Guidelines for Expressways Part I

Scope of MORTH 278 Part 1 (Geometric Design & Related Elements):

• Definition & Terrain Classification: Defines expressway geometric design parameters based on terrain types (Table 1.01).
• Design Speeds: Speeds vary by terrain (Table 1.03).
• Cross-Sectional Elements: Includes right of way, lane width, edge strip, shoulder, median, and embankment design (Clauses 1.4, Tables 1.04 to 1.08).
• Sight Distance: Stopping and decision sight distances for safety (Tables 1.09 & 1.10).
• Horizontal & Vertical Alignment: Minimum radii, superelevation, transition curves, and vertical curve lengths (Tables 1.12 to 1.20).
• Safety Barriers: Design and placement for roadside and median barriers (Chapter 8, Tables 8.01 to 8.04).
• Acceleration/Deceleration Lengths: Adjustment factors for speed changes (Tables 2.06A, 2.06B).
• Other Key Features: Pavement design, drainage, tunnels, lighting, noise barriers, toll plaza, service areas, traffic signs.

Key Formula Example: Stopping Sight Distance (SSD)

[ SSD = V \times t + \frac{V^2}{2gf} ]

• (V) = speed (m/s)
• (t) = perception-reaction time (s)
• (g) = acceleration due to gravity (9.81 m/s²)
• (f) = coefficient of friction (Table 1.11)

Typical Cross-Section Elements Summary

For detailed values, refer to respective tables in Chapter

Terrain Classification as per MoRTH 278 Part 1

1. Terrain Classes by Cross Slope (Table 1.01)

• Short isolated varying terrain stretches are ignored.

2. Rise/Fall & Curvature Criteria (Table 1.02)

3. Building & Control Line Standards (Table 1.05)

Additional Notes:

• Level Terrain: Long sight distances, minimal construction difficulty.
• Rolling Terrain: Moderate slopes with some restrictions.
• Mountainous Terrain: Abrupt elevation changes requiring benching/excavation.
• Steep Terrain: >60% slope, generally not suitable for normal highway alignment.

flowchart TD
    A[Terrain Classification] --> B[Plain (<10% slope)]
    A --> C[Rolling (10-25% slope)]
    A --> D[Mountainous (25-60% slope)]
    A --> E[Steep (>60% slope)]

    B --> F[Rise/Fall 0-15 m/km]
    C --> G[Rise/Fall 16-30 m/km]
    D --> H[Rise/Fall >31 m/km]

    F --> I[Curvature

Key Formulas, Tables & Specifications for Embankment Design (MORTH 278 Part 1)

1. Embankment Height & Material Selection

• Height governs material type.
• Foundation soil nature critically influences design.

2. Minimum Embankment Elevation

• Top of sub-grade ≥ 1.0 m above High Flood Level (HFL) / water table.
• Exception: minimum 0.6 m difference allowed in difficult sites.

3. Slope Specifications

• Maximum slope: 1V : 2H (Vertical : Horizontal).
• Desirable slope for moderate height: 1V : 4H or flatter.
• High embankments may require steeper slopes with safety barriers.

4. Stability & Settlement Analysis

• Stability of formation width and subsoil at toe level must be ensured.
• Settlement analysis to avoid differential settlement and failure.

5. Structural Features

• Use only suitable materials (e.g., cohesive soil blanket over sandy core to prevent erosion).
• Embankment slope should be flat and rounded to fit topography and right-of-way.

Typical Embankment Slope Table

Stability Check (Simplified Factor of Safety, FS):

[ FS = \frac{\text{Shear Strength of Soil}}{\text{Shear Stress due to Embankment Load}} \geq 1.5 ]

flowchart TD
    A[Embankment Design] --> B[Select Material Based on Height]
    A --> C[Check Foundation Soil Properties]
    A --> D[Calculate Stability & Settlement]
    D --> E[Ensure FS ≥ 1.5]
    A --> F[Design Embankment Slope]
    F --> G[Max 1V:2H; Desirable 1V:4H]
    A --> H[Set Embankment Elevation]
    H --> I[≥ 1.0 m above HFL or ≥ 

Key Specifications & Selection Criteria for Safety Barriers (MORTH 278 Part 1, Clause 8.03):

Barrier Types & Parameters

Cable Barriers (For Interchange Ramps)

Super-elevation Design as per MoRTH 278 Part 1

Key Formula (Clause 1.7.3.1)

[ e + f = \frac{V^2}{127 R} ]

• e = Superelevation (m/m)
• f = Coefficient of friction (refer Table 1.11)
• V = Design speed (km/h)
• R = Radius of curve (m)

Limits on Superelevation

Notes on Attaining Superelevation (Clause 1.7.3.2)

• Superelevation is provided gradually using transition curves.
• This ensures smooth lateral acceleration changes and vehicle stability.

