numVehiclesIdle

How many vehicles carry no task: idle to the dispatcher.

Not the same question as the space layer's numTransportersIdle, which counts vehicles standing still, and the two rows appear together on an active model's report. A vehicle repositioning to its home base is the case that separates them: it is moving, so it is not idle in the space layer's sense, and it carries no task, so it is idle in this one. Each row uses the word of the layer that owns it -- transporter for the shared space, vehicle here -- because renaming either would make the shared layer speak one consumer's dialect.