So I feel like non- Islanders just don't quite get how transit on and off the Island works here. SO here's how it goes.
Washington State Ferry
The primary way that people get on and off Vashon Island is through the Washington State Ferries. These ferries, operated by the State are for: walk on passengers, automobiles, trucks, motorcycles and leashed pets (though they are only allowed on the car deck. They run very frequently and wait is not usually very long (the pattern during the day seems to be 20min.20min.40min). There are Washington State Ferry docks at the North End of Vashon Island and at the South End of Vashon Island (Talequah-Pt. Defiance/Tacoma). For this post I will only discuss the north end transit options as those are the ones in and out of Seattle.
Every once in awhile there are quirks with the ferries. Sometimes a boat is broken or enough crew members are sick that the boats don't run as frequently. Then they revert to a two boat schedule. This has only happened a handful of times this year. One was Christmas Eve, we waited for hours and hours! It also happened Sept. 7- I only remember the date because we had a housewarming party at the time. I know there were a couple of others but it wasn't that relevant to us.
The Washington State Ferry from the North End of Vashon goes to a road in Seattle called Fauntleroy which is in the West Seattle Neighborhood- in fact I think that the neighborhood is actually called Fauntleroy as well. This is key to know! Fauntleroy is West Seattle! West Seattle, depending on the time of day is at least 20 minutes from downtown and at rush hour can be over an hour in your own car.
You can also take the bus- the red line- too and from downtown Seattle the the ferry dock. That take awhile but it very convenient, as it drops off in the heart of the city. There are a couple of other buses that run from downtown to Vashon, I have only ever taken the 116 from downtown and it drops off right at the dock as well.
You do NOT have to pay to leave the Island on the Washington State Ferry. Because it is pretty much the only way on and off the Island they just double charge when you go TO the island. The fees can be hefty to get to the Island. As Islanders we buy a 10 ride pass and it is a bit cheaper. It is definitely part of the cost of living though. To just walk on to Vashon Island it is about 5 bucks for an adult. Oh, little kids ride free too. That's handy!
There is another option to get to Downtown, which is what I take almost daily. This is called the King County Water Taxi. The water taxi is a passenger only (and bikes too) boat. It is sometimes called the P.O. This hold about 150 people and departs Vashon/Seattle 3 times in the morning and 3 times in the evening. It takes passengers from Vashon to right downtown. Many people who ride it work downtown or others like me hop a quick bus to nearby locations. The 5:30pm boat sometimes fills and they have to send people away. I'm sure it happens other times as well but my instinct is that is the most frequent boat to fill.
In evening you line up along the dock and then board accordingly. Almost everyone has an Orca card to board the boat- but both docks in Seattle and on Vashon allow you to purchase a pass or you can pay cash as you board. Many people take bikes on this boat. They are the last to unload at the arriving dock. Buses on Vashon drop people off in the AM about 10 minutes before the PO leaves and pick up the evening as well. Frankly it is hella convenient. The ride on the PO boat is just over 20 minutes to downtown- assuming the weather is normal and such!
The problem with the PO at this point is that it breaks down with some frequency. They are building a new one that is bigger- but at this point it runs like a used car. Kinda reliable, mostly reliable, but a bit wonky at times.
Parking on Vashon
So on another note is parking on Vashon. There is a short term and a long term (two weeks) parking lot that are a short walk (up/down hill) from the ferry. It is max a 10 minute walk. Because we now take the bus we don't utilize this anymore, but last year we were driving every morning and there was always parking. We have also parked our car in the long term for a week or so while on a trip. Pretty handy I must say!
All in all, it works out smoothly more than not!
Are there other things I should address? Seems like you, reader, probably know the questions you have!