The Door Close Button

This will probably be a short one, and I know I haven’t written for a while,
but it has always been the case that you get what you pay for and Computers
Are Bad is nothing if not affordable. Still, this is a topic on which I am
moderately passionate and so I can probably stretch it to an implausible
length.

Elevator control panels have long featured two buttons labeled “door open” and
“door close.” One of these buttons does pretty much what it says on the label
(although I understand that European elevators sometimes have a separate “door
hold” button for the most common use of “door open”). The other usually doesn’t
seem to, and that has lead to a minor internet phenomenon. Here’s the problem:
the internet is wrong, and I am here to set it right. This works every time!

A huge number of articles confidently state that “80% of door close buttons do
nothing.” The origin of this 80% number seems to be a 2014 episode of Radiolab
titled “Buttons Not Buttons,” which I just listened through while doing
laundry. Radiolab gets the statistic from the curator of an elevator history
museum, who says that most of them “aren’t even hooked up.” This is reason to
doubt our curator’s accuracy. I don’t think there is anything malicious going
on here, but I do think there is an element of someone who has been out of the
industry for a while who is at least misstating the details of the issue.

The problem is not unique to Radiolab, though. An Oct. 27, 2016 New York Times
article, “Pushing That Crosswalk Button May Make You Feel Better, but…,”
covers the exact same material as the Radiolab article a couple of years later.
And the article was widely repeated in other publications, not by syndication but
by “According to the New York Times…” paraphrasing. This means that often the
repetitions are more problematic than the original, but even the original says:

But some buttons we regularly rely on to get results are mere artifices –
placebos that promote an illusion of control but that in reality do not work.

Many versions of the article lean on this line even harder, asserting that
door close buttons in elevators are installed entirely or at least primarily
as placebos. But the NYTimes article provides brief mention of the deeper,
and less conspiratorial, reality:

Karen W. Penafiel, executive director of National Elevator Industry Inc., a
trade group, said the close-door feature faded into obsolescence a few years
after the enactment of the Americans With Disabilities Act in 1990.

…

The buttons can be operated by firefighters and maintenance workers who have
the proper keys or codes.

There are a few things to cover:

First, anyone who says that the “door close” buttons in elevators are routinely
“not even hooked up” shouldn’t be trusted. The world is full of many elevators
and I’m sure some can be found with mechanically non-functional door close
buttons, but the issue should be infrequent. The “door close” button is
required to operate the elevator in fire service mode, which disables automatic
closing of the doors entirely so that the elevator does not leave a firefighter
stranded. Fire service mode must be tested as part of the regular inspection of
the elevator (ASME A17.1-2019, but implemented through various state and local
codes). Therefore, elevators with a “door close” button that isn’t “hooked up”
will fail their annual inspections. While no doubt some slip through the cracks
(particularly in states with laxer inspection standards), something that
wouldn’t meet inspection standards can hardly be called normal practice and the
affected elevators must be far fewer than 80%.

But perhaps I am being too pedantic. Elevator control systems are complex and
highly configurable. Whether or not the door close button is “hooked up” or not
is mostly irrelevant if the controller is configured to ignore the button, and
it’s possible that some of these articles are actually referring to a
configuration issue. So what can we find about the way elevators are configured?

I did some desperate research in the hopes of finding openly available
documentation on elevator controller programming, but elevator manufacturers
hold their control systems very close to their chests. I was not lucky enough
to find any reasonably modern programming documentation that I could access.
Some years ago I did shoulder-surf an elevator technician for a while as he
attempted to troubleshoot a reasonably new two-story ThyssenKrupp hydraulic
that was repeatedly shutting off due to a trouble code. In the modern world
this kind of troubleshooting consists mostly of sitting on the floor of the
elevator with a laptop looking at various status reports available in the
configuration software. The software, as I recall, came from the school of
industrial software design where a major component of the interface was a large
tree view of every option and discoverability came in the form of some items
being in ALL CAPS.

The NYTimes article, though, puts us onto the important issue here: the ADA.
Multiple articles repeat that door close buttons have been non-functional since
1990, although I think most of them (if not all) are just paraphrasings of this
same NYTimes piece. The ADA is easy to find and section 4.10 addresses elevators.
Specifically, 4.10.7 and 4.10.8 have been mentioned by some elevator technicians
as the source of the “door close” trouble. With some less relevant material
omitted:

4.10.7* Door and Signal Timing for Hall Calls

The minimum acceptable time from notification that a car is answering a call
until the doors of that car start to close shall be calculated from the
following equation:

T = D/(1.5 ft/s) or T = D/(445 mm/s)

where T total time in seconds and D distance (in feet or millimeters) from a
point in the lobby or corridor 60 in (1525 mm) directly in front of the
farthest call button controlling that car to the centerline of its hoistway
door (see Fig. 21).

4.10.8 Door Delay for Car Calls

The minimum time for elevator doors to remain fully open in response to a car
call shall be 3 seconds.

