Regularity tests have to be done thinking of the participants (people who enjoy driving their classic cars) and the safety of road users, who do not be affected by such events.
RallyClassics spent years looking little-traveled roads, and adjusting schedules to maximum support of participants and other users: the most narrow and busy roads should only be done at night, while day use should be wide enough or low-traffic routes.

The success of the 1st Criterium Nocturn Costa Brava is precisely to this: the consciousness of many participants leads them to prefer to spend the night driving but without disturbing others. On mountain roads at night there is a 3% traffic regarding the day, the lights of any oncoming vehicle are, and excursions cyclists or motorcyclists, or illegally parked tourists avoiding to take pictures.