IRC Code 102: Conducting Traffic Studies for Bypass Planning – Methodologies and Best Practices

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In the era of rapid urbanization and increasing vehicular movement, traffic congestion within town limits has become a pressing issue. One of the most effective solutions to mitigate this challenge is the construction of bypasses. To ensure these bypasses are well-planned and serve their intended purpose, IRC Code 102:1988, issued by the Indian Roads Congress (IRC), provides a systematic approach for conducting traffic studies for bypass planning.

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In this blog, we delve into the methodologies, practices, and significance outlined in IRC Code 102 for bypass planning, offering a detailed, easy-to-understand guide for engineers, planners, and stakeholders involved in transportation infrastructure.

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1. Introduction to IRC Code 102:1988

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IRC Code 102:1988 was developed by the Traffic Engineering Committee of the Indian Roads Congress with a clear objective: to provide detailed guidelines for conducting traffic studies that justify and shape the development of bypasses around towns.

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The key purpose is to:

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• Alleviate congestion within urban areas

• Ensure smooth movement of through traffic

• Prevent deterioration of urban traffic environments

• Promote long-term functional viability of bypasses

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The code emphasizes the importance of aligning bypasses with the town’s master plan and controlling ribbon development through legislation and planning.

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2. Scope of Traffic Studies for Bypass Planning

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The traffic study focuses on identifying and analyzing the type and volume of traffic, particularly distinguishing between:

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• External to External Traffic (through traffic)

• External to Internal Traffic

• Internal to External Traffic

• Internal Traffic

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Only external-to-external traffic is fully bypassable. Other types may still enter the town for basic services, which can be relocated to the bypass itself to ensure diversion.

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The study also examines origin-destination patterns, traffic volume, route characteristics, and delay data, forming the basis for deciding bypass alignment and infrastructure needs.

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3. Methodologies for Traffic Data Collection

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3.1 Origin-Destination (O-D) Surveys

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These surveys are essential to determine the volume and nature of through traffic. They involve:

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• Location of Cordon Line: Positioned beyond urban influence to capture bypassable traffic

• Simultaneous Surveys: Conducted across all entry and exit points

• Survey Duration: Minimum of 3 days, ideally 7, including market and working days

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Sampling Requirements:

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• 25% coverage during peak periods

• 50% during normal periods

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Data Collection Techniques:

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• Registration Plate Method: Records vehicle numbers and timestamps without interaction

• Tag and Disc Method: Attaches tags or discs at entry and collects them at exit

• Roadside Interview Method: Involves direct interviews for detailed origin-destination data

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3.2 Traffic Volume Counts

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These counts are taken in 15-minute intervals using standard proformas to help extrapolate O-D data to the total traffic volume.

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3.3 Travel Time and Delay Studies

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Moving car techniques are used to determine delays along proposed routes:

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• Floating Car Method
• Average Car Method
• Restricted Car Method

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These help measure the time lost due to congestion and delays across different sections of the route.

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4. Data Analysis and Evaluation

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4.1 Traffic Volume Analysis

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Volume data is tabulated to identify peak hours and total flow using Form 4 provided in the code.

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4.2 Delay Analysis

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Average delays are calculated from multiple test runs (preferably six) using Form 5.

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4.3 Speed-Flow Relationship

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Speed and flow are correlated to assess Level of Service (LOS) using the formula:

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Vest=Vf−kQV_{est} = V_f - kQVest​=Vf​−kQ

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Where:

• VestV_{est}Vest​: Estimated speed
• VfV_fVf​: Free flow speed
• QQQ: Traffic volume
• kkk: Coefficient

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4.4 Origin-Destination Matrix

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A matrix is created to show vehicle movement between all cordon points, and to compute the percentage of through traffic, which is crucial in determining the need for a bypass.

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4.5 Estimation of Losses

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Using Form 10 and 11, the analysis includes:

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• Loss of man-hours due to delays

• Additional fuel consumption

• Economic loss in monetary terms

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5. Future Traffic Projections

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To justify a bypass in economic and operational terms, 20-year projections are considered based on:

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• Population growth
• Regional development
• Vehicle registration data

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Form 12 is used to calculate the compounded economic losses if a bypass is not constructed, thus reinforcing the long-term value of investment.

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6. Economic Analysis

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By comparing the anticipated economic loss (due to continued congestion) and the investment in a bypass, planners can determine the cost-benefit ratio. The analysis must also include:

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• Accident reduction savings
• Improved traffic flow
• Environmental benefits

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7. Presentation of Findings

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The code recommends using desire-line diagrams and tabulated summaries to visualize:

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• Direction and volume of bypassable traffic

• Potential bypass alignments

• Strategic control points for interventions

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These diagrams simplify complex data, making it actionable for decision-makers.

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8. A Hypothetical Case Study Example

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IRC 102 provides a detailed example case study that walks through:

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• O-D matrix formation

• Sectional traffic computations

• Hourly traffic and delay summaries

• Speed and travel time analysis

• Economic loss estimations (man-hours and fuel)

• Justification for a bypass based on projected savings

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This practical demonstration helps engineers understand how to apply the guidelines in real-world scenarios.

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Conclusion

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Bypass planning is a critical strategy to enhance urban mobility and reduce congestion. IRC Code 102:1988 offers a rigorous, data-driven methodology for conducting traffic studies that support such planning. From precise survey techniques to advanced economic evaluations, the code ensures that each bypass project is technically sound, economically justified, and future-ready.

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For transportation professionals and urban planners, adhering to these guidelines is essential to create sustainable, effective road infrastructure solutions.

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FAQs

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Q1. Why are traffic studies important for bypass planning?

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They help assess traffic load, route effectiveness, and design feasibility.

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Q2. What methods are commonly used?

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Origin-destination surveys, turning counts, and simulation models.

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Q3. How does IRC Code 102 guide these studies?

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IRC Code 102 prescribes methodology and criteria for accurate results.

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