Estimation of Average Annual Daily Traffic (AADT)

A reliable estimate of travel demand has always been one of the main concerns of transportation agencies. Annual Average Daily Traffic (AADT) is a factor used in planning, design, and management of roads and facilities. The Federal Highway Administration’s (FHWA) current factoring method is widely used by highway agencies to estimate AADTs for a wide range of roads, which are not possible to be covered by permanent counters.

In this method, roads in the same functional class are assumed to have similar traffic patterns, and factors derived from the class can be used to account for seasonal variations of roads within the same class. It has been shown that since road functional class does not represent the seasonal traffic variation on a road, using this method may result in large errors.

This invention is a computer-implemented method for estimating AADT using all historical short-term traffic counts (STTCs) collected to date from a given road segment to create its seasonal traffic pattern. The following two pattern matching techniques are employed to match the seasonal pattern from the STTC site with that of a given permanent traffic counter (PTC) or PTC group. The Minimum Squared Error (MSE) method and the Coefficient of Variations (COV Ratio) method are used to calculate the probability of assigning the road segment under investigation to different PTC or PTC groups.

After a new STTC is available, the seasonal pattern developed will be extended based on this new count and the probabilities of assigning that segment of a road to different factor groups will be updated using a Bayesian approach. Then the PTC or PTC group with the highest probability will be selected; and factors from that PTC or PTC group will be applied to most recent STTC to estimate AADT. Test results show an error percentage of around 10% with this new method, compared to 60% in current methods.

This invention can be used in any transportation agency around the world to estimate AADTs from STTCs. Every province in Canada and state in the United States can use this method to increase the accuracy of their AADT estimation without any additional cost.


The advantages of the new method for estimating AADT using historical STTCs are:

  • Improved accuracy of AADT estimation from STCC
  • Reduced data collection cost
    • Pattern constructed using available historical counts
  • Easy to implement
    • No changes required to existing traffic monitoring programs

Knowing a better estimate of the AADT can facilitate traffic engineering applications and reduce the overall cost by providing the actual required capacity to a highway project without being over-designed (waste of capacity) or under-designed (dissatisfactory of the project).

Stage of Development

The method is developed and has been tested successfully in the field. The software component is developed, but is still undergoing testing for modifications.

Intellectual Property

US & Canadian Patent pending. This technology is available for licensing.

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Office of Research Services, Industry-Government Services 
University of New Brunswick 
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