[HN Gopher] The Mathematics of Escalators on the London Undergro...
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The Mathematics of Escalators on the London Underground (2013)
[pdf]
Author : carschno
Score : 81 points
Date : 2022-06-27 08:32 UTC (2 days ago)
(HTM) web link (www.raeng.org.uk)
(TXT) w3m dump (www.raeng.org.uk)
| heavenlyblue wrote:
| Why do those mathematical arguments about CO2 emitted never
| include how much CO2 would be emitted by a person (and
| transitively emitted, too - i.e. how much CO2 would be required
| to produce the required food for the person) if they did the job
| themselves?
|
| I.e. somehow walking 100 steps suddenly produces 0 CO2. Which is
| completely not true, at least in this case the person would be
| breathing, let alone spending calories walking up the stairs.
| rhn_mk1 wrote:
| It's probably because human fuel is in the most part obtained
| by solar power sequestrating carbon from the atmosphere.
| heavenlyblue wrote:
| Does that mean that if I eat meat it may be more beneficial
| to travel by car because a vegetarian is 1000 times more
| efficient than a car vs a non-vegetarian who is only 200
| times more efficient than a car? (numbers are made-up)
| rhn_mk1 wrote:
| If you eat meat, it may be more beneficial to become a
| vegetarian.
| lovemenot wrote:
| Because humans, trees, living things in general are carbon
| neutral over a pretty short duration.
|
| The overwhelming concern is carbon that was newly put into the
| atmosphere from fossil fuel sources comprising millions of
| years' worth being released all at once (less than 200 years).
| Carbon that was recently removed from the atmosphere by plants
| which were subsequently consumed and reintroduced into the
| atmosphere is a very minor concern.
|
| It's not that your perspective is wrong, just that it is
| dwarfed by many orders of magnitude, in respect to fossil
| fuels.
| loonster wrote:
| For every unit of food, there is a unit of oil to produce
| food. I'm not sure what the ratio would be, but it surely
| must be there.
| lovemenot wrote:
| What you say is right. And I realise that heavenlyblue is
| saying much the same. It seems to be about where to account
| for the emissions.
|
| I suppose walking in a foreign city is not accounted
| because agricultural production, transport, hospitality
| etc. already is accounted elsewhere.
|
| There's surely a need to join up all the accounting up
| though.
| heavenlyblue wrote:
| If instead of flying somewhere I traveled there by foot, I
| would surely use a lot of energy as well. Not just food and
| breathing, but also cooking, heating of the BnB I am staying
| in.
|
| Surely you could say that this would be much less than a
| typing continental flight on a jet (you are probably right)
| and at that point the human CO2 can be considered a 0. But
| what exactly is that 0?
|
| If you assume human produces exactly 0 CO2 all relative
| comparisons become basically infinities. It's infinitely
| better to walk than to cycle, it's infinitely better to walk
| than to fly, etc. But it's not really true. It may be several
| orders of magnitude better, even - but how many exactly?
|
| I literally never saw this in the research in regards to CO2
| produced.
| Delphiza wrote:
| For all of the days that you are alive you need to eat,
| breath, cook and heat the room that you are living in. The
| continental flight just allows you to eat, breath, cook,
| and heat in different city. You cannot account for the
| carbon cost of the time that you spent travelling, as
| flying-self will still have a carbon cost sitting around a
| pool waiting for walking-self to arrive.
| lovemenot wrote:
| >> It may be several orders of magnitude better, even - but
| how many exactly?
|
| It's not an easy question to answer. I suspect it would be
| fun to try. Perhaps more for you than for me. But, aside
| from the pleasure of working this problem, there remains
| the other problem. And an answer to your question is almost
| entirely immaterial to that one.
|
| I think the difference between our approaches is that you
| are focused on relative amounts - how exactly to account?
| My concern is with absolutes: a metric fuck-tonne is coming
| from (effectively) nowhere and going into the atmosphere in
| almost zero time.
|
| It'll surely be more efficient to account for the future
| emission at the point of fossil extraction, with special
| consideration for reliable CCS.