Based on posts from various elevator technicians, it’s clear that these ADA
requirements have at least been widely interpreted as stating hard minimums
regardless of any user interaction. In other words, the ADA timing constitutes
the minimum door hold time which cannot be shortened. Based on the 4.10.7
rule, we can see that that time will be as long as ten seconds in fairly normal
elevator lobbies (16 feet, or about two elevators, from door centerpoint to
furthest button). We can read the same in a compliance FAQ from Corada, an ADA
compliance consulting firm:

User activation of door close (or automatic operation) cannot reduce the
initial opening time of doors (3 seconds minimum) or the minimum door signal
timing (based on 1.5/ ft/s travel speed for the distance from the hall call
button to car door centerline).

One point here can be kind of confusing. The minimum time for the door to be
fully open is 3 seconds, but the door signal timing is based on the time from
the indication of which elevator has arrived (usually a chime and illuminated
lamp) to the time that the doors start closing. This will be at least a couple
of seconds longer than the minimum door time due to the open and close time of
the door, but since it starts at 5 seconds and goes up from there it will
usually be the longer of the two requirements and thus set the actual minimum
door time. Where this is likely to not be the case are single-elevator setups
where the 5 second minimum timing will apply and the time from chime to door
open eats up the first two seconds… in that case, the 3 second fully open
time will become the limiting (or really maximizing) factor.

From some elevator manuals such as one for the Motion Control Engineering
VFMC-1000, we can gather that that the “minimum door hold time” and “door hold
time” are separately configurable. I have seen several mentions online that in
most elevators the “door close” button functions totally normally during the
difference between the minimum door hold time and the door hold time. In
other words, there may be some period during which pushing the door close
button causes the door to close, but it will be after the end of the
ADA-required minimum door time.

Here is the obvious catch: since reducing the door hold time will make the
elevator more responsive (less time on the way to a call spent waiting with
the doors open), elevator installers are usually motivated to make the door
hold time as short as possible. Since the ADA requirements impose a minimum,
it’s likely very common for the minimum door hold time and the “normal” door
hold time to be the same… meaning that the window to use the “door close”
button is zero seconds in duration.

We can confirm this behavior by finding an elevator with a very long configured
door hold time. That seems pretty easy to do: visit a hospital. Most hospitals
set the door hold time fairly high to accommodate people pushing hospital beds
around, so the normal door open time is longer than the ADA requirement (the
ADA rules are of course written assuming a person can cover 1.5 ft/s which
isn’t very fast but still seems hard to achieve when accelerating a heavy
hospital bed in a tight space). Call an elevator, step inside, wait for around
ten seconds from the chime for the minimum door hold to elapse, and then push
the “door close” button. What happens? Well, in my experience the door promptly
closes, although I admit that I’ve only tested this on two hospitals so far.
Perhaps your experience will vary: I can see the possibility of a hospital
setting the minimum door hold time high, but of course that would get pretty
annoying and probably produce pushback from the staff. In the hospitals where
I’ve studiously observed the elevators the normal door hold time was close to
20 seconds, which feels like an eternity when you’re waiting to get up one
floor.

Another way we can inspect this issue is via door reopening rules. While older
elevators used a rubber bumper on the door called a sensitive edge, most
elevators you’ll see today use a “light curtain” instead. This device,
installed between the hall and car doors, monitors for the interruption of
infrared light beams to tell if the door is clear. When the door is obstructed,
ADA 4.10.6 requires the door to remain open for at least 20 seconds. After that
point ADA just refers to the ASME A17.1 standard, which allows for a behavior
called “nudging” in which the elevator controller encourages people to clear
the door by closing it anyway (at slow speed). The light curtain can also be
used to detect whether or not a person has entered the elevator, which can be
used as an input to hold time. Some articles online say that you can “hack” an
elevator waiting at an empty floor (because someone called the elevator and
walked away, for example) by momentarily interrupting the light curtain so that
the controller will believe that someone has entered.

Indeed this seems to work well on some elevators, but the ADA requirements do
not allow an exception to minimum hold times based on light curtain detection.
This means that the light curtain trick is basically equivalent to the door
close button: we can expect it to, at most, shorten the door hold time to the
ADA minimum. Nothing is allowed to decrease the time below the ADA minimum,
except when the elevator is in a special mode such as fire or perhaps
independent service.

So it seems that the reality of elevator “door close” buttons is rather less
dramatic than Radiolab and the NYTimes imply: the “door close” button is
perfectly functional, but details of the 1990 ADA mean that most of the time
people are pressing it the elevator controller isn’t permitted to close the
door due to ADA rules. As far as I can tell, outside of the ADA minimum door
time, door close buttons work just fine.

And yet tons of articles online still tell us that the button is installed as a
placebo… something that is demonstrably untrue considering its significance
in fire (and maintenance, independent, etc) modes, and shows a general lack of
understanding of elevator codes and the ADA. Moreover, it seems like something
you would find out is untrue with about five minutes of research. So why is it
such “common knowledge” that it makes the rounds of major subreddits and minor
local news websites to this day?

