5. Track geometrics, Construction and Maintenance, Transportation Engineering, CE 4006 (Same as CC 4006)

Rajasthan Polytechnic (BTER) February 27, 2025

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Written by Garima Kanwar | Blog: Rajasthan Polytechnic

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Subject: Transportation Engineering, CE 4006 (Same as CC 4006)

Branch: Civil Engineering 🏗️
Semester: 4th Semester 📚

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5.1 Alignment - Factors Governing Rail Alignment 🚂📏

Rail alignment refers to the precise positioning and direction of the railway track. The main factors that govern alignment include:

  1. Topography 🏞️: The natural terrain (hills, valleys, rivers) influences where and how the track is laid.

    • Example: In mountainous regions, cuttings (digging into the earth) or embankments (raised tracks) may be required.

  2. Geotechnical Conditions 🌍: Soil stability and rock conditions are important for ensuring the track's foundation is strong.

    • Example: Loose soil or rocky ground may require reinforced track beds.

  3. Curves and Straight Sections ⤴️: Track alignment includes both curves and straight sections. Curves are especially important as they need to be carefully designed for safety and efficiency.

  4. Environmental Impact 🌿: Track alignment should minimize the impact on the environment (like wildlife habitats and water bodies).

  5. Cost 💰: Budget constraints can influence the design choices, such as how much cutting or embankment is done.

  6. Operational Efficiency 🏃‍♂️: The smoother the transitions between straight and curved sections, the better the overall train operation.

5.2 Track Cross Sections 🛤️📐

Track cross sections represent the layout of the track from a vertical view, showing how it interacts with the surrounding environment.

5.2.1 Standard Cross Section of Single and Double Line in Cutting and Embankment

  1. Single Line in Cutting (Track is below ground level):
    🌳      🌳
    |        |     <- Vegetation on sides
   _________
  |         |  <-- Track bed and ballast
  |         |  <- Railway track
  |_________|  
     | | |     <- Side slope for stability
     | | |     
     \___/      <- Drainage to prevent water accumulation
  1. Double Line in Cutting (Two tracks in a cutting):
    🌳      🌳
    |        |     <- Vegetation on sides
   _________
  |    |    |  <-- Track bed and ballast
  |    |    |  <- Double tracks
  |____|____|  
     | | |     <- Side slope for stability
     | | |     
     \___/      <- Drainage system
  1. Single Line in Embankment (Track is raised above ground level):
    🌳      🌳
    |        |     <- Vegetation on sides
   _________
  |         |  <-- Track bed and ballast
  |         |  <- Railway track
  |_________|  
      | |      <- Side slope for stability
      | |     
     _|_|_     <- Drainage system
    /     \    
   /       \    <- Raised embankment
  1. Double Line in Embankment (Two tracks in embankment):
    🌳      🌳
    |        |     <- Vegetation on sides
   _________
  |    |    |  <-- Track bed and ballast
  |    |    |  <- Double tracks
  |____|____|  
      | |      <- Side slope for stability
      | |     
     _|_|_     <- Drainage system
    /     \    
   /       \    <- Raised embankment

5.2.2 Important Terms 📝

  1. Permanent Land 🌍: The land occupied by the track and supporting structures. This land cannot be easily changed or altered once used for railway construction.

  2. Formation Width 📏: The total width of the track bed, including the ballast, side slopes, and drainage systems. It's wider in embankments for better support and stability.

  3. Side Drains 🌧️: Drains placed beside the track to carry away water and prevent the track from becoming waterlogged. Proper drainage is essential to keep the track stable.

5.3 Railway Track Geometrics 🚂🛤️

Track geometry refers to how the track is designed in terms of curves, gradients, and other factors that affect train movement.

5.3.1 Gradient ⬆️⬇️

A gradient is the slope of the track. It can either be an upward gradient (track rises) or a downward gradient (track falls).

  • Upward Gradient ⬆️: This increases the effort needed to move a train uphill.

