How early to leave, when the car has to go somewhere first

Somebody dropped at the curb has one number to worry about. Somebody parking a car has four, and two of them happen after the driving is finished.

The four terms

1. 1. Terminal time. How long before departure you want to be at the terminal. Two hours domestic, three international, and there is no clever way around either.
2. 2. The corridor drive. City to a lot in the Millbrae and San Bruno band: twenty to twenty five minutes off peak, forty and up in a bad hour.
3. 3. The shuttle wait. Five to ten minutes through the day. Twenty or more late at night.
4. 4. The shuttle ride. Eight to twelve minutes to the terminals, longer if yours is the last stop on the loop.

Add all four, subtract from departure, and that is when you leave the house.

Worked, for a real morning

A nine in the morning domestic departure, leaving from the west side of the city on a Tuesday, ordinary week.

Nine in the morning minus three hours and twelve minutes is a five fifty departure from home. It feels absurd and it is right, and on the two mornings a year the corridor stops, it is the reason the flight is made.

The parts people leave out

The shuttle wait. Nobody plans for it. It is the single most common reason somebody arrives at the terminal later than they intended after parking off airport, and it costs an average of eight minutes for no reason other than not having counted it.

The loop. Shuttles here run all four terminals. If yours is third, the ride is not twelve minutes, it is eighteen, and knowing which stop you are is worth asking the operator at the gate.

Unloading and the walk to the stand. Three to five minutes on a good day, ten with a family and a stack of bags.

The two hours of the week that break it

Weekday mornings, six to nine, southbound. The corridor drive goes from twenty five minutes to forty five, and it does it without warning on any given day.

Sunday evenings, northbound. Irrelevant on the way out, and the reason a collection that should take half an hour takes an hour.

Neither is avoidable. Both are predictable, which means both belong in the sum rather than in the surprise.

What the desk will do about it

Name the departure time on the reservation form and ask for a drop off hour, and one comes back with a note saying which of the four terms above got stretched to produce it.

If you name a drop off hour yourself, we take it at face value. Somebody will mention it only if the number looks genuinely dangerous, because this is a booking desk and not a nanny.

The one rule

Slack is not padding. It is the only term that absorbs a closed lane, a shuttle that has just left, or a bag that will not close.

Twenty spare minutes are free. Going without them loses somebody a flight every few years, which is a spectacularly bad trade for the time saved.