| wyattpeak wrote:
| Honestly, I started working this out because I thought it would
| be negligible. But I think you're right to doubt. Leaving aside
| the question of how much a human produces, since two people
| have suggested human output is neutral and I don't know enough
| to question it:
|
| It takes an average of 0.10kcal to walk up/down a step,
| averaged.[1]
|
| 2.2kg of CO2 are emitted per 2000kcal of consumption (I just
| averaged table 3 for want of a better idea)[2]
|
| 37 steps in a staircase (TFA, 46 total - 9 flat)
|
| 3.7kcal burned, 3.7kcal * 1.1g/kcal ~= 4g CO2 per person per
| trip
|
| Obviously very rough, but unless I've made an order-of-
| magnitude error it's in the same ballpark.
|
| [1] https://pubmed.ncbi.nlm.nih.gov/9309638/
|
| [2]
| https://nutritionj.biomedcentral.com/articles/10.1186/s12937...
| NLips wrote:
| On the underground you're meant to stand on the right of
| escalators to leave room for those walking up on the left.
| However, TFL ran a trial a few years ago instructing people to
| stand on both sides during peak times. This actually increased
| overall throughout and per-person speed: throughput as you can
| more closely pack passengers standing rather than allowing a
| smaller number of walkers half the space (and those walkers are
| necessarily spaced out more than standers), and per-passenger
| speed because even though walking up the escalator would be
| faster, the increased throughout reduces the queue time at the
| escalator entrance, which has a greater effect.
|
| To my knowledge, they didn't move forwards with keeping the
| instruction permanent in peak times, presumably because it's
| difficult to implement / ingrain in people.
|
| EDIT: link https://www.shortlist.com/news/holborn-escalator-
| trial-tube-...
| zarzavat wrote:
| The way I understand it is that impeding someone trying to pass
| on an escalator in London (it doesn't have to be on the
| underground) is socially unacceptable. You can actually stand
| on whatever side you want, but you'd better be ready to get out
| the way if you decide to stand on the left.
|
| Making everybody stand makes people uncomfortable because it's
| essentially forcing them to inconvenience other people.
| alisonkisk wrote:
| simsla wrote:
| This is the way I remember it in Tokyo: stand on the side,
| unless it's super busy. Then you jam-pack as many people as
| humanly possible.
| fredley wrote:
| I took part in this trial, at Holborn Station. The escalators
| are very long, and few people walk. However, despite the
| signage, markings and announcements, when I stood on the left I
| still got the occasional tirade of abuse from someone
| attempting to walk up behind me! Most people continued to only
| stand on the right as a result.
| carschno wrote:
| I've been wondering about that story as well. My own conclusion
| is that the experiment failed because the metric of average
| speed per passenger is wrong from a passenger's perspective.
| People who stand probably don't care about a hardly noticeable
| increase in speed, whereas people who walk are annoyed by the
| very noticeable decrease in speed.
| NLips wrote:
| I think the speed _for all passengers_ was increased, because
| of the reduction in queueing.
| notahacker wrote:
| > This actually increased overall throughout and per-person
| speed:
|
| Increasing the average per person speed sounds like the
| expected result. Not necessarily a net win if the people
| sufficiently motivated to exit quickly to walk (who tend to
| bypass queues) are slowed though.
| frosted-flakes wrote:
| They still had the option of walking though. With two
| parallel escalators, 3 of the 4 "lanes" were for standing and
| one for walking, rather than reserving two lanes for walking
| when few people do so.
| gsnedders wrote:
| This was also only at Holborn, one of the typically most
| overcrowded stations on the network.
|
| A lot of the problem was that it was relatively unpopular, even
| with the increase in throughput. There was some talk about
| having at least one walking side per set of escalators, but
| that's also harder from a messaging point-of-view.
| koolba wrote:
| > On the underground you're meant to stand on the right of
| escalators to leave room for those walking up on the left.
|
| Don't they drive on the left in the UK? The "slow" lane should
| be on that end.
| rovek wrote:
| We drive on the left, which means we walk on the right (to
| see traffic coming), so I guess it stems from the latter
| YPPH wrote:
| In Australia, we drive on the left, but on escalators we
| pass on the right just as the parent comment envisioned.
| alisonkisk wrote:
| In the US, we walk at traffic when there are cars on the
| road but the passing lane is the same (left) for driving
| roads and for pedestrian multi-lane "roads" like
| escalators.
| yardstick wrote:
| Turns out it's just legacy from the original escalator
| design.
|
| "It all dates back to when the first successful escalator
| (there was a failed attempt to build a spiral escalator
| beforehand) was introduced on the tube in 1911 at Earl's
| Court Station. Alighting an escalator was different back then
| to nowadays. There was a diagonal partition -- beneath which
| the stairs disappeared -- that shunted passengers
| disembarking to the left. So it was decided that those
| walking up the escalator should stand on the left, otherwise
| they'd have to cut through a line of those standing. And that
| would've been mayhem."
