Rolling Wheel Deflectometer

Network-level Pavement Structural Evaluation

Measuring Deflection at Highway Speeds

Fast - Reliable - No Lane Closures Required

Each year millions of dollars are spent on reconstruction, rehabilitation and maintenance of the Nation’s highways, mostly for pavements. Prioritizing needs and targeting scarce highway funds are critical issues for highway officials. One of the newest tools available for managing asphalt pavements is a device designed to measure pavement deflections while traveling at highway speeds. This device, known as the Rolling Wheel Deflectometer or RWD, was designed to provide deflection information that can be used as a relative measure of the structural capacity and stiffness of asphalt pavements. Data can be collected on 200 to 300 miles per day and can usually be done without additional traffic control vehicles. The data are used to provide a "structural map" of an entire highway network and to target areas for detailed inspection and testing using a Falling Weight Deflectometer, coring, or other static types of testing. With the RWD, an agency can concentrate resources on those areas most needing attention.

The RWD is constructed using a specially designed tractor-trailer to load the pavement and measure deflection responses. The tractor houses the operator, laser controls, and computer equipment for the device. The trailer is 53 feet long and was specially designed to control pitch and roll. The trailer has a single rear axle that is loaded to 18,000 lb (1 ESAL). The equipment includes four high precision laser measuring devices which are mounted 8.5 feet apart with the rearmost laser placed between the rear wheels and just behind the centerline of the rear axle. (See photo)

Extensive demonstration testing has been completed during the past 5 years. Efforts were made to operate the vehicle over various types of roadways to address concerns and evaluate the performance on hills, curves, soil conditions, traffic loadings, and different kinds of asphalt mixes.

Findings from the RWD Demonstration Program

• Correlates with other devices.
• Little sensitivity to speed of collection.
• Useful only for flexible pavements.
• Not affected by curves up to 8%.
• Operates day or night but not in the rain.

Benefits of Using the RWD

• Determine structural health of the whole system.
• Focus expensive testing to high need areas.
• Simplify tracking of roadway performance.
• Limit exposure of personnel to hazardous traffic.

RWD Future Programs

Projects are currently underway to integrate RWD data into Pavement Management System models and demonstrate it's value in supporting the decision making process. The RWD will add a structural component to the other surface condition data used in PMS analysis models. The overall outcome will be a more robust prediction of pavement conditions that can be used to focus rehabilitation work and optimize available funds for maintenance and reconstruction. This demonstration will be designed to work with most of the pavement management software products currently in use in the United States. The Rolling Wheel Deflectometer is currently available for commercial service through a special agreement with our Contractor, Applied Research Associates.

When developing long- and short-term programming and budgeting plans, it is critical that transportation agencies start with clearly defined performance objectives for their assets, including safety. Plans must be data driven and must include performance measures that relate to policy objectives. Engineering and economic analysis and risk assessment are especially important when trade-off decisions are made on how to best address the transportation agency's many needs, as well as support which projects will be funded based upon quality information and analysis. Plans also need "safety champions" who can lead the coalition of stakeholders.

Available Reports

As a result of the demonstration program over the past five years, we have the following reports describing the testing program and findings from each State in the program. Although all of the programs contain some similarities (i.e. comparing the results against FWD devices), many of the highway conditions varied from State to State. In addition, most States had particular considerations they wanted to accomplish with the RWD information and each State provided an opportunity to further test the device itself and its various components.

State Reports

• California
• Connecticut
• Indiana
• Iowa
• Kansas
• Minnesota
• New Hampshire
• New Jersey
• New Mexico
• Ohio-Kentucky-West Virginia
• Oregon
• Texas
• Vermont
• Virginia

Other Testing Programs

• Champaign County, Illinois
• Natchez Trace
• NCAT Test track