One of the more interesting highway behaviors I have seen was a huge backup on a 2 lane highway where truckers would block both lanes and prevent people from passing them. It's a slight cost the each trucker on the left but it significantly increased throughput.
In the blogs example one person 1 goes Start to A, then while person 1 goes B to end Person 2 goes start to A. etc. Worst case travel time is now faster after adding the new road and 2 agents can help this happen by limiting how fast people enter A.
Edit: with 2 people limiting traffic they can reduce their travel time by 25% (3x 1/2 vs 2 x 1) even if they are in the second group. 1/2 the cars do the first leg, then the other half do the first leg while the first set does the second leg.
In the blogs example one person 1 goes Start to A, then while person 1 goes B to end Person 2 goes start to A. etc. Worst case travel time is now faster after adding the new road and 2 agents can help this happen by limiting how fast people enter A.
Edit: with 2 people limiting traffic they can reduce their travel time by 25% (3x 1/2 vs 2 x 1) even if they are in the second group. 1/2 the cars do the first leg, then the other half do the first leg while the first set does the second leg.
PS: This is why we make traffic lights.