Guidelines on Design and Installation of Road Traffic Signals

IRC 93 Scope Summary: Specifications for Road Traffic Signals

• Scope: IRC 93 covers design, installation, and maintenance of road traffic signals including:
  • Signal visibility and location
  • Signal foundation design
  • Signal phasing and timing based on traffic volume
  • Electrical and cable layout specifications

Key Tables & Figures

Important Specifications

• Minimum Visibility Distance depends on approach speed (see Table 1).
• Signal Foundation: Refer Fig. 4 for typical foundation details ensuring stability under wind and pole loads.
• Signal Timing: Cycle timings are based on vehicular volume (Tables 2 & 3).
• Phasing: Use signal phasing diagrams (Fig. 6) for coordinated traffic flow.

Example: Minimum Visibility Distance (m)

flowchart TD
    A[Traffic Volume] --> B{Warrant Check}
    B -->|Meets Warrant-1| C[Install Signal]
    B -->|Meets Warrant-2| C
    B -->|No Warrant| D[No Signal Required]
    C --> E[Design Signal Foundation]
    E --> F[Install Signal Pole & Cable Layout]
    F --> G[Set Signal Timing & Phasing]

For detailed design, consult IRC 93 full document, especially Tables 1-3 and Figures

Warrants for Installation of Traffic Signals (IRC 93)

1. Warrant 1 - Minimum Vehicular Volume (Clause 2.5, Table 2)

Signal installation is warranted if, for any 8 hours/day, traffic volumes meet:

• If 85th percentile speed > 50 kmph or population < 2.5 lakhs, minimum volumes reduce to 70%.

2. Warrant 2 - Interruption of Continuous Traffic (Table 3)

Signal warranted if, for any 8 hours/day:

3. Signal Timing (Clause 2.8)

• Lane width = 2.8 m.
• Max 4 phases per cycle.
• Green time apportioned proportional to vehicles per lane.
• Reaction time for first vehicle = 6 sec, headway for others = 2 sec.

4. Required Data for Signal Justification

• Hourly vehicle counts (10 consecutive hours).
• Peak period vehicle classification.
• Pedestrian volumes.
• 85th percentile speeds.
• Intersection geometry & collision history.

flowchart TD
    A[Traffic Study] --> B{Meets Warrants?}
    B -- Yes -->

IRC 93: Signal Heads and Indications – Key Specifications

1. Signal Types & Colors (Clause II)

• Green Signal: Proceed indication.
• Steady Amber Signal: Caution, prepare to stop.
• Steady Red Signal: Stop.
• Flashing Signal: Special caution or stop depending on context.
• Pedestrian Signal: Walk/Don't Walk indications.

2. Size and Design of Signal Lenses

• Standard lens diameter: 300 mm (typical for vehicular signals).
• Lens arrangement: Vertically aligned (Red on top, Amber middle, Green bottom).
• Illumination: Uniform brightness for visibility at required distances.

3. Visibility & Location

• Signal face height: Typically 5.5 m to 6 m above road level.
• Transverse location: Positioned for clear visibility without obstruction.
• Use of visors (300 mm) to reduce glare and improve clarity.

4. Signal Phasing & Timing (Refer Figures 6, 8, 9)

• Green period, amber period, and red period must be coordinated.
• Flashing operation for off-peak or special conditions.
• Time-distance diagrams ensure smooth traffic flow.

5. Foundations & Supports

• Typical foundation depth and design per Fig. 4.
• Poles must withstand wind loads and vibrations.

Summary Table: Signal Lens Sizes & Heights

flowchart TD
    A[Red Lens (Top)] --> B[Amber Lens (Middle)]
    B --> C[Green Lens (Bottom)]
    C --> D[Signal Face with Visor]
    D --> E[Mounted at 5.5-6 m Height]
    E --> F[Visible to Road Users]

For detailed timing and coordination, refer to Appendices 2 & 3 in IRC 93 for signal cycle design based on traffic volume.

Note: For exact timings, phasing, and controller specs, consult IRC 93 sections on signal phasing and controller functional specifications.

