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    PEDMOD
    LEDGA
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(Pavement Evaluation Design Model) was developed originally for the Commonwealth of Virginia and has been used by the United Nations, Ministry of Transportation and Communications in Taiwan, and the Washington State County Roads Administration Board to support pavement management decisions for road networks. Due to its modular construction, the software can be tailored or modified to meet the particular requirements of user agencies.

The PEDMOD computer program was developed to provide a user-friendly, integrated software system for the structural evaluation and design of highway and road pavements. PEDMOD is based on layered elastic theory, which uses the elastic modulus (E) to characterize the strength and engineering properties of pavement materials and subgrade soils.

The program was developed to utilize nondestructive test (NDT) data from commercially available NDT equipment (e.g., Road Rater, Dynaflect, Falling Weight Deflectometer (FWD)) to:

• determine the strength of existing pavement layers and subgrade
• evaluate the expected performance of a variety of pavement systems
• design alternatives for pavement rehabilitation
• determine the life cycle cost of rehabilitation alternatives

To provide the user with the flexibility to update the analytical software as technology changes, a modular concept was employed in the software development. The core module consists of the layered elastic codes, which interact with user inputs and criteria modules to compute: strength (elastic modulus of in-situ pavement layers and subgrade); effective AASHTO structural number; 18-kip equivalent single axle load (ESAL) repetitions; expected pavement structural life; allowable axle and wheel loads; design alternatives for rehabilitation and strengthening; life cycle costs of each alternative.

PEDMOD is structured as a series of interacting components to aid in the computational process. The major components include:

NDT - This component processes the NDT data to be usable in an analytical evaluation and design sequence by allowing the user to automatically import the NDT field data into a spreadsheet file and reduce the field data to determine layer and subgrade strength (i.e., elastic modulus).

Evaluation - This component is used to evaluate the expected structural performance of an existing pavement system under forecasted loading and has the following capabilities:

-	18-kip ESAL Repetitions	-	to convert mixed traffic to the 18-kip equivalent single axle load (ESAL) standard.
-	Effective Structural Number	-	to compute the AASHTO Structural Number of the existing pavement.
-	Expected Life Calculation	-	to estimate the time to the next rehabilitation project based on projected structural performance.
-	Load Limitations Calculation	-	to determine the maximum theoretical axle load an existing pavement can withstand (for a particular traffic level) such that a structural overlay will not be required.

Design - The Design Component allows computation of both asphalt and concrete overlay thicknesses on existing asphalt or concrete pavements, as well as design of new (or reconstructed) asphalt or concrete pavement. Each pavement type incorporates either aggregate or stabilized base layers.

Life Cycle Cost - This component allows the user to compute the total life cost (i.e., construction, periodic maintenance, etc.) of each design alternative.

Report - The program's report feature enables the user to print out a concise, one page summary of program output.

The PEDMOD program will provide the user with an objective reference for analysis of pavement needs, determining objective priorities of needs and repairs, selecting cost-effective rehabilitation options and strategies, determining the cost and timing of rehabilitation and maintenance, developing budget estimates and programming maintenance and construction, and formulating fiscal policy and allocating funds.