|
| https://londonist.com/london/transport/why-don-t-we-stand-
| on...
| yardstick wrote:
| One thing I'm conscious of with these crowded escalators is the
| exit point safety, as some people can be rather slow to move
| away. Making both sides standing would make me concerned about
| seeing accidental pileups from people not moving away quickly
| enough.
|
| You get it sometimes already when the station itself is
| overcrowded- TfL normally starts limiting access, running
| congestion control etc. Fortunately most of busier places
| (Bank, Canary Wharf, etc) are full of regular workers who know
| the drill.
|
| It's more one off special events where causal travellers show
| up en masse.
| camjw wrote:
| The study shows this was better at peak times, especially for
| the goal of making sure there are no queues at the bottom of
| the escalators which can slow the tube down, but presumably in
| normal times (when there is space for standing and walking)
| this is worse for individuals who have a preference on walking
| or standing.
|
| I get the tube to and from Holborn every day and there are
| always people (me included) walking and I rarely arrive at peak
| times.
| MaxBorsch228 wrote:
| In Moscow metro they sometimes ask (but do not enforce) via
| speakers to stand on both sides of the escalator. I heard this
| practice was brought by McKinsey from London. In my experience
| this sometimes works on very short escalators, and on the
| longer ones people seem to ignore the suggestions. I wonder
| about the psychological reasons of this behavior.
| rkangel wrote:
| I've always thought of it as a classic latency vs throughput
| tradeoff. You sacrifice some individual latency (of the people
| on the left walking quickly) for improving the overall
| throughput of the system (and therefore worst case latency).
| wikfwikf wrote:
| Their justification for this change, as I read it back then,
| (the linked article doesn't get into the details) seemed to me
| to be completely flawed.
|
| It is true that standers are more closely spaced together than
| walkers. The number quoted was a stander every 2 steps versus a
| walker every 3 steps. However standers spend roughly twice as
| much time on the escalator as walkers do. This means that
| walkers take up about 50% more space*time on the escalator,
| which is the constrained resource.
|
| This error was exacerbated by station staff observing queue
| length as a goal to minimize. Walking on the left leads to a
| longer, and also faster-moving, queue for the left side of the
| escalator. People are happy to stand in this queue, because
| they are trying to optimize for the time they get off the
| escalator, not the time they get on. But station staff sees
| reducing this queue as a success. This is wrong - firstly they
| don't take into account the higher throughput for the left
| side. Secondly, making things less desirable definitely makes
| queues for them shorter, but this is not a win.
|
| In short, standing-only can reduce total travel time for
| congested escalators where few people walk (obviously), but it
| makes things quite a lot worse for busy escalators which are at
| capacity for both walking and standing. (Even before you
| account for the fact that walkers on average care more about
| their speed than standers.)
| rjmunro wrote:
| The trial was at a station with 2 parallel escalators going
| in the same direction, giving 4 lanes of people. Instead of
| having 2 standing lanes and 2 walking lanes, they had 3
| standing lanes and 1 walking lane. The goal was to reduce
| queuing for the standing lanes. The walking lanes are usually
| a lot less busy.
| wikfwikf wrote:
| When I travelled through Holborn during this period, they
| had changed both of the up escalators in the main bank
| (ticket hall down to Central/Piccadilly fork) to 'standing
| only'.
| pydry wrote:
| I got kind of mad at this decision for precisely the same
| reason as you.
|
| I'd like them to put up some signage to encourage people to
| walk up (it's a low friction way to get some exercise) and
| try again. I reckon they could increase throughput and make a
| few people slightly healthier this way.
| stdbrouw wrote:
| I lived in London for a year or two and I rarely saw an
| escalator "at capacity" for walking. You can do all of the
| napkin math you want, but ultimately, as the article says:
|
| > The one escalator at Holborn that allowed you to walk up
| the left side during the trial had a total of 115 passengers
| per minute, but the standing-only ones knocked that up to
| 151. This was only the case during peak times though - when
| you've got under 100 people on the escalators, it doesn't
| really make much difference. Either way, introducing
| standing-only escalators meant that they only had to SHUT THE
| GODDAMN GATES AAAHHH once during the trial, whereas it was
| happening almost daily before.