IRC 93 - Signal Operation Relating to Traffic Flow

Though the code lacks direct formulas in the provided context, key references and specifications include:

Key Tables & Clauses:

• Cycle Timings Based on Vehicular Volume (Appendix 2 & 3, Pages 35 & 37)
• Minimum Vehicular Volume Warrants (Warrant 1 & 2, Pages 25-26)
• Green Period in Signal Phasing (Page 21)
• Signal Phasing and Band Diagrams (Fig. 6, Page 31)

Important Concepts & Formulas:

1. Cycle Length (C) Calculation (approximate): [ C = \frac{1.5L + 5}{1 - Y} ]

   • L: Total lost time per cycle (s)
   • Y: Sum of critical flow ratios (flow/saturation flow)

2. Green Time (g) for a phase: [ g = \frac{y}{Y} (C - L) ]

   • y: Critical flow ratio for the phase

3. Lost Time (L): Includes start-up delays and clearance intervals.

4. Minimum Green Time: To ensure pedestrian crossing and vehicle start-up.

Signal Operation Guidelines:

• Adjust cycle length based on vehicular volumes and warrants.
• Ensure minimum visibility distances (Table 1) for approach speeds.
• Use flashing operation during low traffic or off-peak hours.
• Maintain continuity of operation and regular maintenance.

Diagram: Signal Timing Cycle Components

gantt
    title Signal Cycle Timing
    dateFormat  s
    section Cycle Components
    Lost Time (L)          :done, 0, 5
    Effective Green (g)    :done, 5, 25
    Clearance Interval     :done, 30, 5

Summary: Use IRC 93 Appendices 2 & 3 for detailed cycle design, apply warrants for signal installation, and ensure green times and cycle lengths suit traffic volumes for smooth flow.

IRC 93 Pedestrian Signal Guidelines: Key Points

1. Pedestrian Signal Types (Clause 5)

• Typically includes "Walk" (Green Man) and "Don't Walk" (Red Man) signals.
• Signals must be clearly visible and distinguishable from vehicular signals.

2. Signal Size & Design (Clause 6)

• Lens diameter: 300 mm standard for pedestrian signals.
• Use visors (Fig. 1) to reduce glare and improve visibility.

3. Signal Timing (From Time & Distance Diagrams, Figs. 8 & 9)

• Pedestrian crossing time should be calculated based on: [ t = \frac{L}{v_p} + t_{start} ] Where:
  • (L) = crossing length (m)
  • (v_p) = pedestrian walking speed (1.2 m/s typical)
  • (t_{start}) = start-up time (usually 3-5 seconds)

4. Location & Height (Clause 10 & 11)

• Signals must be placed at eye level for pedestrians, typically 2.1 to 2.4 m above ground.
• Position signals so they are directly in pedestrian line of sight.

5. Visibility & Shielding (Clause 9)

• Use signal visors and proper shielding to prevent sunlight interference.
• Ensure signals are visible from all pedestrian approaches.

Summary Table: Pedestrian Signal Specifications

flowchart LR
    A[Pedestrian Approaches] --> B[Pedestrian Signal]
    B --> C{Signal State}
    C -->|Walk (Green Man)| D[Crossing Allowed]
    C -->|Don't Walk (Red Man)| E[Wait]
    D --> F[Crossing Time Calculation]
    F --> G[Safe Crossing]

For detailed foundation, pole location, and wiring refer

IRC 93 - Size and Design of Signal Lenses

Key Specifications (Clause 6.1)

• Shape: All signal lenses must be circular.
• Sizes: Two standard net diameters after accounting for hoods:
  • 200 mm
  • 300 mm
• Usage:
  • 300 mm lenses are preferred for better visibility, especially in:
    • High-speed roads
    • Busy intersections
    • Locations requiring enhanced visibility

Additional Notes:

• The net diameter refers to the visible lens diameter facing the traffic, excluding the hood or visor.
• The design ensures uniformity and adequate visibility for drivers.

