Theresa Rupel has learned to work a system that was designed to be worked.

The Los Angeles resident visits friends and family in Oak Harbor two to four times a year. Once she steps off the airplane at Sea-Tac, her real trip to Whidbey Island begins. And it costs her about $5.

Between public transportation and ferries — she also has family in Poulsbo — Rupel knows the ins and outs of a relaxing and frugal commute.

“I’ve learned to use the system in both directions,” she said.

Before Rupel leaves L.A. she pulls up the Seattle transit schedule and studies the various routes and times that will help her materialize at the Mukilteo ferry dock.

“I print those, stick them in my pocket, and when I arrive, depending on the time, I choose which route I want,” she said. A full transit schedule awaits her at the airport.

“You only have to walk a few paces to get that.”

Hopping on the bus outside the airport, she pays a nominal fee and, depending on the audibility of her stomach grumbling or her desire to explore Seattle, she tweaks her schedule accordingly, again using the time table residing in her pocket.

“You pay $1.25, which is nothing,” she said. “You usually change in downtown Seattle and then go to the Lynnwood station. It takes three or four buses, depending on the route.”

Less than $5 whisks her from Mukilteo to Clinton, where an Island Transit bus is either waiting or on its way.

“The bus is right there at the door,” the L.A. social worker said. “If it’s not there yet, you have a nice, warm ferry terminal to wait in.”

From Clinton to Oak Harbor takes the seasoned traveler just over an hour, albeit an hour in which she savors every picturesque moment. Reluctantly leaving behind the natural beauty of the commute, Rupel steps off the bus at the Wal-Mart stop and her chariot awaits.

“My friends pick me up there and it’s over,” she said. “It’s a lot of fun and it’s so beautiful. It’s inexpensive and it’s clean, warm and scenic. The bus shelters on Whidbey Island are also very comfortable.”

Rupel first fine-tuned her travel route 15 years ago when she would visit a friend in Poulsbo. The Winslow ferry only charges passengers going from Bainbridge Island to Seattle, remember. When her friend married an Oak Harbor resident, she hatched a new route plan.

“I always plan four hours, but it usually takes less,” she said. “Four hours gives me plenty of time to relax. No stress is good. And the buses always come within minutes of when they say they will.”

With tendrils of bus routes from which to choose and a wide-open schedule, Rupel sets her own itinerary and takes plenty of time to smell the roses — or more accurately, pick the berries.

“Sometimes I spend time on the wharf,” she said. “It’s a great time.”

Even if one did not plan ahead, the resources available at the airport and later at the ferry dock more than suffice.

“It’s so easy, you don’t have to go to the lengths that I do,” Rupel said.

Sunday’s snowfall prompted her friends Deanna and Tom Frederick of Oak Harbor to insist on taking the shuttle. Rather than argue, she acquiesced — under duress.

“I’m having bus transit withdrawals,” she said with a laugh, stubbornly maintaining that she could arrive at Sea-Tac by land in the same amount of time it would take to fly from Oak Harbor, given the inclement weather and erratic schedules implicit with air shuttles.

Under normal circumstances, she would be waving goodbye to her friends from the inside of a cozy Island Transit vehicle.

“It’s just as easy getting back,” Rupel said. “I basically do the same in reverse.”