This is a trapezoidal FD consisting of a free flow, congested branch + a capacity line. When the capacity line causes a restriction below the intersection point of the free flow and congested branch on the flow density plane, it results in a trpezoidal shape, otherwise it reverts to a triangular shaped. This is more realistic than a triangular FD where for high speeds the inferred capacity is likely too high.
This is a trapezoidal FD consisting of a free flow, congested branch + a capacity line. When the capacity line causes a restriction below the intersection point of the free flow and congested branch on the flow density plane, it results in a trpezoidal shape, otherwise it reverts to a triangular shaped. This is more realistic than a triangular FD where for high speeds the inferred capacity is likely too high.