I'll be going back to Seattle Airport tomorrow, and being a green guy I try to use public transportation. I've gotten it down so I can get from Microsoft to Seattle airport in an hour with no traffic, relaxing on the bus and light rail. I'll give the directions, from Microsoft to Seattle, and they work fine in reverse. I have a 12:30 flight to DEN tomorrow, and will try to get to the airport about 11:30.
I have an ORCA Pass, and it works on SoundTransit and King County busses, so I don't have to worry about having the right change for the bus.
To start I take the Sound Transit 545 bus which is an express bus from Redmond to Seattle running about every 15 minutes during commute times. I catch the bus at Microsoft Commons as I can park my car in the Microsoft parking lot. Note: if you don't have a Microsoft parking pass you need to park in the public park and ride lots.
There is a 10:06 or 10:21 bus. I'll get on the 10:06. in 22 min at 10:28. I am at Westlake Center. Go down into Westake Shopping center, then go down to the underground bus area. This is where you will catch the Light rail to Seattle Airport. The end and start of the Light Rail is Westlake and the Airport, so it is easy as end points.
The travel time from Westlake to Seattle Airport is 37 min, and quite frequently I have been lucky waiting only a few minutes and actually make it from Microsoft to the airport in an hour.
Once you arrive at the airport you have a walk from the station to the gates, but not that bad. My 75 year old mother can walk it, and she has a bad knee.
I'll get there a bit early, and if I miss a bus or have to wait, I'll still be at the airport 45 minutes before my flight which should be fine.
Hope this help some of you take the bus from Microsoft to Airport.
I tried Google Maps Public transit feature, but it came up with trips that took 1 1/2 hrs. The trip map look longer on the map, but it is fast given the 545 is an express bus and the Light Rail has priority for traffic signals.
Try it some time, I am sure you'll find it a nice alternative to driving.