Saturday, February 16, 2008

Board from the Back of the Bus (maybe not)

When boarding a tour bus, the driver often tells you to occupy seats at the back of the bus first. This protocol is assumed to be more efficient than filling seats from the front because people block the aisle while stowing their carry-on baggage and thereby impede the flow. So, back-filling is more efficient than front-filling but is it optimal? The same procedure is used by airlines that implement boarding by groups A, B, C, etc. Group A is usually seated at the rear of the aircraft. There are some variants with aircraft boarding (e.g., window seats before aisle seats) that also help to distribute the passenger weight more evenly. The question remains, however, is it optimal?

An astrophysicist recently decided to look into this question more carefully using Monte Carlo simulations and found some surprising results. He unexpectedly discovered that the common rear boarding procedure is actually the second worst procedure, since it is only slightly more efficient than boarding front-to-back! So surprised was he, that at first, he thought there was a bug in his code. Then it became apparent that there was something more subtle going on. MC sims showed that an optimal boarding method was for passengers to board 10 at a time in every other row, since loading luggage requires about two aisles of space. In this way, passengers are either stowing luggage or sitting in their seats, rather than waiting in the aisle, as they do in the other two protocols. Depending on the size of the aircraft, this boarding procedure produces a speed up of 5 to 10 times over the worst case. Of course, disembarking is still LIFO. :-)

I wonder if this result could have applications in the context of computer or network performance analysis and capacity planning?

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