| wikfwikf wrote:
| I have seen lots of escalators at peak capacity for
| walking. Perhaps you didn't travel a lot in rush hour.
| People (for obvious reasons) are much more likely to walk
| up escalators in the morning rush hour than in the evening.
|
| The escalators at Holborn are somewhat exceptional as was
| noted in the linked article, and the anecdata provided by
| station staff is not particularly convincing. If the
| station was extremely congested in the morning, it is hard
| to imagine that very few people chose to walk straight onto
| the left side of an escalator rather than queue at length
| to stand on the right.
|
| 'Shutting the goddamn gates' really only happens at
| stations like Holborn in the evening when people are trying
| to get out of the city centre. The up escalators at Holborn
| are conversely at their most busy in the morning, so this
| is a confusing claim at best.
|
| As for the accusation of 'napkin math', I was simply
| responding to the clearly wrong napkin math which was
| widely cited in favor of this change. This purported to
| show that even at capacity, a walking left side was
| wasteful of escalator space. Without this flawed claim the
| main consideration simply becomes that if the left side is
| being used a lot for walkers it should be kept for walkers
| (obvious) and if not, not (also obvious).
| adammarples wrote:
| It doesn't really work like that, people are lazy and even at
| peak times will queue at the right hand side to stand, even
| when the left hand side is completely empty
| nicgrev103 wrote:
| 'Stand on the right' is relative to which way you are facing.
| You would still be correctly following the instruction if you
| are facing opposite to the direction of travel and standing in
| the way of 'walkers' (on your right). I find Londoners
| generally receive this sort of humour very poorly ;)
| a_c wrote:
| Just want to comment that, that's essentially public transit
| within a public transit. Public transit cares for throughput,
| private transport (cars, left-lane of escalator) cares for
| latency. Queuing theory in a nutshell.
| amelius wrote:
| Could the escalators going down generate the power for the
| escalators that are going up?
| KineticLensman wrote:
| All escalators go up AND down - it's the direction of the side
| that is on the top that you notice as a user.
|
| Also, they aren't powered by gravity but by motors.
| amelius wrote:
| That's irrelevant.
|
| The sign of the power needed/received for moving passengers
| up/down depends on the direction of the escalator as viewed
| by the user.
| danbruc wrote:
| If they were friction less, they would be in balance without
| passengers and would start moving downwards with passengers
| stepping onto them at the top. And could theoretically move a
| lighter group of passengers on another escalator upwards. In
| practice it seems very unlikely that one could make this work
| with reasonable effort. It already starts with the fact that
| you are probably not going to have well balanced streams of
| passengers in both directions most of the time.
| midasuni wrote:
| Over the course of a day across the system the number of
| passenger-kg going up will be roughly about the same as the
| number going down. More going up in the morning, more going
| down in the evening.
| ajsnigrutin wrote:
| But the escalators carrying the people "down" have the help
| of the gravity pulling all those people down and the motor
| works mostly as a brake...if the motors fails, it speeds up:
| https://www.reddit.com/r/WTF/comments/uegc45/escalator_break.
| ..
|
| So, if the motor worked as a generator too, it would only use
| power when turning the empty escalator (because of friction),
| but when enough people are standing on it, it could actually
| generate power.
| rjmunro wrote:
| Yes, escalators going down can generate power for the local
| grid when there are people on them. Modern escalators do this.
| E.g. https://www.kebamerica.com/blog/vfd-regen-escalators/
|
| It doesn't particularly power the escalator going up, it just
| reduces the power consumption of the whole building.
|
| There was also the Levytator where instead of the stairs
| looping underneath at the end, they go around and form the
| opposite escalator: https://www.youtube.com/watch?v=x58272OirGU
|
| This means that people travelling down automatically help
| people travelling up because they are on the same mechanically
| linked stairs.
| mzs wrote:
| Honestly this is more 'arithmetic of escalators' than
| mathematics. But now I'm curious, anyone run across some related
| math? Graph theory and combinatorics immediately come to mind.
| virtualritz wrote:
| This is what happens when you do not use something like LaTex to
| typeset a paper.
|
| The amount of typographical/layout crimes screaming in your face
| on the first page already made me not want to read this - however
| curious the topic.
| Reason077 wrote:
| There are some outdated assumptions about the carbon intensity of
| electricity being made here. They seem to be assuming coal-fired
| power emitting 0.9kg CO2/kWh.
