IRC 87 : 2018Guidelines for Planning and Design of Interchanges for National Highways

IRC 87 specifies guidelines for planning and design of interchanges for national highways — grade-separated junctions where two or more roads cross at different levels with ramp connections enabling traffic to transfer between them. Interchanges are the standard junction type on access-controlled highways (NH-A, expressway) and at major intersections in tier-1 / tier-2 urban areas.

Use IRC 87 when designing: - New expressway / access-controlled highway interchange - Upgrade of at-grade major intersection to grade-separated - Highway-to-highway interchange (NHAI golden quadrilateral, Bharatmala corridors) - Highway-to-arterial interchange (NH meets state highway / city ring road) - Bus terminal / truck terminal access from highway - Toll plaza approach interchange

Interchange design is one of the most complex highway-engineering tasks: it integrates traffic capacity, geometric design, pavement design, drainage, structures, lighting, signage, safety, land acquisition, environmental impact, and cost optimisation across a multi-year construction project costing tens-to-hundreds of crores.

IRC 87:2018 is the latest comprehensive update; previous editions (2003) had less coverage of urban-context constraints and modern smart-junction design.

1. Diamond Interchange: - Simplest — four ramps form a diamond around the major road - Major road grade-separated from minor road; minor road ramps connect at-grade - Best for: minor road has low traffic, land available for ramps, signalised ramp intersections OK - Capacity: limited by ramp-intersection signalisation

2. Cloverleaf: - Four loop ramps within four quadrants, weaving between major roads - All movements grade-separated, no signal - Best for: equal traffic on both major roads, large land available - Capacity: limited by short weaving distance between loop entries / exits - Modern variant: 'parclo' (partial cloverleaf) reduces land

3. Trumpet Interchange: - T-junction where one road ends at another grade-separated - Three ramps + one loop - Best for: terminal interchange, toll plaza access, T-shaped traffic pattern - Capacity: high; standard for highway-end toll booths

4. Directional / Stack Interchange: - All movements via direct ramps (not loops); multiple-level stack of bridges - 4 to 5 levels possible - Best for: very high-volume crossings of two expressways; downtown limited land - Capacity: highest; cost: highest (often ₹500-1000+ crore) - Examples: Dwarka-Gurgaon expressway, Mumbai BKC interchange

5. Single-Point / Single Point Urban Interchange (SPUI): - Compact diamond with single signal serving all ramps - Best for: urban dense areas, limited right-of-way - Capacity: medium; relies on efficient signal phasing

Ramp design speed (Clause 6.2):

| Major road design speed | Ramp design speed | |---|---| | 100 km/h (NH) | 60-80 km/h | | 80 km/h | 50-65 km/h | | 60 km/h (urban) | 40-50 km/h |

Ramp horizontal radius: - Loop ramp (cloverleaf): 50-75 m (low speed, < 40 km/h) - Directional ramp: 200-500 m (higher speed) - Ramp transition spirals at entry / exit

Ramp gradient: - Maximum: 4-5 % (for 80 km/h ramp); 3 % for high-speed direct ramps - Vertical curve K values per design speed (per IRC SP 23:2012)

Ramp width (Clause 7): - Single-lane ramp: 5.0 m carriageway (3.75 m lane + 1.25 m shoulder) - Two-lane ramp: 8.0 m carriageway (2 × 3.5 m + 0.5 m + 0.5 m shoulders)

Acceleration / deceleration lane lengths (per IRC 87):

| Highway speed (km/h) | Acceleration (m) | Deceleration (m) | |---|---|---| | 80 | 200-250 | 150-180 | | 100 | 280-330 | 200-240 | | 120 | 350-400 | 250-300 |

Minimum vertical clearance: - Major road over minor / ramp: 5.5 m (for through-traffic + truck clearance) - For pedestrian / utility under road: 5.0 m

Sight distances: - Stopping sight distance per IRC:66:1976 / IRC SP 23:2012 - Decision sight distance at exit ramp gore: 1.5-2 × SSD (driver needs to spot, decide, decelerate) - Passing sight distance: rarely controls on interchanges

Lane drop / lane gain points: - Lane drop at ramp exit: smooth taper 1:30 to 1:50 (depending on speed) - Lane gain at ramp entry: 1:30 to 1:50 taper - Always provide auxiliary lane / weave area between consecutive ramps

Right-of-way (typical): - Diamond: 100-200 m × 150-300 m (~3-6 acres) - Cloverleaf: 300-500 m × 300-500 m (~25-50 acres) - Stack interchange: 400-600 m × 400-600 m (~50-100+ acres)

