The Truck Design Optimization Program (TDOP), Phase I, Frequency Domain Model (FDM) is reviewed. The review of this railcar structural dynamics program is divided into three areas: (1) solution method, (2] Power Spectral Density, and (3) integrity of the excitation function. It is recommended that users exercise judgement and monitor selected parameters to ensure valid results. See also: Vol. I - Executive Summary, FRA/ORD-78/12.I Vol. II - Phase I Final Report, FRA/ORD-78/12.II Vol. Ill - Phase I Frequency Domain Model, FRA/ORD-78/12.III Vol. V - Critique of Frequency Domain Model - Equations of Motion, FRA/ORD-78/12.V Vol. VI - Critique of Phase I - Test Series Results Reports, FRA/ORD-78/12.VI Also available in microfiche or photocopy form from NT IS: Vol. VII - Results Report for Test Series I, FRA/ORD-78/12.VII Vol. VIII- Results Report for Test Series 2 and 5, FRA/ORD-78/12.VIII Vol. IX - Results Report for Test Series 4, FRA/ORD-78/12.IX Vol. X - Results Report for Test Series 3 and 5, FRA/ORD-78/12.X Vol. XI - Performance Guidelines for Type I Trucks FRA/ORD-78/12.XI Vol. XII - TDOP Postprocessing Program Manual, FRA/ORD-78/12.XII 18