A Comprehensive Guide to IRC Code 106:1990 – Guidelines for Capacity of Urban Roads

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The IRC Code 106:1990, published by the Indian Roads Congress, lays down essential guidelines for determining the capacity of urban roads. This document provides a framework to evaluate traffic flow, establish levels of service (LOS), and ensure effective urban traffic management. With urbanization accelerating, the principles in this code are vital for planners and engineers to create efficient road networks.

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Understanding IRC Code 106:1990

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The primary objective of IRC Code 106:1990 is to assist in determining the capacity of urban roads under varying traffic conditions. The code defines Capacity as the maximum sustainable hourly rate at which vehicles can traverse a given point or segment of a road during peak conditions. It emphasizes the role of urban-specific factors such as mixed traffic flow, pedestrian volume, and roadside activities, which distinguish urban road capacity from that of rural roads.

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Levels of Service (LOS)

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The code introduces the concept of Levels of Service (LOS) to describe operational conditions and the quality of traffic flow. LOS is categorized into six levels (A to F), which range from free flow to forced or breakdown conditions. Here's a breakdown of the levels:

Level of Service A: Free Flow

• Characteristics: Maximum comfort and convenience, with travel speeds around 90% of free-flow speeds.
• Traffic Interaction: Minimal, with drivers having complete freedom to maneuver.

Level of Service B: Stable Flow

• Characteristics: Average speeds drop to 70% of free-flow speeds.
• Traffic Interaction: Drivers experience some restrictions due to increasing vehicle presence.

Level of Service C: Approaching Stable Flow

• Characteristics: Speeds reduce further to 50% of free-flow speeds.
• Traffic Interaction: Noticeable decline in comfort, with more vigilance required for maneuvering.

Level of Service D: Unstable Flow

• Characteristics: High-density traffic with speeds at 40% of free-flow speeds.
• Traffic Interaction: Limited freedom to maneuver, with discomfort increasing significantly.

Level of Service E: Capacity Flow

• Characteristics: Traffic reaches its maximum capacity; speeds fall to one-third of free-flow speeds.
• Traffic Interaction: Minor disturbances can lead to operational problems and driver frustration.

Level of Service F: Breakdown Flow

• Characteristics: Traffic exceeds capacity, resulting in queues, stop-and-go waves, and significant delays.
• Traffic Interaction: Speeds drop to 25–33% of free-flow speeds.

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Key Factors Influencing Urban Road Capacity

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The IRC Code identifies various factors that impact urban road capacity:

1. Road Characteristics: Lane width, number of lanes, and road alignment.
2. Traffic Composition: Proportion of heavy vehicles, two-wheelers, and non-motorized traffic.
3. Environmental Factors: Presence of intersections, pedestrian crossings, and roadside activities.
4. Driver Behavior: Adherence to traffic rules and reaction times.

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Application of the Code

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Engineers and urban planners can use the principles outlined in IRC Code 106:1990 to:

• Design efficient road networks that accommodate current and future traffic demands.
• Identify bottlenecks and propose measures to improve traffic flow.
• Develop sustainable traffic management systems by evaluating LOS and making data-driven decisions.

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Benefits of Following IRC Code 106:1990

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1. Improved Traffic Management: Enables better planning of urban road networks.
2. Enhanced Road Safety: Reduces the likelihood of accidents by maintaining optimal traffic flow.
3. Increased Commuter Comfort: Ensures smoother travel experiences for road users.

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Conclusion

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The IRC Code 106:1990 is a critical resource for managing the complexities of urban traffic. By implementing its guidelines, urban planners and engineers can optimize road capacity, improve levels of service, and create roadways that cater to the needs of a growing urban population.

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