# How do animated ads in subway tunnels work? **URL:** \ **Category:** Factual Questions\ **Created:** [March 24, 2025, 7:43am UTC](https://boards.straightdope.com/t/how-do-animated-ads-in-subway-tunnels-work/1016013 "2025-03-24T07:43:43Z")\ **Posts on this page:** 12\ **Page:** 1
**Author:** ![Spectre\_of\_Pithecanthropus](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/spectre_of_pithecanthropus/32/12343_2.png) [@Spectre\_of\_Pithecanthropus](https://boards.straightdope.com/u/Spectre_of_Pithecanthropus)\ **Post date:** [March 24, 2025, 7:43am UTC](https://boards.straightdope.com/t/how-do-animated-ads-in-subway-tunnels-work/1016013/1 "2025-03-24T07:43:43Z")
I don’t know how common this type of ad is, but sometime around 2010 I was sitting next to a window on the L.A. subway when this animated ad for the movie _Coraline_ appeared in the window. I think I get the basic idea here. The successive images of the scene are projected onto the walls of the tunnel, and you see them in order as the train speeds past. However, what I don’t understand is why this method of animation works. I thought in order to utilize the persistence of vision effect, each still image has to be kept stationary with respect to the viewer for a split second, before the next image is displayed. Otherwise, as I understand it, we would see a mere blur of images, like when an old-school film is improperly threaded in the projector. Since the train obviously can’t stop 20 times a second or whatever, so the images are still, how do they make this work in a subway tunnel? For those who haven’t seen it, here’s a [YouTube video](https://youtu.be/4ae99OkPlLw?si=46XOMQBdVQAPZLI7). It looks like this is in the DC metro, but I think the ad was rolled out to every subway system in North America. The idea was probably revolutionary at the time, but I don’t think it caught on. ---
**Author:** ![Monty](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/monty/32/47_2.png) [@Monty](https://boards.straightdope.com/u/Monty)\ **Post date:** [March 24, 2025, 8:46am UTC](https://boards.straightdope.com/t/how-do-animated-ads-in-subway-tunnels-work/1016013/2 "2025-03-24T08:46:21Z")
[_Wired_ has a good explanation of how those subway tunnel zoetropes work.](https://www.wired.com/2004/06/zoetrope-subway/) > [@](#): > > "The motion picture technology – actually a long series of still images in slatted boxes – works because a moving passenger perceives the still images seen through slits like a movie projected through a rapidly clicking shutter. The article’s super short, so I just quoted one of the three paragraphs. ---
**Author:** ![Joey\_P](https://avatars.discourse-cdn.com/v4/letter/j/919ad9/32.png) [@Joey\_P](https://boards.straightdope.com/u/Joey_P)\ **Post date:** [March 24, 2025, 12:10pm UTC](https://boards.straightdope.com/t/how-do-animated-ads-in-subway-tunnels-work/1016013/3 "2025-03-24T12:10:13Z")
I had this whole long reply written, mostly trying to understand where the OP’s confusion was coming from. I couldn’t understand why the OP thought strapping a projector to the roof of a subway train would be an issue. Then I read your article. I guess I’m the one that’s confused. I found a video of how this works. It’s using images painted on the subway wall, the ones in the OP’s link must be individually projected images. Same effect though, I think. [![](https://img.youtube.com/vi/m6X9sNau9ok/maxresdefault.jpg "Masstransiscope: A Zoetrope Hidden in an Abandoned NYC Subway Station") ](https://www.youtube.com/watch?v=m6X9sNau9ok&t=1) ---
**Author:** ![Mangetout](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mangetout/32/19_2.png) [@Mangetout](https://boards.straightdope.com/u/Mangetout)\ **Post date:** [March 24, 2025, 12:20pm UTC](https://boards.straightdope.com/t/how-do-animated-ads-in-subway-tunnels-work/1016013/4 "2025-03-24T12:20:03Z")
So it is exactly the same mechanism as the antique drum-type zoetropes, except stretched out in a line. > **[Zoetrope](https://en.wikipedia.org/wiki/Zoetrope)** > > A zoetrope is a pre-film animation device that produces the illusion of motion, by displaying a sequence of drawings or photographs showing progressive phases of that motion. A zoetrope is a cylindrical variant of the phénakisticope, an apparatus suggested after the stroboscopic discs were introduced in 1833. The definitive version of the zoetrope, with replaceable film picture film strips, was introduced as a toy by Milton Bradley in 1866 and became very successful. > The name zoetrope was comp... In the video posted in the OP, the shutter appears to be more like the slats of a venetian blind, so you can only actually see each frame perpendicular to its plane - thus mitigating the smearing you would get if it was just a series of images with no shutter. ---
