Guidelines for Variable Message Signs

IRC SP 85 - Scope (Clause 2) Summary:

The Scope of IRC SP 85 covers the specifications and standards for Variable Message Signs (VMS) used on highways, including:

• Types of VMS: Changeable Message Signs (CMS), Dynamic Message Signs (DMS), and Portable VMS.
• Purpose: To provide real-time traffic information, warnings, and public service announcements.
• Applications: Urban and rural highways, temporary and permanent installations.
• Technical Coverage: Mechanical design, sign equipment, communication, power, and control systems.
• Operational Aspects: Principles, message content, display requirements, and usage guidelines.

Key Points:

Reference Table: Abbreviations

For detailed formulas, design criteria, and technical specs, refer to respective clauses (10-22) in Part-B Technical.

flowchart TD
    A[Scope of IRC SP 85] --> B[Types of VMS]
    A --> C[Operational Guidelines]
    A --> D[Technical Specifications]
    B --> B1[CMS]
    B --> B2[DMS]
    B --> B3[Portable VMS]
    C --> C1[Message Content]
    C --> C2[Display]
    D --> D1[Mechanical Design]
    D --> D2[Communication]
    D --> D3[Power & Control]

**Use this scope as the foundation to navigate detailed clauses for design and

Purpose and Application of VMS (IRC SP 85)

Key Points from the Code:

• Purpose (Clause 4):
  VMS (Variable Message Signs) provide real-time traffic information to drivers, enhancing safety and traffic management.

• When to Use VMS:

  • Urban streets with clear sight distance ≥ 150 m (plain/rolling terrain).
  • In hilly terrain, sight distance depends on design speed.
  • No advertising allowed on the front panel.

• Design Process (Clause 22.2):

  1. Preliminary Data Collection:
     • Purpose of VMS
     • Information type to display
     • Alternative route/diversion points
  2. Determine VMS Type:
     • Based on purpose, info type, and technology (e.g., LED, flip-dot)
  3. Corridor Placement:
     • Select locations ensuring visibility and relevance.

• Controller (Clause 11.4):
  VMS controllers manage message display and communication with traffic management centers.

Summary Table: VMS Deployment Criteria

flowchart TD
    A[Start: Need for VMS] --> B[Collect Data: Purpose, Info, Routes]
    B --> C[Select VMS Type: Purpose & Technology]
    C --> D[Determine Placement: Sight Distance & Corridor]
    D --> E[Install Controller & Integrate]
    E --> F[Deploy & Monitor VMS]

Use this framework to ensure effective VMS deployment per IRC SP 85.

IRC SP 85: Variable Message Signs (VMS) - Key Points

Though IRC SP 85 lacks explicit clauses, general engineering practice and IRC guidelines provide the following essentials for VMS types:

Types of Variable Message Signs

• Fixed VMS: Permanently installed, used on highways/urban roads.
• Portable VMS: Mobile units for temporary traffic management.
• Trailer-mounted VMS: Portable, trailer-based for easy relocation.
• Overhead VMS: Mounted on gantries for maximum visibility.
• Side-mounted VMS: Installed on roadside poles or walls.

Key Specifications

• Character Height: Minimum 300 mm for urban arterial roads.
• Viewing Distance: Character height (mm) × 150 = viewing distance (m).
• Brightness: Adjustable to ambient light; typically 600-800 cd/m² daytime.
• Font Style: Clear, sans-serif fonts for legibility.
• Display Type: LED matrix preferred for clarity and energy efficiency.

Sample Viewing Distance Formula

[ \text{Viewing Distance (m)} = \text{Character Height (mm)} \times 150 ]

Typical Character Height vs Viewing Distance

flowchart LR
    A[Types of VMS] --> B[Fixed]
    A --> C[Portable]
    A --> D[Trailer-mounted]
    A --> E[Overhead]
    A --> F[Side-mounted]

Summary: Choose VMS type based on location and mobility needs, ensure character height fits viewing distance, and use LED displays for clarity and adaptability.

IRC SP 85 – Message Content & Formatting for Variable Message Signs (VMS)

Key Points from IRC SP 85:

• Message Types:

  • Incidents and traveler info
  • Public Service Announcements (PSA)
  • Special event, construction, evacuation, truck restrictions

• PSA Rules:

  • Use sparingly to maintain VMS effectiveness.
  • No PSA during urban peak hours.
  • No advertising allowed.
  • PSA must have prior authority approval.
  • Driver safety messages allowed only if supported by other media.
  • Display max 2 hours/day per board, staggered timings.

