The hole just isn’t big enough.


In my last post about driverless trains (December 2013) I queried how much longer it would be that we were going to be stuck with 12ft diameter tube tunnels. The much-extended London deep tube network was a product of late Victorian thinking and while it was a brilliant solution at the time it struggles a bit today. One problem is that people have got bigger. Moreover the sclerotic  stations are less efficient not just because of crowding (far more people than that for which they were designed to operate efficiently), but because of changing passenger behaviours which means flows are slowing down.

The more I travel about when it is busy (and it is now busy most of the time), the more I am surprised that nobody seems very concerned and that there is no long term plan to deal with what I see will be a problem. I am not suggesting we begin wholesale reconstruction tomorrow, of course. But in a hundred years can we honestly expect any of these tiny tunnels to be in use in today’s form? I think not, for the reasons that follow, and that leads to the next question. When, between now and a hundred years hence, will something be done? There’s a lot of deep tube, about 280 single track kilometres, in fact. So whatever is done will need careful phasing over many years. That being the case, some kind of plan is surely needed, and we need the debate sooner rather than later.

Why the tunnels are becoming too small for purpose

My interest in making the tubes bigger was partly stimulated by observations from others that people are getting bigger. I observed that between 1875 and 1975 men aged 21 have on average increased in height from 5ft 5ins to 5ft 10ins and that the door height of a 1972 stock train is but 6ft 1ins. If we do the statistics, based on a spread of heights of those aged between 20 and 49 it means that in 1875 pretty much everyone would have passed through a notional 1972 stock doorway, whilst today 12½ per cent of males need to stoop whilst entering the cars and even then some of them cannot stand straight up without banging their head on the roof. At first it seemed apparent that in just a few years the proportion of passengers banging their heads would double, but then I realized that the latest 2009 tube stock has doorways that are a couple of inches higher (achieved in part by lowering the floors) and this is putting off the evil day when the average person is larger than the hole in the side of the train. Nevertheless, people are getting bigger and the tunnels are not.

There are also safety issues to consider. Today’s expectation for tube construction requires an escape walkway to be provided along one side of the train, whilst existing tubes (with odd exceptions) have no escape facility except at the ends of the trains. This is problem enough today, but ‘grandfather rights’ and experienced staff mitigate the obvious dangers. I cannot help thinking that as the decades roll by, the safety authorities will become increasingly intolerant to the lack of additional means of escape, especially if LU pursues the ‘driverless train’ concept, in whatever form it develops. This at least invites consideration about enlarging tunnels, and if that were to be the plan then enlarging to main line size should surely be looked into.

As a guide, the existing tubes are about 3.6m in diameter, the Jubilee Line tunnels with walkway are about 4.35m, itself considered a compromise – ideally it would have been bigger to reduce evacuation times. Crossrail tunnels have an internal diameter of 6.2m and allow for main line stock with overhead line equipment. Perhaps if the 4-rail system is to be perpetuated (itself an interesting question) then tunnels 6m in diameter would do.

To give a flavour of the effort required, enlargement would require removing almost twice as much spoil per unit length of tunnel as driving the original tunnels required. We then have the issue of whether enlarged tunnels would clear existing nearby structures and tunnels, and all which that entails. In short, this depressingly vast task is not something to embark upon lightly and my concerns are based entirely on the premise that one day, however far away that might be, the existing small-bore tubes will simply not do the job.

The recent Central Line strike, and the little motor difficulty they had a few years back when the line closed entirely for weeks, made me wonder whether that line would be a good candidate for early reconstruction. I offer the following thoughts:

  1. Virtually all the open air parts of the Central were built to main line gauge and the alterations required to restore such a gauge are (in the great scheme of things) quite small.
  2. It appears that London can function without the Central Line for extended periods at present traffic levels provided reasonable alternatives are provided.
  3. Much of the Central Area of the Central Line is duplicated by or accessible from Crossrail, at least partially. Once Crossrail is opened, but before its traffic has fully developed, there appears to be a once-in-a-lifetime window of opportunity to close the Central Line for reconstruction. (To divert Central Line trains into Crossrail tunnels before Crossrail services start would have been a realistic option for allowing Central Line reconstruction; alas, not now possible. Crossrail 2 might have offered a second opportunity if it were to take over a Central Line branch, but this is no longer the current plan).
  4. The Central Line will be one of the lines needing new rolling stock anyway within the next decade or so, probably with entirely new signalling, so the timing is reasonably good.