• IRC:73:1980 — geometric design standards for rural highways (parent geometric code).
• IRC SP 23:2012 — design of vertical curves (heavily used on ramp profiles).
• IRC:38:1988 — design of horizontal curves (ramp curves).
• IRC:66:1976 — sight distance on rural highways (SSD, OSD, ISD).
• IRC:64:2017 — capacity of roads in rural areas (interchange weave-and-merge analysis).
• IRC SP 41:2005 — at-grade intersections (alternative to interchange where volume permits).
• IRC:5:2015 — bridge design (interchange overpass / underpass structures).
• IRC:6:2017 — loads and load combinations for bridges.
• IRC:78:2014 — foundations and substructures for bridges.
• IRC:21:2000 — concrete bridge design (typical interchange overpass).
• IRC:22:2008 — composite construction.
• IRC:24:2010 — steel road bridges.
• IRC:99:2018 — vehicular barriers (relevant on ramps and bridges).
• IRC:35:2015 — code of practice for road markings.
• IRC:67:2012 — code of practice for road signs.
• IRC:112:2020 — code of practice for concrete road bridges.
• IRC:37:2018 — flexible pavement design.
• IRC:58:2015 — rigid pavement design.
• AASHTO 'A Policy on Geometric Design of Highways and Streets' — international reference (often cited for advanced interchange topics).

1. Inadequate weaving distance between consecutive ramps. If two ramps are close together (e.g., entry then exit), drivers cannot complete lane changes. Provide at least 200-300 m weaving section depending on speed. 2. Loop ramp radius too tight. Loop radii < 50 m force drivers to brake from highway speed to crawling speed in a short distance — accident-prone. Either increase radius or use directional ramp instead of loop. 3. Acceleration lane too short. Drivers entering highway from short ramp cannot reach highway speed; force-merge causes rear-end collisions. Stick to IRC 87 acceleration-lane lengths per highway speed. 4. Inadequate signage at ramp gore. Drivers miss exit, take wrong ramp, dangerous reverse / U-turn maneuvers. Multiple advance signs (1 km, 500 m, 200 m) per IRC:67. 5. Vertical alignment too steep on ramps. > 5 % gradient causes truck speed loss → traffic backup. Specify ≤ 4 % on heavily-trafficked ramps; design vehicle climbing-lane on long upgrades. 6. No provision for two-wheelers / non-motorised traffic. Indian context: two-wheelers form 30-50 % of traffic. Need separate two-wheeler ramp / service road, especially in urban interchanges. 7. Drainage failure on ramps. Ramps with curves + grades trap water at low points; aquaplaning hazard. Drain to outside-of-curve, slope > 0.5 %. 8. Bridge structure not designed for actual traffic. Highway bridges per IRC:6:2017 Class A; many older interchange bridges underdesigned for current axle loads. Verify bridge loading on existing-bridge upgrade. 9. Toll plaza too close to interchange exit. Vehicles stopping at toll back up onto exit ramp; secondary collision hazard. Place toll 500 m+ downstream of exit gore. 10. No consideration for emergency / breakdown vehicle. Provide breakdown bays / emergency ramps / staging areas for emergency vehicles within / near interchange. 11. Land acquisition under-budgeted. Stack interchanges need 50+ acres; cloverleaf 25+. Land acquisition often exceeds 30 % of project cost; under-estimating it causes cost overrun and project delay. 12. Lighting + traffic management neglected. High-speed merging at night is most accident-prone time; specify high-mast lighting, retroreflective signage, signal-controlled merging where appropriate.

Interchange project lifecycle:

1. Need study — traffic O-D survey, projected volumes, accident analysis at existing junction, capacity gap. 2. Alternative analysis — evaluate at-grade upgrade (IRC SP 41) vs interchange types; cost-benefit, traffic, safety analysis. 3. Type selection — diamond / cloverleaf / trumpet / stack / SPUI per traffic volume, available land, cost. 4. Preliminary design — alignment, ramp configuration, structure types, footprint. 5. Detailed design: - Geometric: ramp radii, gradients, transitions (IRC SP 23, IRC:38) - Structural: bridges and ramps (IRC:5, IRC:6, IRC:21, IRC:22, IRC:78) - Pavement: rigid for ramps + at junction throats (IRC:58); flexible for less-trafficked sections - Drainage: surface + cross-drainage - Lighting + signage + barriers + markings 6. Land acquisition + permits — environmental clearance, R-O-W acquisition. 7. Tendering + construction — typically 24-48 months for major interchange. 8. Operations + maintenance — toll collection (if applicable), routine inspection, post-construction traffic monitoring (validates capacity assumptions).

Typical project cost ranges: - Diamond interchange: ₹50-150 crore - Cloverleaf: ₹200-500 crore - Stack interchange: ₹500-2000+ crore - Above plus land acquisition (often 30-50 % of total)

IRC 87 is the geometric design backbone; structural design draws on the other IRC bridge codes; together they enable design of safe, high-capacity grade-separated junctions.