Sunday, December 26, 2010

Decision Analysis and Airport Transportation

I flew out of Seoul the other day, and had an interesting lesson in decision analysis and making tradeoffs with respect to airport transportation. The options for getting to the airport from Gangnam are the following:

1) Taxi. Never done it. Pros: Door-to-door. Cons: At the mercy of Seoul traffic (especially bad since I had to travel during rush hour to the airport), and rather expensive.
2) Taxi to Coex, then direct airport bus from City Air Terminal. Pros: Direct bus is a known quantity and cheap (15000). Cons: Taxi still has to fight rush hour traffic in a busy area.
3) Subway to Coex, then direct airport bus. Pros: Both are known quantities and cheap. Cons: Need to lug stuff down into subway and then all the way through Coex to the City Air Terminal.
4) Airport Limousine Bus from nearby stop. Pros: Cheapest option. Cons: Need to wait outside for the bus.
5) Subway the whole way. Never done this, but I think it takes forever and has a bunch of transfers.

Usually I do option 2 or 3, depending on how much luggage I have. But this time I decided to try the Airport Limousine Bus, cause there's a stop about a five minute walk from my place.

I get to the stop, and the sign says the bus comes every 10-20 minutes. Not bad, I think to myself, despite the approximately freezing temperature outside. 5 minutes pass. No bus. 10 minutes. No bus. 20 minutes. No bus. After 30 minutes, 50% more than the maximum interval between busses, still no bus (although I saw two going the other direction), I decided to cut my losses, head to the subway, and go for option 3. Probably an hour wasted, but I'd at least make it to the airport in time.

Of course, when I get about 50 feet away from the bus stop, the bus comes. I try to flag him down, but Seoul bus drivers are friggin' maniacs, and he blew by me and didn't even pause at the bus stop. Fuuuuuuuuuuuuu.

Anyway, while I was standing on the nice warm subway, I considered what had happened. Assuming "10-20 minutes" means a bus comes an average every 15 minutes, then the expected wait time should be 7.5 minutes. Which means I stood out in the cold for four times the expected wait time, or three times the expected wait time if "10-20 minutes" actually means "every 20 minutes". Considering that the airport limousine bus had a bunch of stops before heading to the airport, it probably would have taken like 15-20 minutes more than the airport bus from Coex. Walk to the subway is 5 minutes, then subway to Coex about 7 minutes, then another 7 minutes to get to the City Air Terminal. And the City Air Terminal busses are every half hour, giving an expected wait time of 15 minutes. So the "subway plus City Air Terminal" option has an expected wait time of about 5+7+7+15=34 minutes, and only five of that is out in the cold. Meanwhile, the airport limousine bus has the 5 minutes in the cold to walk to the stop, 7.5-10 minutes expected wait time in the cold, with a "worst-case" wait time of 20 minutes, which I exceeded by 10 minutes anyway. Plus an extra 15-20 minutes on the bus compared to the CAT bus. So the total amount of time for the two options is about the same, except one option has a lot of standing out in the cold, and the other has a bunch of lugging around luggage.

Point of the story is that I waited too long for the bus, and I should have gone with the known quantity from the outset.

No comments:

Post a Comment