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Technical Advisory

Types of Specifying

The following guidance has been prepared to help division office personnel recognize and understand the different types of specifications and provisions that a State DOT may prepare and submit for FHWA approval. These specification types may include:

A description of each of these specification types is provided below, along with a discussion of their relative advantages and disadvantages, the project conditions under which they can be best implemented, and the general information that they should convey.

  1. Method specifications

    1. Description. Method specifications (also called material and method specifications or prescriptive specifications) explicitly identify the materials and work methods or procedures a contractor should use to complete the work included in the contract. Method specifications typically operate on the principle that if the specified materials and methods worked in the past, then the end product is likely to perform well in service so long as the contractor strictly adheres to the prescribed requirements.

    2. Advantages of method specifying

      1. The State DOT can exert greater control over the work.

      2. The materials and construction steps included in method specifications are typically based on methods that historically provided satisfactory results. Method specifications thereby eliminate risk associated with newer, less proven methods and risk associated with varying contractor performance.

    3. Disadvantages of method specifying

      1. Traditional method specifications specify the materials and means and methods a contractor must use to construct a portion of the work. The contractor therefore has little opportunity to deviate from the specifications, and, provided that the specifications are met, is not responsible for performance deficiencies of the end product.

      2. Method specifications typically base acceptance on the "reasonable conformance" or "substantial compliance" of the work with the specification requirements, as established by the State DOT's inspection of the work. If test results are used as a component of the acceptance determination, usually only individual or representative field samples are taken. These individual results may fail to recognize the inherent variability in the material itself, potentially leading to disputes between the contractor and DOT over acceptance decisions.

      3. Contractor payment is not tied to the performance or quality of the work. Because method specifications do not establish a range of quality levels, they generally do not include procedures for price adjustments. The contractor therefore typically receives 100 percent payment for the work completed when it complies with the requirements of the specification.

      4. The prescribed procedures may prevent or discourage the contractor from using the most economical or innovative procedures and equipment to perform the work.

      5. In order to ensure that the desired product is achieved, the owner must dedicate significant resources to ensure that the correct "method" was used.

    4. Appropriate conditions for use

      1. End product performance is not easily defined.

      2. End product performance cannot be easily or economically measured and verified.

      3. Limited methods exist that would satisfy the DOT's minimum requirements.

      4. The State DOT must retain performance risk because of permit requirements, maintenance considerations, need to tie into existing or adjacent construction, and similar issues.

      5. Removing and replacing defective work would be impractical.

    5. Elements of a method specification.Understanding the main elements of a method specification will help reviewers identify missing information that needs to be added to the specification and any nonessential information that can be eliminated. The following discussion assumes the specifications generally follow an AASHTO format. However, it is important to know and understand the format and organization used by a particular State DOT when reviewing a specification to ensure that (1) all the necessary information is included and (2) that this information is included in the correct location.

      1. Description of the work. Technical specifications typically begin with a subpart entitled Description of the Work, Scope of Work, or similar. The intent of this subpart is to provide a concise statement of the work required.

        1. To clarify the work included, this subpart may also be used to describe the relationship of the work included under this specification to other work items, referring to related plans or specifications as necessary.

        2. The Description of Work should not include methods of construction, construction details, and procedures for measurement and payment, as this information is better suited to other subparts.

        3. Similarly, phrases such as "...in accordance with these specifications and in reasonably close conformity with the lines, grades, thickness, and typical cross-section shown on the plans, or as directed by the Engineer..." are generally not necessary to repeat in the Description of Work. Such information is already included in the General Provisions (Division 100), eliminating the need to repeat it elsewhere in the technical specifications.

        4. Some State DOTs also use this subpart to define terminology specific to the work required under the specification or to specify special submittal requirements.

      2. Material (and equipment) requirements. This subpart should identify and describe the materials the contractor is to use to complete the work.

