In an effort to support design and testing activities at product development lifecycle of the engine, proper duty cycle is required. However, to collect data and develop accurate duty cycles, there are not any vehicles equipped with prototype engines at customers. Therefore, in this paper, discrete duty cycle development methodology is studied to generate trailer truck engine usage profile which represents driving conditions in Turkey for engines in development phase. Cycles are generated using several vehicles equipped with prototype engines and professional drivers that can mimic customer usage. Methodology is based on defining real-world customer driving profile, discretizing real-world drives into separate events, collecting vehicle data from each discrete drive, determining the weight of events by conducting customer surveys and creating a representative reference usage profile with data analysis. Duty cycle generation methodology is applied to trailer truck equipped with 10L diesel engine. Time based data from CAN network is recorded, usage profile is generated via discrete approach and developed data analysis tool. When a proper duty cycle is not present, common approach in engine design and verification studies is to use widely accepted emission cycles. To understand effectiveness of emission cycles at design studies, Worldwide Harmonized Transient Cycle (WHTC) is compared with developed usage profile using graphical representations and key metrics. Further analysis conducted to calculate correlation of WHTC with generated usage profile. In addition to results, conclusions are presented on using emission cycles for engine design and verification purposes. Potential applications of discrete cycle methodology are underlined.