A single point interchange has double the delay of a diverging diamond interchange

Submitted by john on Sun, 15/12/2019 - 19:34
monash toorak interchange

Monash Fwy, Toorak Rd is a single point interchange, previously considered efficient, and having only 3 phases. Note the long existing clearance distances, covering the width of the Freeway underneath, that cause considerable lost time with amber and all-red and these clearances are more likely to fail and be blocked.

But a Diverging Diamond Interchange, as sketched on top, would have a delay cost of only $5,012/hr compared to a delay cost of $11,115/hr for the existing single point interchange, for the same size footprint, using the existing structure. It would better accommodate ramp meter queues.
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.