Specifications are used (1) to convey information concerning desired products from a buyer to a seller or potential seller, (2) as a basis for competitive bidding for the delivery of products, and (3) to measure compliance to contracts.  Typically, four types of specifications; proprietary product, method, end-result and performance specifications; are generally recognized in the construction industry.

Figure 1: WSDOT Standard Specifications Books 2012 - 2018

This section is largely taken from a series of three articles written for HMAT Magazine and a Washington State DOT research report as listed below:

  • Newcomb, D.E. and Epps, J.A.  (Jan/Feb 2001).  Statistical Specifications for Hot Mix Asphalt: What Do We Need to Know?  HMAT, vol. 6, no. 1.  National Asphalt Pavement Association (NAPA).  Landham, MD.  (first in a series of 3 articles)
  • Newcomb, D.E. and Epps, J.A.  (Mar/April 2001).  Statistical Specifications for Hot Mix Asphalt: What Do We Need to Know?  HMAT, vol. 6, no. 2.  National Asphalt Pavement Association (NAPA).  Landham, MD.  (second in a series of 3 articles)
  • Newcomb, D.E.  (May/June 2001).  Performance Related Specifications Developments.  HMAT, vol. 6, no. 3.  National Asphalt Pavement Association (NAPA).  Landham, MD.  (third in a series of 3 articles)
  • Muench, S.T. and Mahoney, J.P.  (2001).  A Quantification and Evaluation of WSDOT’s Hot Mix Asphalt Concrete Statistical Acceptance Specification.  WA-RD 517.1.  Washington State Department of Transportation, Transportation Center (TRAC).  Seattle, WA. (https://www.wsdot.wa.gov/research/reports/fullreports/517.1.pdf).
  • Willoughby, Kim and Mahoney, J.P. (2007). An Assessment of WSDOT’s Hot-Mix Asphalt Quality Control and Assurance Requirements. WA-RD 517.2. Washington State Department of Transportation, Transportation Center (TRAC). Seattle, WA. (https://www.wsdot.wa.gov/research/reports/fullreports/517.2.pdf).

Proprietary Product Specifications

A proprietary product specification is used when a generic description of a desired product or process cannot be easily formulated.  It usually contains an “or equivalent” clause to allow for some measure of competition in providing the product.  It is generally acknowledged that such a specification severely limits competition, increases cost, provides little latitude for innovation, and puts substantial risk on the owner for product performance.  Most agencies avoid this type of specification whenever possible, however private owners often use them.

Method Specifications

A method specification outlines a specific materials selection and construction operation process to be followed in providing a product.  In the past, many construction specifications were written in this manner.  A contractor would be told what type of material to produce, what equipment to use and in what manner it was to be used in construction.  In its strictest sense, only the final form of the structure can be stipulated (for instance, the thickness of the pavement layers).  This type of specification allows for a greater degree of competition than the proprietary product specification, but as long as the structure is built according to the materials and methods stipulated, the owner bears the responsibility for the performance.

Although widely used, method specifications have several key disadvantages.  First, they tend to stifle contractor innovation because there is virtually no incentive to develop better, more efficient construction methods.  Second, since they are not statistically based and 100 percent compliance is usually not possible, method specifications usually required “substantial compliance,” a purposely vague and undefined term that can lead to disputes.  Finally, spot checks of material quality, which are often used in method specifications, do not reflect overall material quality because they are taken from subjectively determined non-random locations.  Since they are not random, these spot checks have no statistical validity and therefore do not reflect overall material quality.

Despite their flaws, method specifications are still widely used on the local agency level (e.g., counties, small cities, towns, etc.).  In general, this is because they are familiar, straightforward to write and can be implemented with minimal agency involvement.  Local agencies often lack the expertise and resources required to use statistical specifications or warranties.

End-Result Specifications

An end-result specification is one in which the final characteristics of the product are stipulated, and the contractor is given considerable freedom in achieving those characteristics.  In their roughest form, they specify minimum, maximum or a range of values for any given characteristic and base acceptance on conformance to these specifications.  For instance, they may state a minimum layer thickness or a range of in-place air voids.  Since it is impractical to measure every square foot of constructed pavement, end-result specifications use statistical methods to estimate overall material quality based on a limited number of random samples.  Therefore, end result specifications improve on methods specifications in two key areas: (1) they shift the focus away from methods and on to final product quality and (2) they do not rely on the nebulous “substantial compliance” because they clearly define acceptable quality.

Today, most large State and Federal pavement contracts use statistically based end-result specifications that incorporate some elements of method specifications (usually used to guard against early failure of the product).  These end-result specifications are often referred to as a “quality assurance specifications”, “QA/QC specifications” or “QC/QA specifications”.  Essentially, these specifications specify the end results and also specify certain minimum construction method requirements (e.g., temperatures below which paving is not allowed, descriptions of initial test sections, minimum number of rollers, conditions under which the agency may halt paving operations, etc.).

End result specifications assign pavement construction quality to the contractor, they define the desired final product, and they allow the contractor significant latitude in achieving that final product.  This leads to innovation, efficiency, and lower costs.  However, these specifications and their statistical sampling requirements are often too complex and resource intensive to be used at the local agency level.

Performance Specifications

Performance specifications are those in which the product payment is directly dependent upon its actual performance.  Typical of these specifications are warranty, limited warranty and design-build-operate contracts.  Contractors are held responsible for the product performance within the context of what they have control over.  The contractor is given a great deal of leeway in providing the product, as long as it performs according to established guidelines.  In this case, the contractor assumes considerable risk for the level of service the product provides by paying for or providing any necessary maintenance or repair within the warranty period.