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Model Development to Predict Free Flow Speed for Multi-Lane Highways

Dr. Ahlam K Razzaq

As defined in the Highway Capacity Manual HCM, Free flow speed (FFS) is” an average speed of vehicles on a given segment, measured under low-volume conditions, when drivers are free to travel at their desired speed and are not constrained by the presence of other vehicles or downstream traffic control devices. It is a parameter which has being utilized widely for limit and level-of-service investigation of different highway classifications. This research concerns collections and analyses free-flow data at the midpoints of forty-two multilane rural and suburban highway segments all through Al-Najaf city. Thus in order to predict FFS from corresponding collected values a, an extremely tests create model for evaluating normal free-low speed and for recognizing the appropriation of individual free-flow speeds. The most crucial variables that oversee FFS are vehicle type, space mean speed, and functional classification of highway. The subsequent models encourage the FFS rates of suburban and rural roadways. The Highway Capacity Manual (HCM- 2000) uses concentration approach to draw from its passenger-car equivalent factors (PCE) for heavy cars. These PCEs emerge like “ET” in HCM charts where ET is 1.5 for all urban highways and rural highways in level terrain. The harmonized traffic has being presumed by the density method and at the same time it has being typified by firm track system. By using the density method, it becomes possible to obtain more precise passenger car unit factors for Iraqi circumstances. The traveller vehicle unit factor (PCU) for trucks and buses is 2.0 in level terrain.