Your mention of tailgating reminded me of Barnett Banks of Florida, now part of Bank of America. On their headquarters campus they eliminated tailgating by a) tracking a person's location, b) controlling access in both directions through a door and c) using single person turn styles or rotating doors on all entrances and exits for each campus building. If one got caught someplace where the computer did not have them located, they had to call security to get released. A security infraction was a major black mark for employees and visitors alike.