$\rho$ is not a universal symbol for traffic intensity. If you do not tell us what it means, it is just a Greek letter. Here are some other ways that it can be used:

Uses of $\rho$.

Unfortunately, I do not know enough about queuing theory to be able to help. I am not understanding your question. What are $p_0$ through $p_5$? Is that the probability that planes 0 through 5 make it to the main concourse? Note: If these are probabilities of planes being serviced in the main concourse, then $p_6$ would be the 7th plane since you used a zero index.

I do not see why the sum of the probabilities would be 1. These are not discrete events. If all five loading docks happen to be empty at the exact same time, then the probability of the next five arrivals getting serviced at the main concourse will be 1 for each. If only one could possibly be serviced at a time, this would be a completely different problem.