        1. The Materials subpart often cross-references more detailed State DOT material specifications located in another division or book, or nationally recognized reference standards. The specifications should address salient material properties, while avoiding unnecessary restrictions that may be difficult or impossible for the contractor to meet.

        2. The method(s) of sampling and testing and the applicable acceptance procedures are typically included with the construction requirements, not the materials requirements.

        3. A few agencies also use this section to describe equipment
          requirements (e.g., asphalt plants).

        4. When reviewing Materials subparts, consider the following:

          1. Is the specified material proprietary?

          2. Is the State DOT providing any material or designating
            material sources?

          3. Are cross-references to other material requirements or
            national reference standards appropriate?

          4. Does a cross-referenced specification allow the contractor to select materials from multiple options? If so, is it necessary to stipulate a specific option?

      3. Construction requirements. This subpart should describe how the contractor is to accomplish the required work and how the State DOT will determine the acceptability of that work. The recommended Construction subpart should:

        1. Provide sufficient specification requirements to ensure quality of workmanship and satisfactory completion of the work. Consider the extent to which prescriptive requirements regarding construction operations, special equipment, and other controls are necessary.

        2. Complement, not duplicate, the information on the plans.

        3. Describe the necessary submittal and shop drawing requirements.

        4. Include a clear description of restrictions applicable to the completion of the work. These restrictions may be in the form of administrative requirements, intermediate steps of approval or verification, or the methods of transfer of information between the State DOT and the contractor.

        5. Specify allowable tolerances and applied penalties, if any, for exceeding specified tolerances.

        6. Specify the type and frequency of testing required during construction.

        7. Identify the minimum quality control activities to be performed by the contractor.

        8. Identify the quality assurance activities (testing and inspection) that the State DOT will perform to determine the acceptability of the work.

      4. Measurement and payment. The specification should identify how items of work will be measured and paid for. The recommended measurement and payment subpart(s) should:

        1. Specify how quantities will be determined (e.g., in place, loose vs. compacted, etc.).

        2. Specify any adjustments to the measured quantity (e.g., waste, spillage, overlaps, etc.).

        3. Define all pay items needed to complete the work, and the units of measurement for each item.

        4. Ensure that the bid item includes all labor, materials, and equipment related to the work, or otherwise identifies work that is to be paid for under other bid items or that is incidental to the payment.

        5. Identify all necessary preceding and succeeding events that could
          have a bearing on the time and place of measurement.

        6. Reflect the responsibility and completion definitions included in the work description.

        7. Identify the payment range (from increase of 100 percent or higher to reduction to the point of rejection/removal) for the applicable material to promote better quality. Reduction in pay factor should be based on sound engineering judgment and remaining material properties that account for subsequent maintenance concerns due to a reduced service life.

  2. Performance specifications

    1. Description. Performance specifications describe the required work in terms of operational characteristics or ultimate use. The performance characteristics are designed to predict or monitor performance over time. Unlike method specifications, performance specifications tend not to include instructions that dictate or suggest methods, material definitions, material processing, time and temperature controls, constituent properties, construction equipment descriptions, and similar prescriptive elements.

    2. Subsets of performance specifications. The term performance specification can be used as an umbrella term to capture several types of specifications, including end-result specifications, QA specifications, performance-related specifications, performance-based specifications, and performance warranty provisions.

      The AASHTO Highway Subcommittee on Construction, Quality Construction Task Force, has prepared a report entitled Major Types of Transportation Construction Specifications, A Guideline to Understanding their Evolution and Application, which describes these various specification types and how they should be developed and implemented.

      1. End-result specifications assign to the contractor complete responsibility and flexibility in selecting the procedures and equipment for supplying a product or an item of construction. The State DOT's responsibility is to either accept or reject the final in-place product or to apply a pay adjustment commensurate with the degree of compliance with the specifications.

        1. End-result specifications look to measure or test the in-place end product and, at the same time, reduce the amount of prescriptive elements of the specification.

