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Axle Load Surveys: Importance, Methodology, and Best Practices

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Axle load surveys, play a crucial role in determining the pavement actual loads and this will impact a new road design and maintenance in future. These surveys provide essential data for cost-effective pavement design and for the preservation of existing roads. However, axle load surveys can be costly, requiring careful planning and execution to ensure accuracy and efficiency.

Axle load surveys help in the accurate calculation of Equivalent Axle Load Factors (EALF) and Truck Factors (TF). These parameters vary based on axle configuration and axle loads. They are used, along with other factors, to determine the Equivalent Single Axle Load (ESAL) which is a representative value that quantifies traffic loads on pavement, forming the basis for pavement design.



Vehicle Classification in Axle Load Surveys

Different types of vehicles contribute differently to pavement deterioration. It is important to categorize vehicles properly to ensure that the survey results are relevant and reliable.

  1. Light Vehicles

    • Vehicles with a gross weight of less than 5.0 tonnes fall into this category.
    • They cause minimal structural damage to pavements.
    • As a result, they are not included in axle load surveys and do not need to be weighed.

  2. Heavy Vehicles

    • Includes buses with seating capacities greater than 40 passengers and heavy-duty trucks.
    • These vehicles carry large axle loads, which significantly impact pavement conditions.
    • They must always be included in axle load surveys.

Survey Considerations

1. Traffic Direction Analysis

  • Traffic loads in the two directions of a road are rarely identical.
  • There is usually a significant difference in axle loading between directions.
  • Therefore, surveys must separately assess each direction to obtain accurate results.

2. Inclusion of Empty Vehicles

  • Axle load surveys should include both fully loaded and empty vehicles.
  • This ensures a comprehensive dataset, representing all loading conditions.

3. Accuracy in Weighing

To obtain precise measurements, several key considerations must be followed:

  • Vehicles should be weighed on a level surface to prevent inaccuracies.
  • All wheels should rest on an equally leveled surface.
  • If one set of wheels is raised above the others, the measured weight will be lower than the actual weight.
  • Conversely, if the weighed axle is lower than the others, the recorded weight will be higher than the actual weight.

4. Survey Duration

  • Axle load surveys should be conducted for seven consecutive days, 24 hours per day.
  • This duration provides a representative sample of traffic loading throughout the week.
  • Surveys lasting less than seven days are not recommended due to potential data inconsistencies.
  • If conducted at a border gate station, survey hours should align with the station's operating hours.

Axle Load Weighing Equipment

Various equipment types can be used to measure axle loads:

  1. Permanent and Portable Weigh Pads

    • These are used to measure axle weights at stationary locations.

  2. Weigh-in-Motion (WIM) Systems

    • This advanced system measures vehicle weight while the vehicle is in motion at low speeds.
    • It allows for efficient data collection without disrupting traffic flow.

Axle load surveys are essential for designing durable pavements and ensuring the durability of road infrastructure. By carefully planning the survey, considering different vehicle types, and using accurate weighing techniques, traffic engineers can obtain reliable data to support effective road maintenance and design.

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