Summary Diagram: Forces on a Vehicle on a Curve

graph LR
    C[Centrifugal Force (C)]
    W[Weight of Vehicle (W)]
    R[Resultant Force (R)]
    e[Superelevation (e)]

    C --> R
    W --> R
    R --> e

Use this formula and limits to design safe and comfortable horizontal curves in highways.

Coordination of Horizontal and Vertical Alignment (MoRTH 278 Part 1 - Clause 1.10)

• Design Philosophy: Horizontal and vertical alignments must be designed together to ensure safety, utility, and aesthetics, producing a balanced 3D road geometry.

• Key Principles:

  • Avoid sharp horizontal curves near the apex of summit or sag vertical curves for safety.
  • Lengths of vertical and horizontal curves should be approximately equal.
  • Horizontal curves should generally be longer than vertical curves if exact matching is not possible.
  • Avoid flat horizontal curves combined with steep grades or excessive curvature with flat grades.
  • Vertices (points of curvature) of horizontal and vertical curves should coincide for a smooth, pleasing appearance.

• Visual Guidance: Refer to IRC:73 Fig.1.10A for good alignment coordination examples and Fig.1.10B for undesirable forms.

Important Specifications:

Summary Diagram of Alignment Coordination

graph LR
A[Horizontal Curve Vertex] --- B[Vertical Curve Vertex]
B --> C[Balanced Lengths]
C --> D[Improved Safety & Aesthetics]
A -. Avoid .-> E[Sharp curves near summit]
E -. Leads to .-> F[Poor visibility & unsafe conditions]

For detailed radii, superelevation, and transition curve lengths, refer to Clauses 1.7.2, 1.7.3, and 1.7.4 respectively in MoRTH 278 Part 1, Volume II.

Types of Interchanges (MoRTH 278 Part 1 - Clause 2.4)

Key Design Notes:

• **

MORTH 278 Part 1 — Expressway Capacity Calculation

Key Terminology (Clause 4.2.2)

• Capacity (C): Maximum hourly flow rate under prevailing conditions (vehicles/hour).
• Flow (q): Number of vehicles passing a point per hour.
• Density (k): Vehicles per km.
• Speed (v): km/h.

Capacity Calculation (Clause 4.2.5)

The expressway capacity is computed using:

[ C = \frac{1000}{h} ]

Where:

• ( h ) = average headway (seconds) between vehicles at capacity.

Alternatively, capacity can be estimated by:

[ C = S \times D ]

Where:

• ( S ) = Saturation flow rate (vehicles/hour/lane)
• ( D ) = Number of lanes

Typical Values (from MORTH guidelines & empirical data):

Notes:

• Adjust capacity for lane width, gradient, and vehicle mix.
• Capacity reduces with heavy vehicle percentage increase.

Summary Diagram:

flowchart LR
    A[Traffic Flow q] --> B[Density k]
    B --> C[Speed v]
    C --> D[Capacity C = q_max]
    D --> E[Depends on headway h and lanes D]

Use MORTH 278 Part 1 for detailed adjustment factors and empirical tables.

Key Formulas and Specifications for Tunnel Ventilation (MORTH 278 Part 1)

1. Ventilation Types & Airflow Direction

2. Jet Fan Ventilation Limits

• Max longitudinal air velocity: Typically limited to 6–8 m/s for comfort and safety.
• Jet fans inject air to maintain airflow; spacing and number depend on tunnel length and traffic.

3. Saccardo Nozzle System

• Air injected at 15°–20° to tunnel axis.
• Air velocity through nozzle gap: 25–30 m/s.
• Fans mounted at portal feed air through nozzles to create longitudinal flow.

4. Energy Consumption Relation

[ \text{Energy} \propto \frac{L^4}{A^2} ]

• (L) = Tunnel length
• (A) = Duct cross-sectional area

Energy consumption increases sharply with tunnel length; larger ducts reduce energy needs.