       _____
  /     \
 /       \  <- Steep slope (upward gradient)

  • Downward Gradient ⬇️: This allows trains to move faster, but braking becomes important to prevent runaway trains.


       _____
  \     /
   \___/  <- Steep slope (downward gradient)

5.3.2 Curves - Types and Factors Affecting ⤴️

Curves are sharp bends in the track. Different types of curves include:

  • Simple Curves: A curve with a constant radius.

  • Compound Curves: A series of curves with varying radii.

  • Reverse Curves: Two curves in opposite directions connected without a tangent.

Factors affecting curves:

  • Radius: The smaller the radius, the sharper the curve. Smaller curves cause discomfort and wear.
  • Superelevation (Cant): Banking the track to reduce centrifugal force.
  • Train Speed: Higher speeds require larger curves for safety.
  • Rolling Stock: Heavier trains require larger radii for safe operation.

5.3.3 Grade Compensation ⚖️

Grade compensation adjusts the gradient when there are changes in track elevation (e.g., in tunnels or over bridges) to ensure smooth train operation.

5.3.4 Super Elevation (Cant) 🌀

Super elevation (cant) is the banking of the track on curves. This helps balance the centrifugal force and provides a smoother ride.

            ____  <- Outside rail (higher)
           /    \
    ______/      \____
   |      🚂     | <- Train on the curve
   |_____________|   
        ____    <- Inside rail (lower)

5.3.5 Limits of Super Elevation on Curves ⛔

  • Too much super elevation can make the ride uncomfortable or cause instability.
  • Too little super elevation leads to high centrifugal forces and can cause accidents.

Maximum Cant: Typically 150 mm is the upper limit for normal tracks.

5.3.6 Cant Deficiency ⚠️

Cant deficiency occurs when the cant (super elevation) is insufficient on curves, leading to increased centrifugal force. In such cases, the train may need to slow down for safety.

5.3.7 Negative Cant ❌

Negative cant happens when the outside rail is lower than the inside rail. This can happen when the track transitions from a curve to a straight section, leading to instability.

5.3.8 Coning of Wheel 🛞

Coning of the wheel refers to the slight angle on the wheel's profile. This helps the wheel stay aligned with the track and reduces wear.

     _______
    /       \
   |    🚂   | <- Wheel with a cone shape
    \_______/

5.3.9 Tilting of Rail 🛤️

Tilting of the rail helps reduce the centrifugal forces acting on trains when they move through curves. It allows for smoother high-speed travel.

5.4 Branching of Tracks, Points, and Crossings 🔀

Branching of tracks refers to the points where tracks diverge to form different paths.

  1. Points: These are mechanical devices used to switch trains from one track to another.

  2. Crossings: Locations where two tracks intersect.

  3. Turnout Types:

    • Switch Points: These guide trains from one track to another at a junction.
    • Crossover: A setup allowing trains to switch between parallel tracks.
    • Scissor Crossover: A more advanced setup for better switching between tracks.

Track Junctions:

  • Crossover 🔄:
  |    ________     ________
  |   |        |   |        |
  |---|        |---|        |  <- Connecting track
      |________|   |________|
  • Scissor Crossover ✂️:
   |      ________       ________      |
   |     |        |     |        |     |
   |-----|        |-----|        |-----|  <- Multiple connections
         |________|     |________|

5.5 Station 🚉

Stations are points where trains stop to pick up passengers or cargo. A station includes:

  • Tracks for train movement
  • Platforms for passengers
  • Signaling systems for managing train operations

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Rajasthan Polytechnic (BTER)

Posted by Rajasthan Polytechnic (BTER)

Hi! I’m Garima Kanwar, founder of Rajasthan Polytechnic (BTER). This platform provides notes, PDFs, and video lectures for all Polytechnic branches (ME, CS, EE) and semesters to make learning easy .I ensure exam-focused, updated, and simple-to-understand content, along with academic updates and career guidance.

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