Although the Central Line is mainly straight, there are a few extraordinarily sharp bends in it and these could be eliminated, with consequential speed improvements (some other lines might benefit even more from elimination of irksome curve-related speed restrictions)

As already indicated, reconstruction of any tube line would be a formidable challenge, even though it has been done before and some of the issues are well known. It is probably not feasible to attempt enlargement with trains running (as was done previously) so closure for probably at least two years seems unavoidable. But what of the stations? If one is increasing the comfort and capacity of the tunnels then major station works are also invited, and may be necessary anyway, for example where platform access subways cross tracks at tube heights. Longer platforms perhaps beckon?

It may be argued that it would be easier to build new tubes and just abandon the old ones that could perhaps make useful cable or air ducts or emergency escape routes. The problem is that it is very difficult to find new routes across London at sensible depths, while the existing tunnels self-maintain their ‘right of way’ between the invading deep foundations of London’s vast new buildings.

And People are moving more slowly

On the subject of stations, I fear that here, too, some kind of step change will be required sooner or later. Many Underground stations (and not just in Zone 1) are already at bursting point and any delays create a real problem for the staff. I sometimes watch with astonishment at the way seemingly impossible crowds are dealt with daily at some very poorly designed stations (and I say this as someone who once managed Victoria!). Without a long term plan I fear possible crisis where a large number of stations will require massive congestion relief schemes all at once. If a whole line is to be reconstructed then obviously this aspect needs coordinating too; it might even make the job easier.

I have been looking at some LU standards relating to handling passenger flows and I wonder whether these remain fit for purpose in the light of my own observations about passenger behaviours. For example, I am not at all sure that the standards for handling traffic in passageways and other public areas match what is now happening. I have been doing my own studies recently and make four observations.

  1. In very rough terms about a third of people in any crowd (including a moving crowd) are using some kind of mobile device, be it a mobile phone or music device (often combined) or a reading device. In the majority of instances the owner is fiddling with it, and it is to the device that immediate attention is focused.
  2. In virtually all cases where a moving person is fiddling with an electronic device whilst moving, their speed drops to about half that of the ‘ordinary’ flow, thereby causing the whole flow to slow down in relatively crowded or narrow spaces. (I invite you to check this for yourself.)
  3. In addition to slowing down, navigation virtually ceases and users are apt to weave across spaces (causing further slowing of flows) and then suddenly correct as peripheral vision identifies ‘obstructions’, such as a person coming the other way.
  4. When something exciting is happening on their electronic device, some users will just stop dead where they are, causing havoc to the flow rate. This includes trying to finish off a phone call inside a station entrance before the signal fails farther in, a particularly difficult track change between pieces of music, maybe requiring both hands, or the end of a very exciting chapter on their Kindle.

Let us be clear, if this kind of behaviour were isolated (such as those reading newspapers whilst going down stairs in a busy rush hour) then we just shrug it off. My own observations (St Johns footbridge at Clapham Junction is an excellent place to do this) suggest it is a massive and growing problem and that it is beginning to interfere with flows through stations quite seriously. Go and see for yourself; I recommend those mean not-quite-wide-enough subways of the 1960s/70s to be a good place to start. I do not have an answer to what I see as a mounting problem, but do think it is a factor that may not have received due attention by planners and is getting worse.

Luggage and baggage

In much the same vein I feel moved to mention the issue of luggage. When I first began using the tube in rush hours, it is my feeling that the majority of passengers did not have ‘luggage’ in the ordinary sense of the word. Many men carried nothing or a folded newspaper and umbrella, with a proportion having a modest sized briefcase. Women generally had just a modest-sized handbag with perhaps a shopping bag into which the handag was placed. In the evening, notably on Thursdays, carrier bags containing shopping items might be carried (anyone else remember the enhanced Central Line services on Thursday evenings to cater for ‘late night’ shopping, when ‘late’ meant 8pm?). True ‘luggage’ was not altogether uncommon but there was comparatively little of it, particularly in the rush hours when no-one who had given the matter any thought would bring suitcases.

