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CONSULTING ENGINEERING 29 Over the years, engineering experience has established some approximate correlations between engineering costs and construction costs, for certain types of engineering design, where design procedures and materials of construction are more or less standardized. These correlations have resulted in various curves and schedules which have been widely used - so much so that they are sometimes mistakenly regarded as fixed bases of compensation for design projects of any kind. The validity of the percentage-of-construction-cost method rests upon the assumption that engineering costs vary in proportion to the cost of construction, irrespective of the location or type of construction undertaken. This is a ques- tionable 'assumption; however, it is not intended to imply that these assumed relationships between engineering costs and construction costs are no longer of value. When judiciously applied, and with the due consideration of the ranges within which engineering scope may vary, they remain valuable as tools for general comparison with lump'sum or salary-plus-multiplier charges for design services. Their acceptance over many years also affords a valuable guide for judging the reasonableness of proposals for engineering services. Many design assignments are negotiated by means of two or more of the foregoing methods of compensation. Quite frequently the preliminary phase of the assignment may be undertaken for a fixed lump sum, especially where the resultant report may be required to establish the project's feasibility, or where the preliminary phase will involve planning for deferred stages of construction. In such cases, the compensation for the preliminary and design phases is combined as a proportionate part of the percentage charge from the curves, and a pro-rata credit allowed for lump-sum payment for the preliminary phase. In other cases, the preliminary phase may be undertaken separately, on the basis of salary cost times a multiplier, and the design and construction phases computed from curves, with appropriate reduction of the percentage compensation. The curves presented in Figs. I and 2 represent median compensation, com- puted as a percentage of "construction cost," necessary to permit Consulting Engineers in the United States to serve their Clients with the degree of technical competence demanded by modern engineering standards. The curves reflect the composite experience and judgment of Consulting Engineers throughout the United States developed from responses to a detailed questionnaire sent out by the Society in 1974 to 2,089 consultants. Obviously, the appropriate compensa- tion for a given assignment may vary above or below the curves shown in Figs. I and 2, depending on the various factors which have been discussed in the forego- ing sections. While these curves may be an appropriate basis for initiating discussions with a client, the final compensation should bedetennined by negotiation following detailed discussion of the scope of services and the elements of the cost of engineering.