Geometry > Approach Geometry > Grade Separation G

Grade Separation G

Grade Separation is not used in the HCM model.

The Grade Separation G is changed from zero to 1 at interchanges on approaches that changes level (either up or down). The capacity line has a larger intercept and is steeper than at normal at grade approaches at intersections. This increases capacity at low circulating flows and reduces capacity at high circulating flows.

The same capacity effects apply to very large roundabouts with inscribed circle diameters greater than 425 ft (130 m). For such roundabouts and for roundabouts terminating freeways G should be set to 1 for all legs disregarding the lack of grade change.

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