|
| In reality, the actual average carbon intensity of the UK grid in
| 2021 was only 187g CO2/kWh: nearly 5 times less! So escalators,
| in the UK at least, aren't nearly as bad for the climate as this
| article suggests.
| lsllc wrote:
| TBH, I was astounded at just how much CO2 was being emitted
| according to TFA. So 5x less is way better -- I know the UK is
| doing a pretty good job on renewables, esp. wind [0].
|
| [0] https://www.theguardian.com/environment/2021/jan/28/uk-
| elect...
| t_mann wrote:
| This is urgently missing some discussion of queuing theory /
| stochastic processes. Discussing passenger flow in terms of time
| averages is misleading, passengers don't arrive in continuous
| streams. The peak load will be many times the average, which
| impacts power consumption, while at other times they will be
| running almost empty with just a handful of passengers.
| toolslive wrote:
| It's actually not that bad to assume a crowd is a fluid. For
| example it allows you to deduce where the hotspots will be when
| there's a panic.
| tomsto wrote:
| Disagree. Firstly there aren't many situations in fluid
| dynamics where there is a steady constraint on mass flow.
| Velocity just increases. (The exception is choked flow from a
| nozzle IIRC)
|
| Now think about what happens when 6000 people/hr leave the
| station but arrive on 12 trains over the course of the hour,
| i.e. in surges. Each peak demand will comfortably exceed the
| flow rate of escalator.
|
| You get a queue; the equivalent in fluid dynamics would be an
| increase in density upstream of a choked nozzle at Mach 1 but
| how to turn that into a relevant metric for eg queue length?
|
| Thats also the reason - I suspect - that in many Tube
| stations two escalators go up and only one goes down.
| toolslive wrote:
| Plenty of researchers went the fluid route. Also
| intuitively, it's viable. A simple example. If you want to
| step onto a train, the best place to position yourself is
| next to the doors of the train, not in front of them. The
| stream of people coming out of the train makes it so that
| the pressure is lowest where you stand. Anyway, there are
| plenty of papers on the topic.
|
| fe this paper: https://www.sciencedirect.com/science/articl
| e/abs/pii/004116...
| capnahab wrote:
| Fascinating and something to think about as I ride the Piccadilly
| line escalators with my mind in neutral. Thanks.
| eynsham wrote:
| Apropos, Peter Campbell on the maintenance of escalators in the
| _LRB_ : https://www.lrb.co.uk/the-paper/v24/n05/peter-
| campbell/why-d....
| llampx wrote:
| I hope they do an analysis on the escalators in the new BER
| airport.. maybe we could find out the stroke of genius that
| designed the airport with escalators that only go up. Emphasis on
| stroke.
| Chris2048 wrote:
| Shouldn't a down-hill escalator be able to generate electricity?
| dmurray wrote:
| Apparently frictional losses are too high.
|
| This seems intuitively believable: I'm imagining an escalator
| disconnected from its motor and wondering whether a constant
| flow of people (stepping on, but not walking downhill) could
| keep it running at 1m/sec.
| MrPatan wrote:
| What would be the minimum number of passengers it'd need before
| it can go by itself?.
| thombat wrote:
| Doing this in a non-spherical-cow environment will be
| challenging, because the gravitational load varies (passengers
| stepping on/off) but it's probably important to keep the
| velocity fairly constant to avoid upsetting the balance of
| those standing on it, let alone those walking down it. So it
| likely needs the generator load to be very responsive to the
| behavior of a long loop of rather heavy objects with quite a
| lot of friction, motor driven via reducing gears.
|
| Maybe instead of thinking of generation, it's more a question
| of regulating the applied motor power to keep constant
| velocity?
| lsllc wrote:
| That was my thought too, from a mechanical design point of
| view, perhaps some sort of funicular design perhaps where the
| weight of the passengers going down helps left the other side.
| But maybe some sort of regenerative braking on the down side
| charging batteries to assist the up side.
| jerome-jh wrote:
| It would certainly be possible to recover some of this energy.
| Just like it is possible to recover some of the heat lost by
| people: https://www.greenchipstocks.com/articles/body-heat-
| from-pass...
| Symbiote wrote:
| Why doesn't London Underground use either slowed or stopped
| escalators when there are no passengers?
|
| I noticed in Berlin, escalators without people often run very
| slowly. They speed up as soon as someone steps on.
|
| In Copenhagen, they stop. This is presumably more efficient, but
| it's easier to assume the escalator is broken, and a bit
| disorientating.