Summary Table:

flowchart TD
    A[Signal Lens] --> B{Size}
    B --> C[200 mm]
    B --> D[300 mm]
    D --> E[High-speed roads]
    D --> F[Busy intersections]

This ensures compliance with IRC 93 for signal lens design and visibility.

IRC 93 does not explicitly specify detailed formulas or tables for the Arrangement of Lenses in Signal Faces or the Size and Design of Signal Lenses. However, based on standard traffic signal engineering practices aligned with IRC guidelines:

Key Specifications for Signal Lenses:

• Lens Diameter: Typically 200 mm or 300 mm for urban signals; larger sizes for high-speed roads.
• Lens Color Arrangement:
  • Red at the top
  • Yellow in the middle
  • Green at the bottom
• Lens Type: Fresnel lenses are preferred for better light dispersion.
• Lens Spacing: Vertical spacing should allow clear visibility without overlap; usually, minimum 50 mm gap between lenses.
• Signal Face Size: Generally, a square face of 450 mm to 600 mm per side.

General Guidelines:

• Use uniform lens sizes in one signal face for consistency.
• Ensure proper alignment to avoid parallax errors.
• Signal faces must be clearly visible at the required distance (e.g., 100 m for urban roads).

flowchart TD
    A[Signal Face] --> B[Red Lens (Top)]
    A --> C[Yellow Lens (Middle)]
    A --> D[Green Lens (Bottom)]
    B --> E[Diameter: 200-300 mm]
    C --> E
    D --> E

For detailed design, consult IRC 93 Section 6 & 7 and relevant traffic signal standards.

The IRC 93 code does not explicitly provide clauses or formulas on Illumination of Lenses or Size and Design of Signal Lenses. However, based on standard traffic signal engineering principles and typical IRC practices, here are key points:

Illumination of Lenses (General Guidelines)

• Lens Illumination depends on the light source intensity and lens size.
• Use LED or incandescent lamps with adequate luminous intensity to ensure visibility.
• Ensure uniform illumination across the lens surface to avoid dark spots.

Size and Design of Signal Lenses

• Typical lens diameters:
  • Small signals: 200 mm (8 inches)
  • Medium signals: 300 mm (12 inches)
  • Large signals: 400 mm (16 inches) or more for high visibility.
• Lens color and material should comply with IRC 93 standards for durability and light transmission.
• Use Fresnel lenses or prismatic lenses for better light focusing.

Formula for Illumination (Approximate)

[ E = \frac{I}{d^2} ]

• (E) = illuminance on lens (lux)
• (I) = luminous intensity of the source (candela)
• (d) = distance from lamp to lens (meters)

Recommendations

• Ensure minimum illuminance per IRC or relevant traffic signal standards (~100-200 lux on lens surface).
• Use reflectors and diffusers behind lamps for uniform light distribution.

graph LR
A[Light Source] --> B[Reflector]
B --> C[Signal Lens]
C --> D[Observer's Eye]

For detailed design, refer to IRC 93 sections on traffic signals and consult IS 1944 for electrical illumination standards.

IRC 93 - Visibility and Shielding of Signal Faces

Though IRC 93 lacks explicit clauses on visibility and shielding, standard practice for 300 mm signal visors (as per typical IRC guidelines) includes:

Key Specifications:

• Signal Face Size: 300 mm diameter.
• Visor Dimensions: Typically, visors extend 50-75 mm beyond the signal face edge to reduce glare.
• Visibility Angle: Signal faces should be visible within a horizontal viewing angle of ±30° and vertical angle of ±15°.
• Shielding: Visors must shield the signal face from sunlight and vehicle headlight glare without obstructing visibility.

Typical Dimensions (Fig. 1 - 300 mm Signal Visors)

General Guidelines:

• Position signals at eye level for drivers (~1.2 to 1.5 m above road).
• Avoid obstructions like trees or poles.
• Use matte black visors to minimize reflection.

flowchart LR
A[Signal Face 300 mm] --> B[Visor extends 50-75 mm]
B --> C[Shields sunlight & glare]
C --> D[Maintains visibility ±30° horizontal]
C --> E[Maintains visibility ±15° vertical]

This ensures clear visibility and effective shielding of signal faces on roads.

