Pradhan Mantri Gram Sadak Yojana — India’s flagship rural road programme connecting unconnected habitations with population >500 (>250 in hilly/tribal areas). Over 6 lakh km built. All roads designed per IRC SP:20 and IRC 73. World’s largest rural road building programme.

Single lane: 3.75m carriageway + 0.5m shoulders = 4.75m total (per IRC 73). Two lane: 7.0m + 1.5m shoulders = 10.0m. Most PMGSY roads are single lane with passing places every 200-300m.

Depends on traffic and drainage: Gravel/WBM for <150 CVPD with good drainage. Bituminous surface (SDBC 25mm or PC+seal coat) for 150-450 CVPD. Cement concrete per IRC SP:62 for waterlogged areas or black cotton soil. Concrete lasts longer but costs more.

Poor drainage — water entering the pavement structure causes softening and failure. IRC SP:20 Chapter 6 covers drainage design in detail. Second cause: inadequate compaction during construction. Third: overloaded vehicles beyond design capacity.

Per IRC SP:20 Chapter 6: 1) Estimate catchment area from toposheet, 2) Calculate peak runoff using Rational Method Q=CIA/360, 3) Select pipe/slab culvert size from Table 6.1, 4) Minimum pipe dia 600mm (to prevent choking). For streams >3m wide, consider slab or box culvert.

The primary difference lies in the design traffic, design speed, and the level of geometric and pavement design. Village roads are typically designed for lower traffic volumes and lower speeds (30 kmph), often with simpler pavement structures like earthen or gravel. District roads, carrying more traffic, demand higher design speeds (50 kmph) and more robust pavement designs, potentially including WBM or bituminous surfaces.

IRC SP 20:2002 emphasizes the importance of subgrade evaluation, even for rural roads. The California Bearing Ratio (CBR) is the primary parameter used. For low-volume roads, a minimum CBR of 2% is often assumed for design purposes, but actual testing is recommended. The design pavement thickness is directly influenced by the subgrade CBR value, with higher CBR requiring thinner pavements.

Drainage for rural roads primarily involves surface drainage. This includes appropriate camber to quickly shed rainwater off the pavement, well-designed side drains (earthen, lined, or rubble masonry depending on flow velocity and soil type), and culverts or minor bridges for cross-drainage. Proper grading of shoulders and side slopes is crucial to direct water away from the pavement.

While IRC SP 20:2002 focuses more on the structural design, it implicitly addresses dust by advocating for proper compaction and surface treatments. For unpaved roads, best practices often involve periodic grading, application of waste materials (like quarry dust or certain industrial by-products where appropriate), or controlled sprinkling of water during dry spells, though the latter is less sustainable.

The manual strongly advocates for the use of locally available materials to reduce costs and enhance sustainability. It also implicitly supports community participation by suggesting designs that are manageable and maintainable by local bodies. This often involves selecting construction techniques and materials that local labor can handle effectively, aligning with programs like PMGSY.

The code provides specifications for various pavement layers like Granular Sub-base (GSB), Wet Mix Macadam (WBM), and bituminous surfaces. It outlines requirements for aggregate properties, gradation, and quality control tests. For bituminous roads, it also touches upon binder grades suitable for local climatic conditions, considering maximum pavement temperatures.

IRC SP 20:2002 provides guidance on the design and construction of culverts and small bridges. Key considerations include hydraulic design to pass expected flood discharges without causing upstream flooding, appropriate waterway opening size, structural design for anticipated loads, and protection against scour. The type of structure (box culvert, pipe culvert, slab culvert) depends on the span and site conditions.

The code emphasizes that maintenance is an integral part of the road lifecycle. It suggests a regime of routine maintenance, including clearing drains, repairing potholes, and maintaining shoulders. Periodic maintenance, such as re-gravelling or resurfacing, is also covered. Regular inspections are crucial to identify and address minor issues before they escalate.

For rural roads located in mountainous or steep terrain, IRC SP 20:2002 recommends a design speed of 30 kmph. This lower speed is primarily due to the presence of sharp curves, steep gradients, and reduced visibility. Adhering to this design speed ensures adequate stopping sight distance and lateral acceleration control for safe operation.

A subgrade CBR of 2% represents a poor-quality soil. According to IRC SP 20:2002, such a low CBR necessitates a significant pavement thickness to distribute traffic loads effectively. This usually translates to a substantial granular sub-base and base layer, which adds to the construction cost but is essential for pavement stability and longevity.

IRC SP 20:2002 specifies minimum carriageway widths based on the road classification and intended use. For single-lane rural roads, a minimum of 3.0 m for earthen/gravel and 3.75 m for WBM/bituminous surfaces is typically recommended. Two-lane roads generally require a minimum of 7.0 m. Intermediate lane widths of 2.45 m per lane are also provided for specific applications.

Quality control as per IRC SP 20:2002 involves ensuring that materials meet specifications and that construction methods are followed correctly. This includes field tests for soil compaction, aggregate gradation, moisture content, and density. Regular inspections by site engineers and quality assurance personnel are vital to prevent defects and ensure the durability of the constructed road.