I wouldn't be as concerned with number of reservations per road quite yet. Reserve the road you want. The ultimate question is the total number of units. Scott makes a call on how low he is willing to go on a specific road name to make the total project go.
It took 5 years to get the Amfleet project to go forward, so don't give up hope. If you are on the fence to order a unit go ahead and place your pre-order. Once the reservations start to show a sign of life, the project can then go into formal design.