Well, it isn’t like that now.

Luggage is today carried in vast quantities, and not just on Heathrow trains where the grudging accommodation struggles to cope. Nor is it simply the quantity of luggage, it is the size of it and also the amount of it in relation to the people carrying it. Some luggage is so vast that it needs two people to carry it, with consequential impacts on boarding times and safety, for example on escalators, where it totters precariously and no-one can pass.. Moreover, I often see people with far more luggage than they can move alone, so bits of it are left whilst the rest is moved, to the consternation of station staff looking at what (to them) is a large suspect package. It is touching that people think it will still be there when they return! It may be my imagination, but quantities and weights of luggage seem to be going up, and this is not good for the operation of an already too busy and too small station.

I also need to mention the back-pack. Another recent survey of mine (Baker Street provides a good vantage point) suggested that very nearly half of the people I watched using an escalator for twenty minutes either wore a back pack or a large shoulder bag slung in such a way that it was effectively a pack pack, or had other large luggage with them. I will avoid wasting more than nominal space wondering why quite so many people need to be carrying items with them apparently sufficient to sustain them for a long weekend up a mountain, for the point is that they now do whilst once they did not. Now, our old friend the escalator had its material dimensions set in the days when small briefcases were the norm, and now they are not the norm. A briefcase or handbag held tightly at the side causes virtually no additional impediment to flow than its carrier would if travelling alone. This, in crowded conditions with an escalator operating at 145 ft/min (once its optimal speed) allowed the majority of treads to be occupied, or, at least, their right hand sides.

A back-pack, or its equivalent, unfortunately sticks out materially to the rear of its carrier and will often make it impractical to occupy the next step (occasionally next two steps), at least if one doesn’t want a face full of back pack from a fidgety wearer oblivious of anything behind. I would not go so far as to say my study is sufficiently rigorous to redesign our station standards, but it is apparent that, on the face of it, escalator capacity is being materially reduced by this change of fashion, coupled with the luggage problem already alluded to. Again, the odd pack pack is hardly an issue but when it is apparel worn by over a third of passengers it begins to take its toll. I will forbear from other observations about this handy piece of kit, but the number of times these things get caught in train doors, or strike other passengers whilst their owners swivel about oblivious, is perhaps worthy of separate study but again wearers do not always seem conscious that the appendage sticks out to the rear a long way from their own centre of consciousness. My guess, for discussion purposes, is that escalator capacity may be reduced by about ten per cent by this change of fashion, and this is, I suggest material.


From this, I think I may summarize what I believe to be two strands of thought.

The first is that with people getting bigger, and walking slower whilst distracted, and carrying things that are larger and heavier, any tendency of stations to reach full capacity will be accelerated. If we think we might have a capacity problem, I think it could be worse. The second is that I am not sure that existing capacity standards (or for that matter operating procedures) are picking this up and perhaps more research needs to be done on how real people actually behave and whether the answer is to change standards or try and change behaviours.

Personally I find it selfish beyond belief that people immerse themselves in a little world of their own when using electronic busy places – almost as though the rest of the world ceases to exist. The truth is, I suspect, they don’t give it a moment’s thought. Apart from inviting us to mine more underground space in stations, at vast cost, the magnetic draw of electronic devices not only slows everyone down but creates material hazards. A recent project I was involved with discovered that significant numbers of people in the street were colliding with trams. They were not being hit by the trams, they were walking straight into the side of them. The suspicion was that their attention was entirely directed to their electronic device and, expecting the pedestrianized street to be clear just walk straight into the vehicle (research indicated the same phenomenon in several large European cities). We see some comparable evidence for accidents or near misses at foot way crossings over railways where electronic distractions are implicated. It would be a surprise if London Underground was in any way immune from accidents caused by this kind of distraction, but I can see no easy solution.