IRC 93: Number and Location of Signal Faces

While IRC 93 does not explicitly prescribe formulas for the number and location of signal faces, key points based on standard traffic engineering practice and related IRC guidelines are:

Key Specifications:

• Number of Signal Faces:

  • At least one signal face per approach lane or group of lanes.
  • Additional faces for turning lanes or where visibility is restricted.

• Location of Signal Faces:

  • Positioned to ensure clear visibility to drivers from all approach lanes.
  • Typically mounted above the center of the lane or group of lanes.
  • Signals should be placed at a height of 5 to 7 meters above the road surface.
  • Horizontal offset should be such that signals are visible without obstruction (refer to Fig. 3 of IRC 93 for transverse location).

Visibility Guidelines:

• Signal faces must be visible from a minimum distance of 100 m for urban roads, more for high-speed roads.
• Use signal visors (e.g., 300 mm visors as per Fig. 1) to reduce sun glare and improve visibility.

Summary Table (Typical Signal Faces per Approach):

flowchart LR
    A[Approach Road] --> B{Number of Lanes}
    B -->|Single Lane| C[1 Signal Face]
    B -->|Multiple Lanes| D[Signal Faces per Lane or Group]
    B -->|Turning Lane| E[Additional Signal Face]
    C --> F[Position above lane center]
    D --> F
    E --> F

For detailed dimensions and foundation details, refer to Fig. 3 and Fig. 4 in IRC 93.

IRC 93 - Height of Signal Faces

According to IRC 93:

• Clause 11.1:
  For signal faces not suspended over the roadway, the bottom of the signal housing should be at a height of:
  2.5 m above the footpath
  or if no footpath exists,
  2.5 m above the pavement grade at the center (crown) of the roadway.

• Clause 11.2:
  For signal faces suspended over the roadway, the bottom of the signal housing should be at a height of:
  5.5 m above the pavement grade at the center of the roadway.

Summary Table

This ensures visibility and clearance for vehicles and pedestrians.

graph TD
  A[Signal Face] --> B[Not Suspended]
  A --> C[Suspended Over Roadway]
  B --> D[Height = 2.5 m above footpath or pavement]
  C --> E[Height = 5.5 m above pavement]

IRC 93: Transverse Location of Signal Supports & Controller Cabinets

While IRC 93 does not provide explicit clause numbers here, key points from the relevant sections and figures are:

Transverse Location of Signal Supports

• Signal poles should be located at a safe lateral distance from the edge of the carriageway to avoid vehicle collision.
• Typical transverse offset is 0.5 m to 1.0 m behind the curb or edge line, depending on road width and traffic speed.
• Refer Fig. 3 (Transverse Location of Signal Supports) for exact positioning relative to the carriageway and pedestrian paths.

Specifications for Signal Foundations

• Foundations must ensure stability against wind and vehicle impact.
• Typical foundation size: 1.0 m × 1.0 m × 1.0 m (depth × width × length) concrete block.
• Reinforcement details per Fig. 4 (Typical Foundation Details of Signal Pole).

Controller Cabinets

• Located at least 0.5 m away from the signal pole foundation.
• Positioned to avoid obstruction to pedestrian pathways and vehicle movement.
• Must allow easy access for maintenance.

Summary Table: Typical Transverse Offsets

Diagram Reference

graph LR
A[Carriageway Edge] --> B[Signal Pole (0.5-1.0 m offset)]
B --> C[Controller Cabinet (≥0.5 m from pole)]

Note: For detailed dimensions and reinforcement, consult IRC 93 Figures 3 & 4.

IRC 93 - Specifications for Signal Foundations

Though IRC 93 does not provide explicit formulas in the excerpt, typical signal foundation design follows these key principles:

Key Specifications:

• Foundation Type: Usually reinforced concrete, designed to resist bending moments from wind loads on the signal pole.
• Depth & Diameter: Foundation depth typically ranges from 1.0 m to 1.5 m, diameter from 0.5 m to 0.7 m, depending on soil conditions and pole height.
• Reinforcement: Use of vertical and horizontal steel bars to resist bending and shear.
• Embedment Length: Pole embedded at least 1/3rd of its height into the foundation for stability.

