In San Francisco we have toll tags called FasTrak. You can pay for parking at the airport with it. Of course, there, it's just the normal, pretty high airport parking rates, but there's no reason you couldn't use such a tag for enforcing quick free drop offs and pickups with exactly that much precision. Enter the drop/pickup area with your toll tag, if you're out in 3 minutes, no charge. 5 minutes, $4, and if longer than that, $20/hour or whatever. It's not like computers mind doing that math.
In San Francisco we have toll tags called FasTrak. You can pay for parking at the airport with it. Of course, there, it's just the normal, pretty high airport parking rates, but there's no reason you couldn't use such a tag for enforcing quick free drop offs and pickups with exactly that much precision. Enter the drop/pickup area with your toll tag, if you're out in 3 minutes, no charge. 5 minutes, $4, and if longer than that, $20/hour or whatever. It's not like computers mind doing that math.