| everfrustrated wrote:
| Where new escalators have been put in they do. Mostly this is
| in new stations or station entrances. Eg the new Cannon St Stn
| entrance.
|
| I suspect there's no reasonable way to retrofit them to
| existing ones - probably requires a different type of electric
| motor and AC speed controller plus sensors which is getting to
| be a pretty big job (so expensive even if the parts aren't).
|
| It takes TFL about 9 months to replace out an old escalator for
| a new one. I think I'm correct to say they have 50 year
| operational lives.
| ajsnigrutin wrote:
| > It takes TFL about 9 months to replace out an old escalator
| for a new one. I think I'm correct to say they have 50 year
| operational lives.
|
| Seriously? Why? Genuinely curious
|
| It takes them a few days to replace the ones in local
| supermarkets, including the flat conveyor ones to carry the
| trolleys.
| brk wrote:
| From a few cases I have seen, it is partly due to the very
| long service life. New units are substantially different
| from older ones, particularly in all the bits of it that
| you do not see as a pedestrian. Often times the retrofit
| involves a lot of concrete work and other work to adapt the
| mounting and support points to accommodate the newer
| designs. Couple this with the fact that you are usually
| doing the work in sub-optimal conditions because they are
| trying to keep the rest of the area open for pedestrians,
| so there is additional safety considerations that you don't
| have in a new construction install.
| Delphiza wrote:
| The health and safety aspect is mind-numbingly overbearing.
| And for good reason. It is an underground workspace that is
| surrounded by the general public. When escalators are
| replaced the entire work area gets boxed in. There must be
| significant controls in terms of dust, gas (like welding
| equipment), noise etc. Fire is a significant risk and the
| underground has history that makes them anxious about fire
| and escalators (see Kings Cross Fire). Most of the work
| probably has to take place after hours, and subject to
| other maintenance taking place. On the underground, you
| can't just put a new escalator in a docker container and
| spin it up. The Underground is a significantly complex
| environment.
| Symbiote wrote:
| Probably because they're bespoke, subject to heavier use,
| located in confined spaces, and are expected to run 20
| hours a day for 50 years.
| lozenge wrote:
| I'm not sure any of them would turn off for longer than 2-3
| minutes at a time. The minimum frequency would be about 12 tph
| (5 mins interval) but that's in each direction. You only need
| one person alighting from a train to cause the elevator to turn
| on. The less used suburban stations don't have escalators at
| all.
| zarzavat wrote:
| Some of the escalators on the Underground are terrifyingly
| deep. They could do variable speed for some of the shorter
| ones, but implementing that for the long escalators would cause
| more than a few accidents.
| samhw wrote:
| Yeah, I'm not sure non-Londoners appreciate this. The
| escalators at Angel (where I grew up) go 60m deep. Someone
| skiied down them and hit 30mph: https://en.wikipedia.org/wiki
| /Angel_tube_station#Escalator_s...
| https://youtu.be/rlF4nRUbKmc?t=53.
| DoughnutHole wrote:
| This is something I noticed experiencing undergrounds in
| Germany after previously only experiencing them in London -
| London's escalators are insane, the Cologne U-Bahn is
| practically surface level by comparison.
|
| If I were to hazard a guess this is because of the soft
| clay that London is built on - on the one hand the soft
| material makes it very easy to dig tunnels, on the other
| hand if those tunnels are dug too shallow they will very
| easily destabilise the foundations of the buildings above.
| So you have to to build them at a depth which would be
| prohibitively expensive somewhere built on harder rock.
| andylynch wrote:
| Not only that, as Crossrail demonstrated one must also
| avoid the numerous existing tunnels (not just trains, but
| also utilities and even rivers). Not all of which are
| precisely mapped or even know about! Even then, the gap
| between tunnels in some stations is on the order of
| centimetres
| [deleted]
| wikfwikf wrote:
| Some tube lines are very deep but there are also several
| which are cut-and-cover, ie at the same just-below-street
| depth as the NY subway.
| dan-robertson wrote:
| I think part of the reason is just that they aren't frequently
| replaced (I think it is often a very annoying place to install
| new escalators).
|
| Personally I prefer to manually climb the stairs and I'm often
| surprised by how much space there is between escalators (it
| often seems like 50% of the width of a tunnel is just metal
| closing up the space between the parts of the escalators you
| can stand on) but I think my opinion is rare and it would be
| inefficient to have a flight of stairs that nearly nobody uses.
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