Understanding the IRC Code: Guidelines for Traffic Forecasting on Highways

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The Indian Roads Congress (IRC) has established a vital framework for traffic forecasting on highways through its IRC Code 108-2015. This code serves as an essential guide for traffic engineers and planners, providing structured methodologies for predicting traffic volumes on highways and inter-urban roads. In this blog, we will explore the key components of the IRC Code, its significance, and how it aids in the effective planning and management of highway infrastructure.

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The Importance of Traffic Forecasting

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Traffic forecasting is a critical aspect of road and highway projects. Accurate traffic volume predictions are necessary for evaluating the feasibility and design of road facilities. The IRC Code emphasizes that all road projects require a solid understanding of future traffic volumes to ensure that the infrastructure can accommodate expected growth. This is particularly important for assessing the economic and financial viability of projects, as traffic forecasts directly influence funding and resource allocation.

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Basic Concepts of Traffic Forecasting

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The IRC Code outlines several fundamental concepts and terminologies essential for traffic forecasting:

• Average Daily Traffic (ADT): The total volume of traffic passing a point over a specified period, averaged over the number of days.
• Annual Average Daily Traffic (AADT): The total volume of traffic over a year, averaged daily.
• Design Hourly Volume (DHV): The hourly volume used to assess capacity requirements, typically taken as the 30th highest hourly volume in a year.
• Forecast Period: The time span covered by the traffic forecast, which is crucial for long-term planning.

These definitions provide a foundation for understanding the methodologies used in traffic forecasting.

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Methodological Aspects of Traffic Forecasting

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Stages of Traffic Forecasting

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The IRC Code outlines a systematic approach to traffic forecasting, divided into three main stages:

1. Preparatory Works: This stage involves understanding the proposed project corridor and its role in regional development. It includes reconnaissance surveys and the identification of the Project Influence Area (PIA) and Traffic Analysis Zones (TAZs).
2. Analysis of Base Year Travel: This stage focuses on collecting and analyzing primary and secondary data to establish base year traffic estimates. Primary traffic surveys, such as mid-block volume counts and origin-destination surveys, are conducted to gather relevant data.
3. Forecasting Travel Demand: In this final stage, traffic forecasts are generated based on the analysis of base year data and the application of growth factors. The forecast considers normal traffic, generated traffic, and developmental traffic, providing a comprehensive view of future traffic volumes.

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Components of Traffic Forecast

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The IRC Code emphasizes the need to estimate various components of traffic:

• Normal Traffic: This is the expected traffic due to population growth and socio-economic development in the region.
• Generated Traffic: This includes traffic attracted to the project corridor due to improvements in road conditions, which can be further divided into diverted and induced traffic.
• Developmental Traffic: This refers to additional traffic resulting from significant land-use changes in the PIA, such as new residential or commercial developments.

By considering these components, traffic engineers can create more accurate and realistic traffic forecasts.

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Practical Applications of the IRC Code

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The IRC Code provides several example problems and methodologies that traffic engineers can adopt for specific projects. These examples illustrate how to apply the guidelines in real-world scenarios, ensuring that traffic forecasts are both practical and scientifically grounded.

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Impact of Toll on Traffic Volume

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One of the critical considerations in traffic forecasting is the impact of tolls on traffic volume. The IRC Code highlights that toll charges can deter traffic growth, especially when competing routes are available. Therefore, it is essential to factor in the effects of tolls when estimating future traffic volumes on toll roads.

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Highways Passing Through Urban Areas

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When highways pass through urban or suburban areas, the traffic dynamics change significantly. The IRC Code advises that separate forecasts should be conducted for local, regional, and through traffic to accurately capture the complexities of urban traffic patterns.

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Conclusion

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The IRC Code 108-2015 serves as a comprehensive guide for traffic forecasting on highways, equipping traffic engineers and planners with the necessary tools to make informed decisions. By understanding existing traffic flows, estimating growth, and considering various influencing factors, stakeholders can design and manage highways that meet current and future demands effectively.

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