        2. For example, one could specify a chip seal based on a measured chip density and retainage, and eliminate requirements related to the spreader equipment and flow details. Another common application of end-result requirements occurs in specifications that measure compaction but do not dictate roller types or roller passes.

        3. Because end-result specifications offer the contractor flexibility in exercising options for new materials, techniques, and procedures to improve the quality or economy, or both, of the end product, they are often incorporated into design-build contracts as performance specifications.

      2. Quality assurance (QA) specifications require contractor quality control and State DOT acceptance activities throughout the production and placement of a product. Final acceptance of the product is usually based on a statistical sampling of the measured quality level for key quality characteristics.

        1. The critical aspect of developing QA specifications is identifying the material attributes that are essential to good performance and the associated limits within which the material or work can be produced to suggest good performance over the design life of the product. For example, for asphalt pavements, key quality characteristics might include asphalt content, density of the compacted pavement, and pavement smoothness. For concrete pavement, quality characteristics could include compressive strength, air content, and smoothness.

        2. Note that many agencies have already implemented QA specifications as part of their standard specifications for asphalt and concrete pavement. Refer to FHWA-RD-02-095, Optimal Procedures for Quality Assurance Specifications, for more detailed information regarding the development of acceptance plans and QA specifications.

      3. Performance-related specifications (PRS) are essentially improved QA specifications that describe the desired levels of key materials and construction quality characteristics that have been found to correlate with fundamental engineering properties that predict performance. Price adjustments are based on life-cycle cost relationships.

        1. PRS identify and quantify those particular technical factors that influence product performance. They may use empirical data, engineering judgment, mechanistic modeling, and life-cycle costing as the basis for determining the potential for performance.

        2. Like QA specifications, PRS only specify characteristics (for example, air voids in asphalt and compressive strength of concrete) that lend themselves to acceptance testing at the time of construction. They do not specify the desired long-term product performance.

        3. "True" PRS use mathematical models to predict performance based on the measured quality characteristics (e.g., asphalt content, air voids) and design variables (e.g., traffic loading, climate). The models provide the rationale for acceptance and pay adjustments based on life-cycle costs.

        4. Implementation of PRS is dependent on the development and validation of such models. To date, PRS have only been piloted on concrete pavements, though research is also being performed on asphalt.

      4. Performance-based specifications (PBS) are QA specifications that describe the desired levels of fundamental engineering properties (e.g., resilient modulus, creep properties, and fatigue properties) that are predictors of performance and appear in primary prediction relationships (i.e., models that can be used to predict pavement stress, distress, or performance from combinations of predictors that represent traffic, environmental, roadbed, and structural conditions).

        1. Performance-based specifications differ from PRS in that they specify the desired levels of fundamental engineering properties, rather than key quality characteristics.

        2. Complete PBS have not yet been applied in highway construction, primarily because most fundamental engineering properties are only now becoming amenable to timely acceptance testing.

      5. Performance warranty provisions incorporate performance indicators and thresholds to measure performance over a prescribed warranty period.

        1. Warranty performance indicators are measurable distresses, properties, or characteristics of the warranted component that can be linked to the end-product performance of the warranted component. For example, performance indicators for asphalt pavement may include rutting and cracking. Performance thresholds can be expressed in terms of physical dimensions per segment length or converted to a point system. Thresholds are the allowable limits not to be exceeded over the performance period.

        2. Warranties typically do not include all the factors that contribute to performance. For example, warranty provisions for pavements typically exclude subbase, drainage, and embankment features or other factors related to pavement design or construction methods that may affect performance.

        3. Although the scope of warranted work and performance indicators may not capture all of the factors contributing to performance, they provide a tool to assign more responsibility for performance to the private sector and ensure that the products of construction will meet targeted performance thresholds for part of the life-cycle of that product or component.

    3. Elements of a performance specification. A well-drafted performance specification generally contains the following elements.