5. Selection Criteria

• Fresh air demand (CO, NOx, opacity)
• Reliability & safety (fire control)
• Energy & investment cost
• Service friendliness

Summary Diagram: Ventilation Types

flowchart LR
    A[Tunnel Ventilation Systems] --> B(Longitudinal)
    A --> C(Semi-Transverse)
    A --> D(Fully Transverse)
    A --> E(Natural)

    B --> B1[Jet Fans / Saccardo Nozzles]
    C --> C1

Median Drainage - Key Points from MORTH 278 Part 1 (Clause 7.2.4)

• Median slope: Preferably 1:6, but 1:4 slope is acceptable.

• Design factors for inlet spacing:

  • Design discharge (Q)
  • Longitudinal slope (S)
  • Capacity of median channel
  • Flow velocity (v)

• Typical details: Refer to Figs. 7.04A and 7.04B for median drainage outfall and catch pit arrangements.

Hydraulics & Design Formulas (Clause 7.3.1)

• Manning’s formula for flow velocity (v):

[ v = \frac{1}{n} R^{2/3} S^{1/2} ]

Where:

• ( n ) = Manning’s roughness coefficient

• ( R = \frac{A}{P} ) = Hydraulic radius (m)

• ( S ) = Channel slope (m/m)

• ( A ) = Cross-sectional flow area (m²)

• ( P ) = Wetted perimeter (m)

• Discharge (Q):

[ Q = A \times v = \frac{1}{n} A R^{2/3} S^{1/2} ]

• Modified formula for shallow triangular channels:

[ Q = 0.375 \times S^{0.5} \times d^{2.667} / n ]

Where:

• ( d ) = Maximum flow depth (m)

Specifications Summary

• Median drains should be designed for adequate cross-section, slope, and capacity.
• Drains may be open or covered; covers must withstand wheel loads.
• Outfalls should minimize erosion.
• Use IRC:SP:42 and IRC:SP:50 for detailed drainage design.

flowchart TD
    A[Rainfall] --> B[Surface Runoff]
    B --> C[Median Drainage Channel]
    C --> D[Inlet Spacing (Q, S, Capacity, Velocity)]
    D --> E[Discharge through Cross Drainage]
    E --> F[Outfall with Erosion Control]

Note: Refer to MORTH Figs. 7.04A & 7.04

Crash Cushions as per MoRTH 278 Part 1

Crash cushions are designed to absorb vehicle impact energy safely, reducing occupant injury by controlled deceleration.

Key Concepts (Clause 8.7.1)

• Kinetic Energy Principle: Energy absorption by deformation or displacement.
• Conservation of Momentum Principle: Controlled momentum transfer to reduce impact forces.

Applications (Clause 8.7 & 8.13)

• Shield bridge rail ends, piers, median barriers.
• Protect construction/maintenance zones with portable cushions.
• Installed at toll plazas and gore areas (exit ramp junctions).

Important Specifications:

• Must absorb energy corresponding to design vehicle speed and mass.
• Should be compatible with longitudinal barriers.
• Portable cushions for temporary work zones.

Typical Design Parameters:

Energy Absorption Formula (Kinetic Energy Principle)

[ E = \frac{1}{2} m v^2 ] Where:

• (E) = energy to be absorbed (Joules)
• (m) = vehicle mass (kg)
• (v) = impact velocity (m/s)

flowchart LR
    A[Vehicle Impact] --> B[Crash Cushion]
    B --> C[Energy Absorption]
    C --> D[Controlled Deceleration]
    D --> E[Reduced Injury Risk]

Summary: Crash cushions must be selected/designed based on expected vehicle mass and speed, installed at vulnerable points like gore areas, bridge piers, and toll plazas, ensuring compliance with MoRTH guidelines for highway safety.

Advance Guide Signs (MORTH 278 Part 1, Clause 9.2.2.1)

• Purpose: Notify drivers well in advance of the exit point for principal destinations at the next interchange.
• Placement distances:
  • 2 km before exit
  • 1 km before exit
  • 500 m before exit
• Distance notation: Use whole kilometers only; no fractions or decimals.
• Right exit: Use diagrammatic signs for clarity.
• Typical layout: Refer Fig. 9.03 for standard interchange advance guide sign design (shows destination names and distance).

Summary Table for Advance Guide Sign Placement

This ensures consistent driver information and safety approaching interchanges.

