Don't Delay

two items: item1(green)
item2(red) it's important, so don't delay


If a car carrying a item(red), any car loading or unloading operations(green) are prohibited to this front car(when the car with item2 can be delay).
At the same time, it's skipped to loading or unloading of the front car.
It will run one circle with item2 to load or unload next.
It is to prevent any blocking to the car with a red item by other cars.

Can I do it by code.
I have a simple model

I say clear to this:

There are two kinds of lots. The first one is green and the other is red.
Red lots are important and we don't want them to delay. When lot is competed process and need to be moved to next step, the dispatching of vehicle is followed by first come first serve. All vehicles are always keeping moving on track, even without any lot need to be moved.

However, if a vehicle is carrying a red lot, any vehicle front of this one in 32 meters is prohibited to load or unload green lot.
The front vehicle can't stop and need to move pass the green lots.

What should I do for setting the situation above?