distributed over both strands. This directly influences the permissible curvature jump – and therefore also the speed and the centrifugal force verification.
Typical technical features:
- Tangent lengths and inclination of the output switch remain unchanged
- Curvature is usually in the main track, but can be distributed
- For asymmetrical distribution: proof of jerk and centrifugal force required
- Combination of radii influences the speed and position of the turnout
Adapted components are used for the IBW, e.g:
You can find out more about the structure of a switch here.
Areas of application for the inner curve switch
Inside curve turnouts are used wherever tracks have to change within an existing curve – and the available space is limited. This applies in particular to sections of track where vehicles with defined track and wheel geometries have to be guided safely through curved switch areas.
Typical locations:
- Stations with parallel tracks
- Shunting and stabling facilities with dense switch points
- Industrial connections in a confined space
- Technically complex junctions, for example in combination with a double crossover point (DKW)
Advantages and challenges in operation
Inside curve turnouts are technically demanding – but in certain locations there is no alternative. Their special geometry offers operational advantages, but also poses planning and construction challenges.
Advantages:
- Space-saving routing – ideal for limited space in the track field
- Track change in a curve, without directional break or intermediate straight line
- Optimized usable length, e.g. in stations or parking areas
- Flexible installation in complex junctions
- Compatible with modular solutions, such as for turnout locks or frogs
Challenges:
- Increased planning effort, especially with asymmetrical curvature distribution
- Centrifugal force and jerk verification required – especially with elevated track position
- High demands on installation accuracy and maintenance
- Sensitive geometry in the area of the junction and the connection to the main track
The strengths of high-quality components – such as those from Bharat Forge CDP Railsystems – are particularly evident under cornering loads or with tight radii. They ensure safe, low-maintenance transitions – and thus contribute to the stability of the entire track.
Conclusion
The inside curve turnout is a technically sophisticated but extremely efficient solution for track changes in curves. Whether in real rail traffic or in model construction – it enables complex track layouts in confined spaces and contributes to smooth operation. Careful planning, suitable radii and a high-quality design of the mechanical components are crucial for successful use.
Frequently asked questions about the inner curve switch (IBW)
Which design is the basis for an inside curve turnout?
Inside curve turnouts are generally based on standardized simple turnouts. The respective design depends on the desired radius, the route and the function (e.g. branching speed). The basis is always a testable geometry with a clearly defined curvature.
How are IBWs driven on?
Driving on an inside curve turnout is only permitted if all technical verifications have been provided – in particular for the curvature jump, superelevation and lateral force effect. It is also important that all components are precisely mounted in the track.
Is there an article number or a code?
Types of turnouts – including inside curve turnouts – are usually given a technical code consisting of radius, inclination and design. In tenders or orders, the turnout is listed as an article with a specific designation.
How many units are needed per system?
This depends heavily on the concept of the respective railroad system – such as a station, industrial connection or transfer point. In modular systems, IMs are often tendered as a product in a package with other components (e.g. frog, closure, sleeper grid). The number of pieces depends on the track layout.
What needs to be considered for storage and track bedding?
Especially in curved positions – as with inner curve turnouts – a stress-free bearing and exact fit in the track bed is crucial for operational safety. Particular attention must be paid to this:
- Stress-free position of the components to avoid deformation during operation
- Precise geometry when inserting into the track – especially in the area of the switch device and the frog
- Factory pre-assembly of individual components facilitates subsequent installation and ensures reproducible quality
- Proper storage prevents corrosion and warping – ideally on stable storage racks with weather protection
Bharat Forge CDP Railsystems supplies the appropriate system components – such as sliding chair plates or tongue rolling devices – ready for installation and in tested quality.
Is there an EIA for inside curve turnouts?
In real railroad construction, prices are not communicated via an RRP (recommended retail price), but via project-specific offers. The material value depends heavily on the type of construction, the desired quantity and the general conditions (e.g. installation location, radius, technical equipment).
What is a curved turnout?
A curved turnout is a type of turnout where at least one track – the main track and the branch – runs in a curve. It is used when a track change has to take place within a curve.
A distinction is made:
- Inner curve turnout (IBW): Both tracks are curved, curve centers are on the same side.
- Outside curve turnout (ABW): The main and branch tracks bend in opposite directions.
Curved turnouts enable space-saving alignments – but place higher demands on planning and execution.