• Message Content:

  • Must be concise, clear, and brief for quick driver comprehension.
  • Display in English, Hindi, and local language.
  • Use alphanumeric characters and relevant pictorial signs.
  • VMS should default to blank mode when no messages are needed.

Recommended Message Formatting Guidelines:

Message Writing Tips:

• Use simple words and phrases.
• Avoid abbreviations unless universally understood.
• Prioritize critical info first (e.g., location, type of incident).
• Use standard pictograms for quick recognition.
• Avoid multiple messages at once; keep to one clear message per display.

flowchart LR
    A[Start: Need to Display Message?] --> B{Message Type?}
    B -->|Incident| C[Display Incident Message]
    B -->|Traveler Info| D[Display Traveler Info]
    B -->|PSA| E[Check Approval & Timing]
    E --> F{Approved & Off-Peak?}
    F -->|Yes| G[Display PSA (max 2 hrs/day, staggered)]
    F -->|No| H[Do Not Display PSA]
    C & D & G

Situations for VMS (Variable Message Sign) Use - IRC SP 85

Key Specifications & Guidelines:

• Purpose of VMS:
  To provide real-time traffic information, warnings, or route guidance to drivers.

• When to Use VMS:

  • On urban street segments with clear sight distance ≥ 150 m in plain/rolling terrain.
  • In hilly terrain, sight distance depends on design speed for legibility.
  • Avoid using front panels for advertising.

Design Process (Clause 22.2):

1. Preliminary Data Collection:

   • Intended purpose (e.g., traffic alerts, diversions)
   • Type of information to display
   • Alternative route diversion points

2. Determine VMS Type:

   • Based on purpose and information type
   • Choose VMS technology (LED, LCD, etc.)

3. Corridor Placement:

   • Select locations ensuring visibility and relevance to traffic flow

Summary Table for Sight Distance:

flowchart TD
    A[Start VMS Design] --> B[Collect Preliminary Data]
    B --> C[Determine VMS Type]
    C --> D[Select Corridor Placement]
    D --> E[Install & Monitor VMS]

Note: Always use engineering judgment for specific site conditions beyond these guidelines.

Key Specifications & Formulas from IRC SP 85 on Message Comprehension and Familiarity

1. Message Familiarity (Clause 6.6)

• Use common language to reduce comprehension time.
• Prefer day abbreviations ("TUES-FRI") over calendar dates ("OCT 1 - OCT 4").
• Avoid ambiguous terms like "FOR 1 WEEK"; use specific days ("WED-TUES").
• Display highway/route numbers with destinations for clarity.
• Messages can span multiple lines on VMS for better readability.

2. Message Length (Clause 6.5)

• Maximum 4 units of message load recommended.
• Average motorist can handle 8-word messages, with each word 4-8 characters (excluding prepositions).
• Number of panels/frames affects clarity.

3. Reading & Exposure Time (Clause 6.1)

• Exposure time ≥ Reading time.
• Design for minimum legibility distance:
  • 300 m for expressways
  • 200 m for other roads
• Recommended message display time:
  • 15 sec for National Highways
  • 20 sec for access-controlled expressways

4. Maximum Number of Message Panels (Table 2)

• If only one message panel is used, blinking can be applied (e.g., ON 2s, OFF 1s).

Summary Diagram for Message Timing & Panels

flowchart TD
    A[Speed (km/h)] --> B[Exposure Time (s) for 300m]
    B --> C{Max Message Panels}
    C -->|70, 90 km/h

Key VMS Placement Requirements (IRC SP 85, Clauses 9.3 & 21.3):

• Distance from Decision Points:

  • Place VMS 2 km before interchanges/exits on National Highways/freeways.
  • Repeat signs every 500 m between 2 km and the exit.
  • Place an additional VMS 50 m before the decision point.

• Visibility & Location:

  • Provide minimum 200 m sight distance.
  • Ensure no obstruction by signs, poles, or objects.
  • Place on a level surface, off the shoulder, preferably behind crash barriers.
  • Avoid placement within intersections or interchanges.
  • Do not interfere with other traffic control devices.
  • Position so it does not affect traffic flow; vehicle hosting VMS must be beyond safety distance from carriageway.

• Multiple VMS in Sequence:

  • Separate by at least 300 m.

• Operational Guidelines:

  • If no message for >4 hours, rotate sign panel parallel to road centerline, avoiding blank signs facing traffic.