**Author:** ![RitterSport](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/rittersport/32/6326_2.png) [@RitterSport](https://boards.straightdope.com/u/RitterSport)\ **Post date:** [March 24, 2025, 12:39pm UTC](https://boards.straightdope.com/t/how-do-animated-ads-in-subway-tunnels-work/1016013/5 "2025-03-24T12:39:46Z")
> [@Mangetout](#): > > the shutter appears to be more like the slats of a venetian blind Yes. They had these on the PATH train for a while. Occasionally, the train would slow or stop inside the tunnel and you could see the slats. ---
**Author:** ![pulykamell](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/pulykamell/32/3166_2.png) [@pulykamell](https://boards.straightdope.com/u/pulykamell)\ **Post date:** [March 24, 2025, 1:22pm UTC](https://boards.straightdope.com/t/how-do-animated-ads-in-subway-tunnels-work/1016013/6 "2025-03-24T13:22:02Z")
> [@Spectre\_of\_Pithecanthropus](#): > > The idea was probably revolutionary at the time, but I don’t think it caught on. By 2010, it would have been around for awhile. We had these in Budapest c. 2001. I had wondered whatever happened to them. I’ve never seen it in North America and had no idea they were tried out here for a spell. ---
**Author:** ![DETXL](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/detxl/32/19366_2.png) [@DETXL](https://boards.straightdope.com/u/DETXL)\ **Post date:** [March 24, 2025, 1:48pm UTC](https://boards.straightdope.com/t/how-do-animated-ads-in-subway-tunnels-work/1016013/7 "2025-03-24T13:48:28Z")
San Francisco’s BART also at least tried zoetrope ads—they were there when I moved to SF and I assumed they’d always been there, although apparently it started in 2007. There’s an [example linked in this post](https://community.soulstrut.com/discussion/31339/zoetrope-style-ads-in-the-bart-tunnel) that looks a little janky, although my recollection is that this is true to life and not an artifact of YouTube. I’m not sure they’re still around or, if not, how long the experiment wound up lasting. But at least, for a data point, that’s another American mass transit system that used them. ---
**Author:** ![pulykamell](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/pulykamell/32/3166_2.png) [@pulykamell](https://boards.straightdope.com/u/pulykamell)\ **Post date:** [March 24, 2025, 1:56pm UTC](https://boards.straightdope.com/t/how-do-animated-ads-in-subway-tunnels-work/1016013/8 "2025-03-24T13:56:27Z")
In one of the auto suggested threads, a user mentions them being in Chicago in 2006, so that’s another system. I live here and I guess I wasn’t taking the subway portions of the el enough to see them. ---
**Author:** ![jnglmassiv](https://avatars.discourse-cdn.com/v4/letter/j/f07891/32.png) [@jnglmassiv](https://boards.straightdope.com/u/jnglmassiv)\ **Post date:** [March 24, 2025, 3:54pm UTC](https://boards.straightdope.com/t/how-do-animated-ads-in-subway-tunnels-work/1016013/9 "2025-03-24T15:54:03Z")
Like others said, the slats perform the shutter function to only allow you to see one still image at a time. If we just dragged a length of motion picture film across a projector lamp but without the flickering shutter, we’d get the blur like OP described from transitions between frames. The forward motion of the car keeps telltale parallax down and framerate high enough the pull off the illusion. ---
**Author:** ![FluffyBob](https://avatars.discourse-cdn.com/v4/letter/f/ecb155/32.png) [@FluffyBob](https://boards.straightdope.com/u/FluffyBob)\ **Post date:** [March 24, 2025, 4:10pm UTC](https://boards.straightdope.com/t/how-do-animated-ads-in-subway-tunnels-work/1016013/10 "2025-03-24T16:10:06Z")
I suppose the page transitions in a flip book animation serve this purpose as well. It seems, as in this case, the transition is much less discrete than with a movie projector. The consistency of image elements must be dominate over the blur of movement of curling page transitions or interstitial portions of yhe viewers experience on the train. ---
**Author:** ![Robot\_Arm](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/robot_arm/32/18280_2.png) [@Robot\_Arm](https://boards.straightdope.com/u/Robot_Arm)\ **Post date:** [March 24, 2025, 4:14pm UTC](https://boards.straightdope.com/t/how-do-animated-ads-in-subway-tunnels-work/1016013/11 "2025-03-24T16:14:34Z")
Just for another data point, I saw these on the Boston subway years ago; between Central Square and Harvard, if anyone’s curious. ---
**Author:** ![suranyi](https://avatars.discourse-cdn.com/v4/letter/s/e36b37/32.png) [@suranyi](https://boards.straightdope.com/u/suranyi)\ **Post date:** [March 24, 2025, 4:46pm UTC](https://boards.straightdope.com/t/how-do-animated-ads-in-subway-tunnels-work/1016013/12 "2025-03-24T16:46:38Z")
They had an ad like this on the Montreal Metro between Peel and McGill stations back in the 70s. So it’s definitely not new. I even remember what it was advertising: Direct Film, a long-defunct photo store.