IRC 9:1972 is the Indian Standard (IRC) for traffic census on non-urban roads. IRC 9:1972 is the foundational code for traffic census methodology on non-urban Indian roads — national highways, state highways, major district roads, and other district roads. Traffic data is the ground truth for road design, capacity analysis, pavement thickness selection, and economic evaluation. IRC 9 specifies minimum 7 consecutive days of counting for annual estimation, decennial comprehensive census, vehicle classification (2W, 3W, Car, LCV, Truck, Bus, MAV, etc.), PCU conversion factors, seasonal variation factors, directional splits, and growth projections. Amendment No. 1 (2015) added automatic electronic counter specifications (video, pneumatic tube, inductive loop); Amendment No. 2 (2022) added GPS-based O-D data collection methods and ITS integration. Traffic census is now partially automated — National Transport Planning and Research Centre (NATPAC) operates continuous count stations on major NH for real-time data. State PWDs are upgrading to electronic counting. However, data quality issues remain: manual counts have ±10-15% error, and long-term archives are inconsistent.
Specifies methodology, sample size, duration, classification, and reporting requirements for traffic census on non-urban roads (NH, SH, MDR, ODR) — the fundamental data input for road design, capacity analysis, pavement design, and economic evaluation.
- Status
- Current
- Usage level
- Essential
- Domain
- Transportation — Traffic Engineering / Data
- Type
- Recommended Practice
- Amendments
- Amendment No. 1 (2015) — automatic electronic counter specifications; Amendment No. 2 (2022) — GPS O-D data collection, ITS integration
Also on InfraLens for IRC 9
Practical Notes
! 7-day count should include at least one weekend — weekday vs weekend traffic often differs 30-50% on arterials. Weekend-only counts are typically under-representative.
! Seasonal variation factors are corridor-specific. Kolkata-Siliguri NH34 has huge Durga Puja and Poila Baisakh peaks; Goa coastal highway has December tourism peak — apply corridor-specific factors.
! Manual classified counts are accurate but labour-intensive (~4 observers × 24 hours × 7 days = 672 person-hours per station). Automatic counters 80-90% cheaper per station but need calibration.
! Pneumatic tube counters fail on potholed pavements (tube gets damaged). Use inductive loop or video counters on worn pavements.
! Video-based counters with AI classification now mainstream — NHAI has deployed on DMIC expressway, Samruddhi Mahamarg. 95%+ classification accuracy.
! Axle-load surveys (separate from traffic census) equally important for pavement design. Portable weighing station collects axle weights; combined with volume gives ESAL (Equivalent Single Axle Load).
! Growth rate projection: 5-8% annual is standard for NH. Recent data suggests 3-5% for mature NH corridors and 10-15% for new expressways. Verify with 3-year historical growth.
! PCU conversion: IRC 64 gives standard factors; corridor-specific variations possible for truck-heavy vs passenger-heavy routes. Re-calibrate PCU using local observations when practical.
! Directional split (e.g., 70:30) matters for capacity analysis — peak-direction flow is critical constraint. Non-urban highways typically 55:45 to 60:40 directional, higher during commute.
! Peak Hour Factor (PHF) at 0.08-0.12 means peak hour traffic is 8-12% of daily. For urban/interstate PHF is higher (0.10-0.13) due to commute pattern.
! Data archiving: corridor-level electronic database essential. Many state PWDs lost historic census data — rendering trend analysis impossible.
! DPR stage: traffic forecast 30-year horizon is basis for investment decision. 30% error in growth projection (not uncommon) translates to wrong road capacity decisions.
! Bus vs truck ratios matter: bus-heavy corridors need different design (wider passing lanes, bus bays) vs truck-heavy (stronger pavement, wider shoulders).
! Cross-border traffic (e.g., Nepal, Bangladesh borders): separate counting for international traffic; often under-reported due to informal border crossings.
! Origin-Destination (O-D) surveys: separate from volume census; uses roadside interview or GPS-based tracking; provides travel pattern matrix — essential for network planning.
! Speed-and-delay surveys: using floating car technique, drive-along a corridor timing speed drops. Identifies bottlenecks — essential for upgrade prioritization.
! Modern trend: smartphone-based O-D data (via Google, Uber, etc.) increasingly replaces traditional interview surveys. Cost-effective but needs data access agreements.
! Truck driver compliance: many trucks exceed axle-load limits. Census must capture this — combine with weighbridge data where available.
! For PPP BOT projects, traffic projections are basis for toll revenue forecast. Overestimation (common in concessionaire bids) leads to project failure — conservative traffic projections recommended.
! Covid impact on traffic census (2020-2021): significant disruption. 2022+ data more reliable for post-Covid projection. Historic 2017-2019 data useful baseline.