Slippery When Wet Sign - Key Specifications (MORTH 278 Part 1)

Placement & Purpose (Clauses 9.8.6 & 9.26)

• Purpose: Warn drivers of potential slippery conditions when wet.
• Placement:
  • In advance of slippery sections.
  • Additional signs at intervals on long slippery stretches.
• Safe Wet Speed: Should be at least 10% lower than posted max speed.

Skid Resistance Guidelines (Clause 4.05)

Pavement Surface Requirements (Clause 4.01)

Summary Diagram: Sign Placement & Skid Resistance

flowchart LR
    A[Start of Slippery Section] --> B[Place Slippery When Wet Sign]
    B --> C{Long Slippery Section?}
    C -- Yes --> D[Place Additional Signs at Intervals]
    C -- No --> E[No Additional Signs]
    style B fill:#f9f,stroke:#333,stroke-width:2px
    style D fill:#bbf,stroke:#333,stroke-width:2px

Note: Use skid resistance testing equipment (SCRIM, Pendulum, ASTM Skid Trailer) to verify pavement safety and sign necessity.

Open Toll System (MORTH 278 Part 1 - Clauses 10.01, 10.2.3, 10.07)

Definition:

• Users pay a fixed toll at main lane plazas only.
• No toll plazas at every entry/exit ramp.
• Does not track travel distance or capture all users.
• Benefits: retrofitting existing roads, tolling long-distance users, allowing local traffic free access, and reducing operational costs.

Key Features:

• Main Lane Toll Plazas collect tolls.
• Ramp plazas are absent or limited.
• Lower installation and labor costs.
• Suitable for corridors with mixed local and through traffic.

ETC System Components (Fig. 10.07):

• ETC Onboard Units (OBUs)
• DSRC Roadside Radio Equipment
• Management and Back Office Systems (ID, fee payment, mileage management)
• Fee Display Units & CCTV

Toll Plaza Design Considerations:

• Mainline plazas sized for peak traffic flow.
• Booth numbers based on traffic volume and vehicle mix.
• Integration of ETC for faster processing.

Typical Formula for Toll Plaza Lane Calculation:

[ N = \frac{Q_p}{S \times H} ]

Where:

• (N) = Number of toll lanes
• (Q_p) = Peak hour traffic volume (vehicles/hour)
• (S) = Service rate per lane (vehicles/hour/lane)
• (H) = Hourly operating efficiency factor (typically 0.8 to 0.9)

flowchart LR
    A[Vehicle Approaches Toll] --> B{Open Toll System}
    B --> C[Main Lane Toll Plaza]
    C --> D[Fixed Toll Collected]
    D --> E[Vehicle Proceeds]
    B --> F[No Ramp Toll Plazas]
    F --> E
    E --> G[ETC System (Optional)]
    G --> H[DSRC Communication]
    H --> I[Back Office Processing]

Summary: Open toll systems simplify toll collection by fixed charges at main plazas, suitable for corridors prioritizing cost efficiency and long-distance tolling, often integrated with ETC for improved operation.

Key Specifications & Components of ETC System (MORTH 278 Part 1)

1. IC Card (On-Board Unit - OBU)

• Contact-less IC card per ISO/IEC 14443 Type A/B (basic).
• Optional: Contact or combined IC card per ISO/IEC 7816.
• Supports prepaid payment; recharge via toll plazas, Internet, or credit cards (e.g., VISA).

2. On-Board Unit (OBU)

• Types: One-piece or Two-piece.
• Power: Battery or vehicle power plug.
• Must withstand in-vehicle environmental conditions.
• Example: OBU with IC card (Fig. 10.10A).

3. Roadside Equipment

• Uses antenna system for communication.
• Vehicle classification done via OBU info; roadside does not classify vehicles.
• Enforcement cameras installed on gantries or roadside (Fig. 10.10B).

4. Toll Evasion Countermeasures

• License plate images captured by enforcement cameras.
• License plate data from road-vehicle communication matched with images to detect evasion.

5. System Configuration (Fig. 10.07)

• Components:
  • ETC Onboard Units
  • DSRC Roadside Radio Equipment
  • Management & Back Office Systems (ID management, fee payment, credit systems)
  • Enforcement CCTV & Fee Display Units

Summary Table

flowchart LR
    A[Vehicle with OBU & IC Card] -->|DSRC Communication| B[Roadside Radio Equipment]
    B --> C[Fee Payment Server]
    C --> D[Back Office Systems]
    B --> E[Enforcement