      1. Identification of owner's needs or goals

        1. In the ideal application of performance specifying, the owner defines its needs at the highest possible level. For example, for pavements such goals could be safety, comfort, accessibility, and capacity. Lower level requirements, such as material or manufacturing properties (e.g., aggregate gradation), should be included only when necessary and where definitions for desired performance cannot otherwise be expressed in clear and unambiguous terms.

        2. In practical application, however, specifying at the user needs level can be difficult for highway agencies. For example, most road users and communities simply want a road that is safe and accessible and that meets traffic demands. However, the State DOTs must also consider the need to tie into existing systems, comply with permit conditions, meet right-of-way constraints, and suit existing maintenance operations. Such considerations, among others, often lead the State DOTs to develop specifications that contain a hybrid of performance and prescriptive elements.

      2. Performance parameters

        1. Performance parameters are functional requirements that ideally can be measured or tested to ensure that the owner's project goals are satisfied. For example, possible performance parameters for an asphalt pavement could include smoothness, in-place density, and asphalt content. In warranty contracting, performance parameters are typically referred to as "performance indicators."

        2. It can be a challenge to identify all of the parameters necessary to produce an acceptable product, without including nonessential requirements that will hinder contractor innovation, require additional testing resources, or force the State DOT to continue to retain the bulk of the performance risk.

        3. When identifying performance parameters, consider the following:

          1. What physical properties are considered to be critical to performance?

          2. How can these properties be tested and measured?

          3. To what degree does each physical property influence performance?

          4. What price adjustment, if any, should be applied to these properties?

          5. Are all factors associated with the parameter within the contractor's control? (For example, if the contractor is not 31 responsible for the subgrade conditions, it may be reluctant to accept responsibility for certain parameters, such as structural deflection.)

          6. Does the parameter reflect end-of-construction quality only? Is a warranty provision necessary to ensure that the required performance is met over time?

      3. Measurement or testing technique. The specification should identify a measurement strategy for each performance parameter. For example, pavement smoothness could be measured using a high speed profilograph.

        1. The most desirable performance parameters are measurable and testable. When identifying possible measurement techniques, consider the following:

          1. Can measurement and testing be done in a manner that has minimal impact on traffic and lane closure?

          2. Can the data be processed in a timely manner?

          3. In comparison to other testing techniques (or use of method specifications), is the measurement and testing economical, considering the dollars per test multiplied by the number of tests required based on the uniformity of the material?

          4. Do the measurement techniques require a high skill level from technicians? Are special certifications necessary?

          5. Is specialized equipment necessary? If so, should the contractor provide this equipment or should the State DOT?

          6. Are standardized tests available? Do the tests provide repeatable results?

          7. Are "referee" tests available in the event that the State DOT or contractor disputes the results of the initial testing?

        2. Ideally, the performance parameters should be quantifiable. However, certain requirements (e.g., those involving aesthetics) may still involve the engineer's judgment. For such subjective items, the engineer and contractor should mutually develop and agree to an acceptance standard for that parameter. For example, a visual standard can be established by inspecting a representative sample early in the project.

        3. In establishing and defining the overall measurement strategy, the specification should identify how often the measurements should be taken (e.g., continuously; start and end of project only; on some periodic basis; etc.), who should be collecting and witnessing the 32 taking of samples, and who should be taking the measurements (e.g., contractor, DOT inspector, independent inspection firm).

      4. Performance value or threshold

        1. For each performance parameter, the specification should set a performance value, expressed in terms of ranges (minimum/maximum), thresholds, or a rating system. For example, a performance value associated with pavement smoothness could be expressed as a maximum IRI in inches/mile.

        2. When setting performance values, consider the following:

          1. If the values for parameters are set based on the use of predictive models, has the model been tested and confirmed to produce reliable results? Does the model need to be calibrated to reflect regional conditions?

