IRC 5:2015 is the Indian Standard (IRC) for standard specifications and code of practice for road bridges — general features of design. IRC 5 covers the general layout and features of road bridges — carriageway width, vertical clearance, footpaths, railings, drainage, and overall arrangement. This is the starting point for any bridge design — sets the geometric framework before structural design begins.
General design requirements for road bridges including classification, roadway width, vertical clearance, footpath, railing, drainage, and general arrangement.
Carriageway widths, classification, free-board, clearances and umbrella references for road bridges.
| Reference | Value | Clause |
|---|---|---|
| Bridge classification — by span | Culvert ≤6 m, Minor 6-30 m, Major 30-120 m, Important >120 m | |
| Carriageway width — 2-lane single carriageway (kerb-to-kerb) | 7.5 m | Cl. 103.3.1 |
| Carriageway width — 4-lane divided | 2 × 7.5 m + median | Cl. 103.3.2 |
| Footpath width on bridges — minimum— 1.0 m on minor bridges | 1.5 m (each side) | Cl. 103.6 |
| Crash barrier height (rigid concrete) — minimum | 900 mm above carriageway | |
| Pedestrian railing height — minimum | 1.1 m (1.5 m where cycles permitted) | Cl. 107.3.2 |
| Vertical clearance over highway (under bridge)— see IRC 54 for underpass details | 5.5 m (NH/SH) | Cl. 104.1.1 |
| Vertical clearance over railway | Per Indian Railways Schedule of Dimensions | Cl. 104.1.2 |
| Vertical clearance — navigable waterway HFL | Per IWAI requirements (project-specific) | Cl. 104.1.3 |
| Free board over HFL (non-navigable) — minimum— 1.5 m for major bridges | 600 mm (typical, varies by discharge) | |
| Design loads — refers | IRC 6 (Loads & Stresses) | Cl. 112.1 |
| Design discharge — return period (major bridges) | 100-year flood (typical) | Cl. 104.2.1 |
| Width of approach roads — same as bridge | Match bridge carriageway + extension 100 m each end | Cl. 108.1 |
| Min radius of curve at bridge approaches | As per IRC 73 / IRC SP 73 | Cl. 108.2 |
| Sight distance at bridge approach | SSD per IRC 66 minimum | Cl. 108.4 |
| Bearings — types covered (umbrella ref) | Elastomeric, POT, Spherical, Roller (refer IRC 83) | Cl. 111.1 |
| Expansion joint — refers | IRC SP 69 / IRC SP 72 | |
| Wearing coat — bituminous (typical) | 50 mm BC + 25 mm mastic | Cl. 111.3.2 |
| Wearing coat — concrete (PQC) on RCC deck | 75 mm M30/M40 | Cl. 111.3.1 |
IRC 5:2015 is Section I — General Features of Design of the IRC standard specifications. It is the foundational document for every road bridge designed in India, covering geometric layout, carriageway widths, clearances, kerbs, railings, expansion joint requirements, and bridge classification.
You reference IRC 5 for: - Deciding bridge carriageway width based on traffic volume and lane count - Specifying vertical clearances (over roads, railways, waterways) - Parapet and railing requirements (heights, loads, anchorage) - Footpath and cycle-track dimensions - Expansion joint types and spacing - Bridge classification by importance category
IRC 5 is the design-geometry complement to IRC 6:2017 (loads) and IRC 112:2020 (concrete design). Every bridge DPR references these three together as the design-basis trio.
Carriageway width (Clause 104): - 2-lane: 7.5 m (urban) or 7.0 m (rural) minimum - 4-lane divided: 7.5 m per direction + 1.5 m median - 6-lane divided: 11.25 m per direction + 1.5 m median - Urban expressway with 6 lanes: per MoRTH
Footpath: - Minimum 1.5 m on urban bridges - 1.0 m on rural bridges (optional if pedestrian traffic light)
Vertical clearances (Clause 105): - Over classified road: 5.5 m minimum (5.0 m for temporary) - Over railway (broad gauge): 5.5 m - Over waterway (navigable): per navigable height + 1.5 m safety - Over waterway (non-navigable): above 50-year flood + freeboard
Parapet / railing: - Height: 1.1 m minimum above finished road level - Must withstand 500 kN horizontal load per 1.5 m length (service), 1.5× factored - Design per IRC 6 Clause 215
Design task: Single-span 25 m bridge, state highway, expected 20-25 trucks per hour peak, rural setting, no footpath expected.
