raedarum transitus arto vicorum in flexu et stantis convicia mandrae eripient somnum Druso vitulisque marinis.
"The continual traffic of carriages in the narrow twisting streets and the swearing of the drover when his herd has come to a halt would deprive a Drusus or the seals of sleep." (translated by S. Morton Braund)
Sen. Clem. 1.6:
Certainly, ius indicates the right to take some sort of action, so I should think that either ius itineris ('right of route') or ius transitus ('right of crossing') would be generally suitable as a traffic instruction (and, being more direct and powerful, preferable to using facultas, another possibility).
For the party conceding right of way, transitum ...