Conventional intersections are relatively dangerous, with twice the crash rate of a 2-phase intersection. Installing 2-phase intersections on a four-lane road gives it the capacity of a six-lane road, so is cheaper accordingly. Crossovers are preferable because they are more driver friendly, and the extra signal hardware is justified.
Although 2Pi intersections have never been used before Hoddle St, they will have enormous benefits of 70% increase in capacity, half the delay, and half the crashes. This conclusion is widely applicable because because it was tested on 30 of the most difficult sites. They were sketched and modelled in detail to retro-fit 2Pi within their existing footprint and the result was a vast improvement in capacity, delay and alignment for each of them.
Similarly, because of the much shorter clearance distances and fewer phases, the 2-phase DDI has: half the delay; twice the capacity; half the crashes; and fewer gridlocks, compared to a single point interchange.