Comment by SeanLuke | Hacker News Reader

Comment by SeanLuke | Hacker News Reader

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This article mentions Dulles Airport's "mobile lounges", but doesn't explain their extraordinary history, which has absolutely nothing to do with the issues discussed in the article itself. [Dulles has no train connection yet].

If you've gone through DC's Dulles Airport, especially its international terminal, you may have experienced traveling in what must be described as a moving room, a kind of huge, wide bus. Long ago, these things were an experiment in a radical and wonderful 1960s approach to airport design which sadly couldn't work with our modern airport security.

The original design of Dulles airport was a single rectangular building: one huge atrium. There were no terminals at all, no gates at which airplanes parked. Airplanes stayed out on the tarmac somewhere. Instead, the building had an array of what might be best described as garage doors. When your flight was ready, a mobile lounge would drive over to a certain garage door and attach to it. The door would open and everyone on the flight would walk into the lounge. The lounge would then disengage and drive you over to the plane. There, it would lift vertically until it matched the plane door and attach to the plane. You'd then walk into the plane.

[Edit: yes, many european airports drive you out to the plane by bus: but you must still climb the entranceway to the airplane outdoors, and you must enter the bus in, well, traditional bus fashion. With the mobile lounges, it's as if you never went outdoors.]

It was an elegant and simple distributed system. Wikipedia says it failed because it couldn't keep up with passenger numbers: but I think, at least with Dulles Airport's one-single-massive-atrium-building design, it mostly failed because it was completely incompatible with a single-point bottleneck security line (sadly) required at modern airports. So the whole architectural design was doomed to failure. Over the years Dulles has grown terminals and security checks and underground passageways, and the lounges are now relegated to basically being buses between terminals.

I have twice been in a situation where I had to deplane by mobile lounge at Dulles. For your standard modern medium-haul airplane, it takes at least two mobile lounges to fully support the passenger load, and it's a decently crowded standing-room-only affair.

Continuing the original vision, it's clear that passenger counts are absolutely incapable of supporting the "lounge" aspect of the mobile lounge design. You don't want to be on those things longer than you have to. It's still more comfortable than a trek on the tarmac, but it's definitely not superior to the modern gate system.

I’ve been on them a couple of times, an am not sure I would prefer them over a walk on the tarmac.

These things differ from buses in that they are noisier (big engines that probably are old, too, because replacing them is expensive), smellier (I don’t remember whether windows open at all but they have fewer windows per m²), slower (their high center of gravity makes turning more difficult) and don’t give passengers a nice ride (again likely because of their high center of gravity).

Because they take more passengers than regular buses and passengers enter through relatively narrow entries loading passengers also takes longer than with a regular bus. If they used regular buses, the first bus could often already be unloading before the first of these departs.

When I used them, it was easily 15 minutes or so between entering one of these and the start of the ride. You could walk a mile on the tarmac in that time. Certainly in evenings outside Washington’s snowy winter and hot summer, I think I would rather walk.

Just add more lounges? Scale out horizontally?

I watched the video linked in the article, and I am not sure how they are different from buses? They seem to be completely custom built, making them expensive to maintain or of to build newer larger ones.

Edit: I think I realise now that the difference is that you save having to walk up a flight of stairs to the plane, thus you'll never actually be outside. That is neat, but I am not sure it is worth the expense.

Other airports have gates where the plane is somewhere else, and it's just buses picking you up, since the buses arrive like regular buses, they don't have to wait for the other one to reverse out. And since they are just buses, getting more buses is easy, and possibly a lot cheaper.

> but I think, at least with Dulles Airport's design, it mostly failed because it was completely incompatible with a single-point bottleneck security line (sadly) required at modern airports.

MCI (Kansas City) has separate security areas for each handful of gates.

Here's a map showing the general shape of one of the three terminals: https://www.ifly.com/kansas-city-international-airport/MCI-C...

I don't see an online map with the security areas marked, but the way it works is that the outer edge is divided into segments for each few gates, and each segment is separate with its own security.

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For a "mobile lounge" setup, I'd assume each docking area for the lounges would have a security entrance and it ought to work about as well as what MCI has.

Why do you think the"single point bottle neck " was the failure? While I disagree with the need for"modern security " surely you have your single point bottle neck to enter this large room. Once in the room, you are cleared and free to travel in the lounges.

Because Dulles had already been built prior to the need to redesign to provide the single point security design. I think there was no realistic way to add it after the fact and still retain the lounges attaching directly to the massive internal (effectively) one-room building.

Built by the great Finnish-American architect Eero Saarinen.He also designed the St.Louis Arch.

Those things are terrible. I had a tight connection, was first or second in this movable room, and waited for 25 minutes for it to start moving. Then there was a security screening in the place it moved to, for another dozens of minutes. Terrible.

Here’s a wonderful original marketing video [0] in support of the Dulles design.

[0] https://m.youtube.com/watch?v=Oyb4nLFeg5M

> a single-point bottleneck security line (sadly) required at modern airports.

Why could you not replicate the security procedure across all lobbies?

There's effectively two main schools of designing multiple-terminal airports. One school is to design each terminal as a separate island in a vast sea of tarmac, so that all of the inter-terminal transportation has to be done post-security. This is the model of, say, ATL or IAD. The other school is to put all of your terminals around a central cluster such that every terminal can have independent pre-security access. This is what, say, ORD or DFW do.

In the latter setup, each terminal gets independent security lines, but there is often (although, as in DCA, not always!) post-security connections between terminals that allow you to choose any security line you want, although at the potential expense of a lot of extra walking. But in the former setup, there really isn't any alternative to a single security line for everybody. And if you have an airport like IAD where space was never budgeted for that security line in the original terminal construction, it can get pretty bad.

i have seen airports where the security check is per gate. you don't get spikes on those because only the passengers for that particular flight will be in the queue

Presumably, instead of TSA, you'd need TTSA instead (Tens of Thousands Standing Around).

There's a certain minimum staffing level for any TSA checkpoint and the overhead doesn't scale down linearly to checkpoints serving fractions of the lanes today. I don't know what the minimum is, but it seems like it's at least 7 or 8 (1 on ID inspection, 1 on baggage scan, 1 on backscatter, 1 supervisor, 1-2 on baggage manual inspection who could also metal detect/manually inspect wheelchairs, 2 available for "male/female assist", 1 supervisor)

Surges are also better handled by centralizing the checkpoints. Whatever lounge is headed towards flight 123 is going to have a much more spiky load on security than the average of all gates in a current-design airport. If you have a queue at security outside the single lounge, are you really going to close the door and tell everyone in the queue they're missing their flight? Or will you put pressure on security to overlook things to keep things moving (providing an obvious attack vector for adversaries)? Add it all up, average it all out, move it 100 meters away, and a security delay seems more reasonably a passenger fault to arrive early enough.

> have a much more spiky load on security than the average of all gates

That’s a very good point. And, the airport itself has already balanced the departure times for all flights across the airport. Every flight has a pre-assigned departure window, so in theory, when you average all flights, you shouldn’t have (many) peaky surges in passenger load. Or at the very least, they would be predictable.

Hub airports tend to have large departure banks where all the flights arrive, hold, and depart within a certain time frame, for ease of connections. So this isn’t strictly true.

Money?

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