Returning to my theme before closing, the Underground is simply not big enough for the passenger demand now, and this is aggravated by passenger behaviours that may be impractical to change. One factor (but only one) is the size of the deep level tube lines, a legacy from Victorian times, for that is when the legislation was passed that created the core system that effectively defined the size of any further extensions. That deep-level system has served us well for a century, but I seriously question that it can do so for another hundred years, given all the prevailing pressures. Making any change will be horrendously difficult and costly, but will, I contend, have to be faced. It seems to me better that we start thinking about this now so an organized response can be considered and phased in over perhaps the next fifty years (it needs to co-ordinate with train renewal plans). It is a problem that will get worse, and not easier, the longer that it is left. However, major reconstruction does open up other opportunities that might not otherwise be considered, for example the scale and timing of station reconstructions, and even perhaps how our outer branches (and which outer branches) link to which central London deep level core lines.

I think we need the debate about the very long term future of the small bore tubes, and the time to start it is now. Perhaps at the very least, we should be insisting on passive provision being made in that any new tunnelling should contemplate eventual use of larger trains (I doubt in the planners of the Battersea extension or Bank reconstruction have this in mind). But our transport planning system is dominated by the mayor of the moment and other politicians who have little inclination to take very long term views and an electoral system that doesn’t exactly reward very long term vision, especially if it costs now. Having said that, I do think Londoners would have little problem connecting with the idea that the old tubes and many of the stations are apparently far too small. We need today’s practitioners and users to start any debate, so why not here and now?

By the way, on the last four out of five occasions I used London Bridge and the two flights of escalators in the exit routes, not one person was walking either up or down for the whole duration of my exit. It was so extraordinary I even photographed it: left hand side of all escalators clear.  What’s going on? Is this another capacity-reducing tendency running amok? Keep your eyes open and keep asking the questions! 

About machorne

I have always lived in London and taken a great interest in its history and ongoing development. This extended into the history of its transport services, about which I have written a number of books - I have spent most of my working life working in the industry and observing changes from within, mostly to the good, but not always so. I continue to write, and have a website with half finished stuff in it so that it is at least available, if not complete. Several new books are in hand. I have many 'works in progress' and some of these can be found on my website; the we address is
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5 Responses to The hole just isn’t big enough.

  1. Taz says:

    The cost of expanding tunnels will dwarf the cost of modifying surface lines, so the Central Line is the best place to start with only around a third beneath the ground, similar to the Piccadilly Line. Then come the Bakerloo & Jubilee at around half, and the Northern near two-thirds!


  2. CyberGreg says:

    Even the relatively new Victoria line has got very tight walkways and platforms. It's only the most recent Jubilee extension that has got decent size areas.


  3. Anonymous says:

    Mike, you have well and truly hit several nails perfectly on their heads, and have pretty much word-for-word described my feelings over the past few years (as an extremely frustrated 6ft 1in eastern Central Line Zone 4->1->4 user).

    One suggestion/idea I had was to “square” the underground/deep tunnels so that we could alleviate the problem (you described) of the curve – this really restricts numbers of passengers getting on during the 7.45-8.30am crush, mainly because people don't want to crouch underneath the doors and therefore there is dead space between them and the mid/bottom of the doors.

    Another benefit of creating full-size/main-line tunnels would be the ability to share/upgrade rolling stock – the current stock is terrible, particularly amongst the “ride” which feels to me like the bogies are at fault, causing the excessive (and probably illegal) side-to-side jerking/juddering. More “solid” bogies would really increase the ride quality/comfort.

    Moreover, with CR2 not getting anywhere near East London/Essex now, and Central Line actually unusable in peak times, I wholeheartedly agree with the Central Line 1st approach.

    Finally, luggage – again, YES! I'd go so far as to punt a guess that restricting (or preferably banning) all baggage in peak hours would double capacity.

    One other matter which I don't think you covered – the seemingly god-given right to read (free) newspapers to the detriment and inconvenience of other passengers – ultimately in particular those who can't get on the trains because of the idiots who are taking up a further two people's standing space by reading some garbage – it almost feels like these people are powerless to free will and are BOUND to HAVING to read a newspaper just because they are on public transport/tube.

    An excellent piece – please share/distribute as far as you can.


  4. Pingback: Update on ‘unstaffed’ train operation | machorne

  5. Pingback: The phoenix and the constitution | Public Strategist

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