• Character Size & Display:

  • Line matrix signs: 2 lines of text, character height 450 mm (Expressways) or 400 mm (National Highways).
  • Luminous intensity: 9000 cd/m².

Summary Table

flowchart LR
    A[2 km before interchange] --> B[Repeat every 500 m]
    B --> C[50 m before decision point]
    C --> D[Driver Reaction Time]
    D --> E[Safe Maneuver]

This placement ensures drivers have adequate time to perceive, comprehend, and react safely to the VMS messages.

Design of Variable Message Signs (VMS) – IRC SP 85 Key Points

1. When to Use VMS

• Urban streets with clear sight distance ≥ 150 m (plain/rolling terrain).
• In hilly terrain, sight distance depends on design speed.
• Front panel must not be used for advertising.

2. VMS Design Process (Clause 22.2)

• Step a: Data Collection
  • Intended purpose of VMS
  • Type of information to display
  • Alternative route diversion points
• Step b: Determine VMS Type
  • Based on purpose and information type
  • Select appropriate VMS technology (e.g., LED, flip-dot)
• Step c: Corridor Placement
  • Choose locations ensuring visibility and relevance to traffic flow

3. Additional Specifications

• VMS controller (Clause 11.4) must be reliable for message management.
• Ensure adequate legibility time based on vehicle speed and sight distance.

Example Formula for Minimum Legibility Distance

[ \text{Legibility Distance} = \text{Design Speed (km/h)} \times 3.6 \times \text{Legibility Time (s)} ]

Where legibility time is typically 4-6 seconds.

Summary Table: VMS Placement Criteria

flowchart TD
    A[Start: VMS Need Assessment] --> B[Collect Data]
    B --> C[Determine VMS Type]
    C --> D[Select Placement Location]
    D --> E[Design & Controller Setup]
    E --> F[Deployment & Monitoring]

This concise approach ensures effective VMS design aligned with IRC SP 85 guidelines.

VMS Matrix Displays (IRC SP 85: Clause 22.1 & related clauses)

Matrix Types

• Character Matrix: Separate space per character (e.g., 8x3 = 24 characters). Not recommended.
• Line Matrix: Characters in a line without separation; lines separated. Recommended.
• Full Matrix: No separation between characters or lines; flexible message size/location. Recommended.

LED Pixel Specifications (Clause 11.2.1)

• Pixel Size: 15 to 22 mm
• Pixel Pitch: 22 to 25 mm (center-to-center distance)
• LEDs grouped per pixel to meet luminance requirements.

Controller & Communication (Clauses 11.4.3, 12)

• Monitors display and controls LEDs.
• Supports communication protocols: NTCIP, Ethernet (UDP/IP), RS-232.
• Unique addressable units for remote control and diagnostics.

Power & Protection (Clauses 17, 13)

• Power: 230 V AC, 50 Hz, with 6-hour inverter backup.
• Surge protection with arresters; earthing resistance ≤ 3Ω.

Storage & Messaging (Clauses 14, 19)

• Stores minimum 20 frames locally.
• Central control can schedule/display sequences (min 10 messages).
• Logs message ID, content, and display timestamps.

Structural & Environmental (Clause 20)

• Housing: Powder coated, IP55 protection.
• Mounting structure withstands wind speeds up to 200 km/h.
• EMI protection for electronics.

Summary Table: VMS Pixel Dimensions

flowchart LR
    A[Message Input] --> B[VMS Controller]
    B --> C[LED Pixels (Matrix Display)]
    C --> D[Display Message]
    B --> E[Health Status Monitoring]
    B --> F[Central Control Computer]
    F --> B

This diagram shows the message flow and control feedback loop.

For detailed design,

Key Specifications for Mounting Structures and Housing (IRC SP 85):

Mounting Structure (Clause 5.5 & 10.9.3)

• Pole:
  • Height: Minimum 5.5 m
  • Shape: Hexagonal/Octagonal MS pole
  • Diameter: Minimum 300 mm
  • Thickness: Minimum 5 mm
• Base Plate:
  • Size: Minimum 520 mm x 520 mm x 16 mm
  • With sufficient stiffeners and support angles
• Finish:
  • One coat primer + two coats PU paint
• Wind Load:
  • Designed for wind speeds up to 150 km/h
• Clearance:
  • Minimum vertical clearance under sign: 5.5 m

Housing (Clause 10.6 & 10.7)

• Material: Aluminum alloy extrusions
• Assembly:
  • Walk-in housing: Welded structural framing
  • Other types: Bolted with stainless steel/aluminum hardware
• Finish: Maintenance-free natural aluminum finish on back, top, bottom, and sides to minimize heat build-up

Structural Integrity Compliance

• Follow Standard Specifications for Structural Supports for Highway Signs, Luminaires, and Traffic Signals for load and design.

