For time efficiency, and low CO2, as many people as possible should get priority entry. The practical limit to this is probably 90%.
Assuming we have not yet installed 2-phase at Victoria St, with no queue jumping except for the bus, all traffic takes 25 minutes. But if priority vehicles jump the queue and take only 8 minutes, for a toll, then the free entry vehicles take 41, 44, or 46 minutes for 50%, 70% or 90% jumping respectively, demand then decreases from 5,300 to 5,100, 4,800, and 4,600 respectively, and the queue length decreases significantly. Average trip times for all traffic are 25, 16, 13, and 10 minutes respectively, so 90% is the best outcome. Priority trip time drops from 25 minutes to 8 minutes with queue jumping, saving 17 minutes, but the free access queue trip time increases, with an apparent saving of 38 minutes for queue jumping, so the toll might have to be $3 while there is no 2Pi at Victoria St.