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You can set a fixed travel time (5 minutes, 15 minutes, 30 minutes, etc.) for any appointment. But... if Maps can determine the appointment's location, you'll get additional options for driving or walking based on current location, and the ability to set an optional starting location.

Once travel time has been set for an appointment, you can set alerts based on the start of Travel Time (at start of travel time, 5 minutes before travel time, 30 minutes before travel time, etc.), instead of, say, 30 minutes before the start time of the appointment.

For those appointments, both the iOS and OSX calendar apps will show the padded travel time above the appointment in daily or weekly view. In daily view it is labeled with a car/walking icon and the amount of travel time.

Frankly, I have no idea why Apple has been reticent to tell people about travel time when they've obviously put so much effort into designing it -- for both iOS 8 and Yosemite. It's my favorite new "it just works" feature, at a time when so much of their stuff doesn't. Reminds me of the old days.

I like this feature and use it a lot.

One proviso, though: I like to create events from emails, so as to have a link to the email in the event. However, it's important not to set the travel time from within Mail, at least on iOS. If you do, the location will disappear when you open Calendar. So you must create the event, then go to Calendar to add the travel time. Just one of many bugs that need fixing.
 
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