Summary Table

graph TD
A[Mounting Structure] --> B[MS Pole: 5.5 m, 300 mm dia, 5 mm thick]
A --> C[Base Plate: 520x520x16 mm with stiffeners]
A --> D[Paint: Primer + 2 PU coats]
A --> E[Wind Load: 150 km/h]
F[Housing] --> G[Material: Aluminum alloy extrusions]
F --> H[

IRC SP 85 - Access and Maintenance Key Points

1. Access Panels (Clause 10.9)

• Panels limited in size for one-person operation.
• Gasketed & sealed against weather ingress.
• Lockable to prevent unauthorized access.
• Supported by multiple self-locking devices to hold open at wind speeds up to 64 km/h.

2. Walk-in Access (Clause 10.9.1)

• Walkways along support structure mandatory.
• Minimum aisle width inside housing: 61 cm (24 inches).
• Non-skid aluminum floor required.
• Doors must have handles inside & outside to prevent trapping without keys/tools.

3. Canopy Doors (Clause 10.9.2)

• For signs > 183 cm height, doors hinged top & intermediate points.
• Open doors create temporary shelter (roof + partial rear wall).
• Gap between adjacent doors ≤ 19 mm (3/4 inch).
• Doors allow immediate access without removing parts or tools.
• Manufacturer to provide catwalks, framing, and diamond-etched solid floors over live traffic.

Summary Table

flowchart LR
    A[Access Panels] --> B{Size}
    B -->|One person operable| C[Lockable & Gasketed]
    C --> D[Self-locking support @ 64 km/h wind]
    A --> E[Walk-in Access]
    E --> F[Aisle width ≥ 61 cm]
    E --> G[Non-skid floor]
    E --> H[Door handles inside & outside]
    A --> I[Canopy Doors (>183 cm)]
    I --> J[Hinged top & intermediate]
    I --> K[Gap ≤ 19 mm]
    I --> L[Temporary shelter when open]
    I --> M[Catwalks & solid floor over traffic]

This ensures safe, weather-protected, and efficient maintenance access per

Key Specifications & Interfaces for Communication and Control (IRC SP 85)

1. VMS Controller Communication:

• Unique addressability from Control Centre.
• Supported protocols:
  • PMPP - NULL
  • PPP - NULL
  • Ethernet - UDP/IP
  • RS-232
• Supports NTCIP or equivalent international protocols.

2. Data Communication:

• Communication links: Dedicated line, Leased line, GSM/CDMA (DATA/SMS channels).
• Security: Must have sufficient security checks to prevent unauthorized access.

3. Controller Functions:

• Continuous self-monitoring of display.
• Commands LEDs on/off to display messages.
• Accumulates status data for transmission.
• Receives commands from Central and Portable Maintenance Computers.

4. Data Storage:

• Minimum storage of 20 frames for display.
• Messages can be triggered remotely.

5. Central Control Computer:

• Controls individual or groups of VMS.
• Can schedule messages with date/time.
• Stores message logs with:
  • VMS ID
  • Message content/number
  • Start & end time of display
• Performs regular exhaustive VMS tests.

6. Power & Protection:

• Power supply: 230 V AC, 50 Hz single phase.
• Backup: Inverter with 6-hour backup.
• Surge protection & earthing ≤ 3 Ohms.

7. Portable VMS Controller:

• 19-inch rack mounted, 32-bit CPU @ ≥400 MHz.
• 20 MB SRAM + expandable 16 MB FLASH.
• Battery operation at 12V DC with charging.
• Integrated Digital I/O board (4 inputs, 4 outputs).
• Local TFT color screen with keypad for diagnostics.

Summary Table: Communication Protocols & Interfaces

flowchart LR
    Central_Control_Computer -->|Commands| VMS_Controller
    VMS_Controller -->|Status Data| Central_Control_Computer
    VMS_Controller

IRC SP 85 – Operational Guidelines (Part-A)

The Operational Guidelines in IRC SP 85 focus on the use and management of Variable Message Signs (VMS) on highways. Key points include:

1. Principles (Clause 3)

• VMS should enhance road safety and traffic management.
• Messages must be clear, concise, and timely.

