Traffic Survey

A traffic survey is the systematic measurement of vehicle volumes, types, and movements on a road corridor, used in highway project preparation to design the correct pavement structure, estimate capacity requirements, and project future toll revenues for PPP highway contracts. Accurate traffic data is the foundation of sound highway investment decisions.

What is a Traffic Survey in government procurement?

Traffic surveys for highway planning are procured as consultancy services by NHAI, MoRTH, state PWDs, and highway agencies. The main types of traffic surveys used in Indian highway project preparation include the following.

Traffic Volume Count (TVC) is the basic survey, counting all vehicles passing a defined point on the road, classified by vehicle type (two-wheelers, cars, light commercial vehicles, buses, 2-axle trucks, multi-axle trucks, tractors). It is conducted over 7 consecutive days to capture weekday-weekend variation and is done over 24 hours to capture peak hour patterns. TVC results are expressed in Passenger Car Units (PCU), a unit that converts all vehicle types to a car-equivalent for capacity analysis.

Axle Load Survey measures the weight carried by vehicles using weigh-in-motion equipment at the roadside. This is critical for pavement design, the pavement must withstand the cumulative load of all heavy vehicles over the design life (typically 20-30 years for national highways). A road carrying many overloaded trucks requires a much thicker pavement than one carrying predominantly cars.

Origin-Destination Survey captures where vehicles are coming from and going to, essential for understanding which traffic will use a bypass or expressway, and which will remain on parallel roads. OD surveys use roadside interview methods or, increasingly, GPS-based phone data analytics.

Turning movement counts at major intersections determine the traffic volume through each turning movement, informing signal timing design, slip road design, and grade separation decisions.

Traffic surveys for HAM and BOT-Toll concessions require special rigour because they directly underpin the financial model. The concessionaire's lenders commission their own independent traffic study before approving project finance, this secondary independent study often reveals differences from the DPR traffic study that affect the project's financial projections.

Why it matters for bidders

For consultancy firms bidding traffic survey contracts, the key credentials are: experience of NHAI-level TVC studies, NABL-accredited laboratories for weigh-in-motion calibration, and transport planning modelling capability for traffic projection. Traffic survey contracts are often bundled with the broader DPR consultancy or survey and investigation package.

For highway EPC contractors, traffic survey data from the DPR determines the pavement thickness they must construct, a direct cost driver. Contractors who suspect the DPR's traffic projections are high (leading to an over-designed pavement that is costly to build) can raise this at the pre-bid stage.

For HAM concessionaires, the traffic survey is the single most commercially sensitive technical document. A concession that was bid based on optimistic traffic projections will under-recover annuity sufficiency throughout the 15-year operation period. Concessionaires should critically review the DPR traffic study and, for significant projects, commission an independent peer review before bidding.

Example

NHAI's DPR for a proposed HAM section of NH-48 in Tamil Nadu includes a traffic survey showing Average Daily Traffic (ADT) of 28,000 vehicles, with 22% commercial vehicles. The pavement is designed for 150 million standard axles over 20 years. A potential HAM concessionaire's due diligence team reviews the traffic study. They note the survey was conducted in October, a low-traffic period in this corridor due to festival season disruption. An independent traffic survey commissioned by the concessionaire during January shows ADT of 24,500, 12.5% lower. The concessionaire adjusts its annuity adequacy model and bids a higher Bid Project Cost than it would have based on the DPR traffic data alone, winning the bid margin over the more optimistic competitors who took the DPR data at face value.

Key rules / thresholds

IRC 9 (Code of Practice for Traffic Counts on Non-Urban Roads) and IRC 64 (Recommended Practice for Traffic Studies) govern traffic survey methodology in India. For World Bank-funded highway projects, traffic studies must meet the Bank's transport data quality standards. Axle load surveys for pavement design must follow IRC SP:30 guidelines. Traffic projections typically use 8-10% annual growth rate for the first 5 years, reducing to 5-6% in subsequent periods, based on historical growth and GDP correlation studies, though individual project projections vary.