          2. Do the values represent end-of-construction conditions, or some point during a warranty or operation period?

          3. If the values are not met, should a pay adjustment be applied? Would remedial action be necessary?

      5. Verification tests or inspection

        1. When using performance specifications, the contract should require the contractor to develop, submit, and implement a plan to control the quality of materials and construction. The State DOT may specify minimum requirements to ensure a base level of quality control is performed.

        2. Even though the contractor may assume more responsibility for inspection and testing under a performance specification, this in no way relieves the State DOT of its responsibility to perform its own oversight and independent verification to ensure that the product meets or exceeds the stated objective or standard.

        3. The type and extent of verification that the State DOT will perform as part of its acceptance plan should be clearly outlined in the specification. This information will help the contractor coordinate the testing and inspection schedule with the progress of the work.

      6. Price adjustment

        1. Unlike method specifications, performance specifications allow the parties to acknowledge a range of acceptable work quality through the use of price adjustments that reflect the value of the work received.

        2. Ideally, price adjustments should be based on a life-cycle cost analysis.

          1. A negative pay adjustment or disincentive would cover the cost of future maintenance and rehabilitation due to the construction not meeting the designed level of quality.

          2. A positive adjustment would reflect the savings in maintenance and rehabilitation due to the higher level of initial quality. The FHWA has traditionally endorsed the use of incentive payments of up to 5 percent of the unit bid price for improved quality.

          3. It is also important to ensure that specifying a positive pay factor for one property will not detract from achieving sufficient quality on another. (For example, for a continuously reinforced concrete pavement, a higher-thandesigned thickness and strength could cause wider crack spacing or excessive stress in the reinforcing steel.)

    4. Advantages of performance specifying

      1. The contractor assumes more performance risk.

      2. Contractors have the flexibility to select materials, techniques, and procedures to improve the quality or economy, or both, of the end product.

      3. Performance specifications increase the potential for contractor innovation.

    5. Appropriate conditions for use

      1. End product performance is measurable.

      2. Testing is rapid, available, and economical.

      3. Contractors are willing to assume performance risk because they are in a
        position to control the risk or are attracted to the possibility of increased

  3. National reference standards

    1. Description. National reference standards refer to specifications prepared by recognized trade associations, professional societies, standards-writing organizations, or agencies that provide national standards of performance or measurement. These specifications have been proven over time to provide the desired quality. Reference standards may include prescriptive requirements, but more typically include end-result requirements, criteria, and tests to meet a desired standard of performance. They can be incorporated into a method or performance specification.

    2. Examples. National reference standards used in transportation specifications may include:

      1. AASHTO Standards for Materials and Methods of Sampling and Testing,

      2. American Society of Testing and Materials (ASTM) standards for testing, materials and workmanship;

      3. American National Standards Institute (ANSI) product standards;

      4. Design standards from American Concrete Institute (ACI) and American Institute of Steel Construction (AISC);

      5. Federal Specifications and Standards (General Services Administration); and

      6. Military Specifications and Standards (Department of Defense).

    3. Application. To properly incorporate reference standards into a specification, they should be referred to by number, title, or other designation. This will make the standard part of the specification, just as if it were included in its entirety. Reiterating any part of the standard in the specification is therefore an unnecessary practice that should be avoided to prevent misinterpretation by contractors and inspectors (for example, users may think that they are held to only the quoted portions).

      1. Verify that the reference standard does not duplicate or contradict other contract requirements. This requires a thorough review and understanding of the reference standard, including all other standards that may be referenced within the primary standard. If necessary, the specification can define exceptions to the reference. The order-ofprecedence clause should also state that project-specific requirements govern over the requirements of reference standards.

      2. Reference standards often define quality in terms of minimum requirements. Ensure that the stated requirements match the designer's intent, and are not so liberal that practically anything will be considered acceptable. Similarly, the reference standard should not include requirements that are more restrictive than necessary, leading to higher costs or to a proprietary specification. The specification should explicitly define all exceptions taken to the reference standard.