Per IRC 5:2015 Clause 104: - Carriageway: 7.5 m (2-lane with buses and trucks) - Kerbs on both sides: 300 mm wide × 300 mm high - Parapet: 1.1 m high (solid for rural safety) - Overall deck width: 7.5 + 2 × 0.3 + 2 × 0.15 = 8.4 m
Vertical clearance (Clause 105): Bridge spans a minor stream. 50-year flood level from hydrology study: RL 100.0 m. Freeboard: 1.0 m. Deck soffit must be ≥ 101.0 m. Bridge deck thickness: 700 mm (T-beam depth with 225 mm slab) + 65 mm wearing coat = 965 mm. Deck top level: 101.0 + 0.965 = 101.965 m. Approach road design level: match to deck, with approach slabs providing transition.
Parapet design (per IRC 6 Clause 215 + IRC 5): Horizontal load: 500 × 1.5 = 750 kN factored per 1.5 m length. Wall thickness: 230 mm RCC, reinforced with vertical 16 mm bars @ 150 c/c extending into deck via anchor bars.
1. Under-sizing carriageway for expected traffic. Rural state highways often specify 5.5-6.5 m carriageway but actual truck dimensions require 7.5 m for safe two-way traffic. IRC 5 sets minimums; size up when expected traffic includes heavy vehicles.
2. Missing the freeboard on waterway bridges. The 50-year flood level from an old hydrology study may have been exceeded by recent floods (Uttarakhand 2013, Kerala 2018, etc.). Verify with a current hydrology assessment, add 1.0 m minimum freeboard for non-navigable streams.
3. Forgetting the approach slab transition. IRC 5 specifies approach slabs to transition between rigid bridge deck and flexible approach pavement. Differential settlement without approach slab creates the familiar 'bump at bridge' — dangerous and expensive to fix post-construction.
4. Inadequate parapet anchorage. The parapet's horizontal load (500 kN per 1.5 m) is not trivial. Reinforcement detailing must properly anchor into the deck slab. Under-designed parapets have failed in India during heavy-truck impacts.
5. Missing night-visibility provisions. IRC 5 requires lighting on urban bridges and reflective markings on rural ones. Night-time bridge accidents are disproportionately high in India — compliance with marking and signage specs is cheap insurance.
IRC 5:2015 is the current edition, a modest update over 2007. Amendment No. 1 (2018) clarified urban expressway standards. Amendment No. 2 (2022) added explicit provisions for cycle tracks and pedestrian overpasses.
Adoption reality: - NHAI projects: strictly follow IRC 5 for all NH bridges, with MoRTH supplementary specs for material and workmanship - State PWDs: vary in compliance — Maharashtra and Karnataka PWDs reference IRC 5 strictly; smaller state PWDs sometimes use older IRC 5:2002 templates - Private/industrial bridges: often exceed IRC 5 minimums for safety; client preference
Unresolved gaps: IRC 5 doesn't explicitly cover modern features like smart-toll gantries, bridge health monitoring instrumentation, pedestrian/cyclist separated paths for tourist areas, and emergency lay-bys. For these, supplement with MoRTH specs or international references (AASHTO, Eurocode).
For design reviews on any road bridge, always start by confirming: carriageway width vs IRC 5 minimum, vertical clearance vs flood level or navigable height, parapet design per Clause 215 of IRC 6, expansion joint spacing per IRC 5 Clause 113. These four items catch 80% of IRC 5 compliance issues.
| Parameter | IS Value | International | Source |
|---|---|---|---|
| Lane width | 3.75m | 3.6m (12 ft) | AASHTO |