Typical Design Considerations:

• Wind Load (W):
  [ W = A \times P \times C_d ]

  • (A) = projected area of the signal face and pole (m²)
  • (P) = wind pressure (kN/m²) (as per IS 875 Part 3)
  • (C_d) = drag coefficient (usually 1.2 to 1.5)

• Moment at Base (M):
  [ M = W \times h ]

  • (h) = height of the pole above ground (m)

• Foundation Design:
  Use bending moment (M) and axial load (self-weight + pole weight) to design reinforcement and footing size.

Reference Table (Typical Dimensions):

Diagram: Typical Signal Pole Foundation

graph TD
A[Signal Pole] --> B[Embedded in Concrete Foundation]
B --> C[Reinforcement Bars]
B --> D[Foundation Diameter ~0.6m]
B --> E[Foundation Depth ~1.2m]

Note: For exact design, refer to IS 875 (Part 3) for wind loads and IS

IRC 93: Coordination of Traffic Control Signals

While IRC 93 provides detailed technical aspects for traffic signals, the coordination of traffic control signals is summarized under Clause 14 (page 19). Key points include:

Key Concepts for Coordination

• Signal Coordination aims to provide smooth traffic flow along corridors by linking signals.
• Use time and distance diagrams (see Fig. 8 & 9) for one-way and two-way streets.
• Coordination depends on:
  • Cycle length (C): Total time for one complete signal cycle.
  • Green time (g): Duration of green signal for a movement.
  • Offset (O): Time difference between start of green at successive signals.

Basic Formulas

• Cycle length (C) can be estimated by Webster’s formula: [ C = \frac{1.5L + 5}{1 - Y} ] where:

  • (L) = total lost time per cycle (seconds),
  • (Y = \sum \frac{d_i}{s_i}) (sum of flow ratios),
  • (d_i) = demand flow for phase i,
  • (s_i) = saturation flow for phase i.

• Offset (O) for two signals spaced (D) meters apart: [ O = \frac{D}{V} ] where (V) is the average vehicle speed (m/s) between signals.

Tables & Figures to Refer

Summary Diagram: Signal Coordination Concept

flowchart LR
    A[Signal 1 Green Start] -->|Offset O| B[Signal 2 Green Start]
    B --> C[Signal 3 Green Start]
    style A fill:#4CAF50,stroke:#333,stroke-width:2px,color:#fff
    style B

IRC 93: Flashing Operation of Traffic Control Signals

Key Points from IRC 93 (Clause on Flashing Operation, Page 19):

• Purpose: Flashing mode is used during off-peak hours, signal failure, or special conditions to control traffic safely.
• Types of Flashing:
  • Flashing Red: Acts as a stop signal; vehicles must stop and proceed when safe.
  • Flashing Amber (Yellow): Caution signal; vehicles may proceed with care.
• Operation Guidelines:
  • Flashing frequency typically between 60 to 120 flashes per minute.
  • Use flashing red at all approaches in case of total signal failure.
  • Use flashing amber on main road and flashing red on minor road during off-peak hours.
• Visibility: Signal faces must be clearly visible and shielded from confusing lights.
• Maintenance: Ensure continuous operation and proper synchronization during flashing mode.

Typical Flashing Signal Specifications:

Summary Diagram of Flashing Operation Logic:

flowchart TD
    A[Normal Signal Operation] --> B{Condition?}
    B -->|Off-peak hours| C[Flashing Amber on Main Road]
    B -->|Signal Failure| D[Flashing Red on all approaches]
    B -->|Special Conditions| E[Flashing Red on Minor Road, Amber on Main Road]
    C --> F[Proceed with Caution]
    D --> G[Stop and Proceed When Safe]
    E --> F

References: IRC 93, Section II, Clause 15 (Page 19) for detailed technical aspects.