No doubt a large portion of the problem is laziness. The “placebo” theory has a
lot of sizzle to it. Even though the NYTimes is somewhat noncommittal and only
implies that it is the true purpose of the button, most of the online pieces
about door close buttons I can find appear to be based solely on the 2016
NYTimes article and actually repeat the claim about the placebo affect more
strongly than the NYTimes originally makes it. In other words, the “fact” that
the door close button is a placebo seems to mostly just be a product of lazy
journalists rewriting an NYTimes piece enough to not feel like plagiarists.

There is also a matter of aesthetic appeal: the placebo theory sounds great. It
has the universal appeal of mundane reality but also hints at some kind of
conspiracy to deceive in the elevator industry. And, of course, it makes
everyone feel better about the high failure rate of mashing the “door close”
button without the complexity of an accurate explanation of the 1990 ADA rules.
The NYTimes piece basically makes it sound like the ADA banned door close
buttons, and it’s easy to read the ADA and see that that’s not true… but it
takes some real attention and thought to figure out how the ADA really did
change elevator controls.

This type of phenomenon, a sort of “internet urban pseudo-legend,” is not at
all unique to elevator buttons. In fact the very same 2016 NYTimes article
that started that year’s round of elevator button “fun facts” is also to blame
for another widespread belief in placebo buttons: crosswalk request buttons.
The NYTimes article says that most crosswalk buttons do nothing, explaining
that the buttons were made non-functional after an upgrade to computer light
controls. What the article does say, but many readers seem to miss, is that
this is a fact about crosswalk buttons in New York City.

Many traffic lights operate in “actuated mode,” where they base their cycling
on knowledge of who is waiting where. Older traffic lights mostly used buried
inductive loops under the lanes to detect lane occupancy (that a vehicle is
present), but a lot of newer traffic lights use either video cameras or compact
radar sets. Since they don’t require cutting into the pavement and then
resealing it, these are cheaper and faster to install. Newer video and radar
systems are also better at detecting cyclists than pavement loops—although
earlier video systems performed very poorly on this issue and gave video lane
presence detection a bad reputation in some cities.

New York City, though, was a very early adopter of large-area computer control
of traffic lights. One of the main advantages of central computer control of
traffic lights is the ability to set up complex schedules and dynamically
adjust timing. Not only can centrally-controlled traffic lights operate in
sequence timing matched to the speed limit of the street, they can also have
the durations in different directions and sequence speed adjusted based on
real-time traffic conditions.

The problem is that combining central timing control with actuated operation
is, well, tricky. In practice, most traffic lights that operate under sequence
timing or remote timing control don’t operate in actuated mode, or at least not
at the same time. What some traffic lights do today is switch: sequence timing
during rush hour, and actuated mode during lower traffic. Even with today’s
developments combining scheduled timing with actuation inputs is tricky, and
New York City adopted centralized control in the ’70s!

So New York’s adoption of central control was also, for the most part, an
abandonment of actuated operation. The crosswalk buttons are actuation inputs,
so they became non-functional as part of this shift. The 2016 NYTimes article
explained that the city had estimated the cost of removing the now
non-functional buttons at over a million dollars and so decided to skip the
effort… but they are removing the buttons as other work is performed.

For the second time, this runs directly counter to the “mechanical placebo”
argument the article is based on. The buttons weren’t originally installed as
placebo at all; when they were put in they were fully functional. A different
decision, to switch to centralized timing control, resulted in their current
state, and even then, they are being removed over time.

Moreover, the same does not apply to other cities. The NYTimes makes a very
lazy effort at addressing this by by referring to a now-unavailable 2010 ABC
News piece reporting that they “…found only one functioning crosswalk button
in a survey of signals in Austin, Tex.; Gainesville, Fla.; and Syracuse.” It is
unclear what the extent of that survey is, and I lack the familiarity with
traffic signaling in those cities to comment on it. But in a great many cities,
most of them in my experience, actuated traffic signals remain the norm outside
of very high-traffic areas, and so the crosswalk buttons serve a real purpose.
Depending on the light configuration, you may never get a “walk” signal if you
don’t press the button, or the duration of the “walk” signal (prior to the
flashing red hand clearing time) may be shorter.

Actually one might wonder why those crosswalk buttons have so much staying
power, given the technical progress in lane presence detection. Video and radar
options for waiting pedestrian detection do exist. I have occasionally even
seen PIR sensors installed for this purpose in suburban areas. The problem, I
think, is that detecting a pedestrian waiting to cross involves more nuance
than a vehicle. Sidewalks don’t have lane lines to clearly delineate different
queues for each movement. A video or radar-based system can detect a pedestrian
waiting on the corner, but not whether that person is waiting to cross one
direction, or the other, or for an Uber, or just chose that spot to catch up on
Tik Tok. Video-based waiting pedestrian detection may be too prone to false
positives, and in any case the button is a robust and low-cost option that can
also be used to meet ADA objectives through audible and tactile announcements.

So there’s a story about buttons: the conspiracy about them being placebos is
itself a conspiracy to get you to read articles in publications like “Science
Alert.” Or maybe that’s just an old tale, and the reality of content-farmed
news websites falls out of some implications of the ADA. It’s a strange world
out there.