      3. It is important to also recognize that the specification of an industry standard does not in and of itself ensure a competitive bid process. A reference standard may so narrowly define a product that only a single provider can meet the requirements, leading to a proprietary specification.

  4. Proprietary products and specifications

    1. Description

      1. Proprietary specifications identify the desired products or processes by manufacturer's name, brand name, model number, or other unique characteristic. Even if a manufacturer is not explicitly stated, a specification can still be considered proprietary if only one manufacturer can meet the specified requirements.

      2. Designers often specify proprietary products to produce what they perceive to be a "tight" specification that allows for close control of product selection and a higher level of design based on more precise information obtained from manufacturer's data. However, this practice introduces the potential disadvantages of unnecessarily eliminating or narrowing competition or requiring products with which the contractor has perhaps had little or poor experience (e.g., slow delivery) - situations that may lead to higher bid prices or charges of favoritism.

    2. Current policy. 23 CFR 635.411(a) allows use of a patented or proprietary material, specification, or process under the following circumstances:

      1. The item is obtained through competitive bidding with a reasonable number (as determined by the division office) of equally suitable proprietary and nonproprietary products.

      2. The State DOT certifies that:

        1. the patented or proprietary product is necessary to ensure compatibility with existing facilities or systems (e.g., the proprietary product is necessary to match the visual appearance of existing facilities; the product is interchangeable with products in the DOT's existing maintenance inventory; or the product is necessary to ensure functionality, such as the need for a certain model of controller for an existing traffic signal system); or

        2. no equally suitable alternative exists.

      3. The proprietary product is to be used for research or for a distinctive type of construction on relatively short sections of road for experimental purposes. Note that if this option is applicable, the State DOT must submit a written work plan to the division office for review and approval that describes the experimental feature and the objectives of incorporating it into a project. Refer to the FHWA Web page on experimental features for more information.

    3. State DOT certifications. A State DOT certification as to the necessity of a proprietary product because "no suitable alternative exists," should contain the following information:

      1. A description of how the proprietary product will benefit the public;

      2. An evaluation of the available products, and why these products cannot meet the DOT's needs; and

      3. An estimate of additional costs associated with specifying the proprietary product.

    4. Public interest finding (PIF)

      1. The Division Administrator may approve a single source if it can be determined that doing so would be in the public interest. The justification for the PIF should consist of an engineering and economic analysis that addresses the following questions:

        1. Are there other products on the market that meet the specifications?

        2. Are these products of satisfactory quality?

        3. Are the anticipated costs for the products approximately the same?

      2. A PIF is not necessary when a reasonable number (as determined by the division office) of nonproprietary or proprietary products from multiple manufacturers are listed as possible sources. The specific characteristics of the proprietary product should also be identified in the specification (e.g., reflective properties of pavement marking tape or width and length of crashworthy end treatments). This information would help personnel determine if a substitute product is indeed "or equal".

      3. When reviewing a PIF for approval, division office personnel should research the information contained in the PIF Database maintained on the research center's Stewardship Portal. The database is a valuable resource, storing hundreds of noted PIFs, which can serve as examples for the division offices to promote efficiency and uniformity in the development and approval of PIFs.

    5. References. For more information related to proprietary products, consult the following references:

      1. Contract Administration, Core Curriculum, Participant's Manual and Reference Guide 2006, Chapter IIC.5.b., Patented/Proprietary Products

      2. FHWA Construction Guide, Patented and Proprietary Products

      3. Guidance on Patented and Proprietary Product Approvals - FHWA Memo, January 11, 2006

      4. Product Selection - FHWA Memo, November 25, 1987

      5. Questions and Answers Regarding Title 23 CFR 635.411

      6. FHWA Construction Projects Incorporating Experimental Features
Updated: 06/27/2017
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