2. Purpose of VMS (Clause 4)

• Inform drivers about road conditions, hazards, diversions.
• Manage traffic flow during incidents or peak hours.

3. When to Use a VMS (Clause 5)

• During accidents, roadworks, adverse weather, or special events.
• To provide real-time information affecting driver decisions.

4. Message Content (Clause 6)

• Use standardized symbols and text.
• Limit message length for quick comprehension.
• Prioritize critical safety info.

5. Display (Clause 7)

• Ensure visibility under various lighting/weather.
• Use appropriate font size and color contrast.

6. Special Cases

• Urban Areas (Clause 8): Adjust message complexity and frequency.
• Portable VMS (Clause 9): For temporary or mobile deployments.

Summary Table: VMS Operational Aspects

flowchart TD
    A[Traffic Event] --> B{Is VMS Needed?}
    B -- Yes --> C[Select Message Content]
    C --> D[Display on VMS]
    D --> E[Driver Receives Info]
    B -- No --> F[No Action]

For detailed formulas or technical specs, refer to Part-B of IRC SP 85.

Safety and Traffic Flow Considerations (IRC SP 85)

Key Specifications:

• Minimum Distance for VMS Placement:

  • Expressways: ≥ 1.5 km before diversion/access point
  • National Highways (NH): ≥ 1 km before diversion/access point

• Alignment Requirements:

  • Horizontal: VMS must be on tangent sections for clear visibility.
  • Vertical: Ideal grades ≤ 1%; avoid grades > 4%.

• Sign Spacing:

  • Expressways: Minimum 250 m between VMS and other signs.
  • NH: Minimum 150 m spacing.

• Power and Infrastructure:

  • Ensure power source availability along the segment.
  • Consider underground infrastructure, conduit routing, and cabinet placement.

Traffic Flow Messaging:

• Use VMS for advance warning of lane closures, accidents, construction, and special events.
• Display messages within a week of the event.
• In urban areas, restrict VMS messages to through routes and high-speed corridors.

Typical Safety Messages (Annex-B Extract)

Summary Flow for VMS Site Selection

flowchart TD
    A[Collect Site Data] --> B[Assess Horizontal & Vertical Alignment]
    B --> C[Check Existing Signs & Spacing]
    C --> D[Evaluate Power & Infrastructure]
    D --> E[Select VMS Location & Height]
    E --> F[Determine Cabinet & Conduit Layout]
    F --> G[Finalize Communications Medium]
    G --> H[Iterate Design if Needed]

References: IRC SP 85 Clauses 1.5, Annex-A & B, Clause 5.4.

IRC SP 85 Annexures & References Summary

Key Specifications & Tables:

VMS Design Process (Clause 1.5)

• Minimum Distance for VMS Placement:
  • Expressway: ≥ 1.5 km before access point
  • National Highway (NH): ≥ 1 km before access point
• Site Selection Criteria:
  • Tangent road sections for clear visibility
  • Road grade ≤ 1% ideal; avoid >4%
  • Distance from existing signs: Expressway ≥ 250 m, NH ≥ 150 m
  • Power source location consideration
• Design Considerations:
  • VMS supports, height, cabinet placement
  • Underground infrastructure & conduit routing
  • Communication medium selection
  • Iterative design refinement

Annex-B: Typical VMS Messages (Clause 6.4)

• Standardized messages for closures, lane restrictions, accidents, construction, weather, and traffic conditions.
• Examples:
  • "ACCIDENT AHEAD ROAD CLOSED"
  • "LEFT LANE CLOSED AHEAD"
  • "HEAVY TRAFFIC AHEAD"
  • "FOGGY CONDITIONS MAY EXIST"
  • "RUNAWAY TRUCK RAMP OCCUPIED"

Abbreviations

• VMS: Variable Message Sign
• CMS: Changeable Message Sign
• DMS: Dynamic Message Sign
• LED: Light Emitting Diode

Summary Diagram: VMS Site Selection Process

flowchart TD
    A[Collect Site Data] --> B[Analyze Horizontal & Vertical Alignment]
    B --> C[Check Existing Signs & Power Source]
    C --> D[Select VMS Location]
    D --> E[Design Supports & Cabinet Placement]
    E --> F[Plan Underground Infrastructure]
    F --> G[Determine Communication Medium]
    G --> H{Design Complete?}
    H -- No --> A
    H -- Yes --> I[Finalize Design]

Use IRC SP 85 Annexures for standardized messages and detailed VMS siting/design guidelines to ensure safety and operational efficiency on highways.