Small trains and small stations are good until they aren't, and then you're screwed.
Singapore built the orbital Circle MRT line exactly as the author wants: small trains (3 carriages, vs 6-8 on other line), small stations to fit these trains, frequent fully automated operation.
However, the line turned out to be much more popular than planners anticipated, with the result that at rush hour, it's common to have to queue just to enter the platform where you need to wait for multiple trains to arrive before you can squeeze in.
And the tricky bit is that there is essentially nothing you can do now to fix it. There's a hard physical limit (around 90 secs) on how fast the cycle of a train arriving, people getting on and off, and departing can get, and retrofitting all 30+ deep underground stations to be larger would be an insanely expensive and disruptive exercise.
That's true, but if you've kept a lid on construction costs as light metros tend to do, the public will embrace building new relief lines that bring more service to areas with moderate access. That adds big capacity you can then continue to grow into. Paris is a great example of this, they often just add whole new lines rather than trying to wring a bit more capacity from existing ones.
You can build another line. This one was cheap and the demand is clearly there. And two medium capacity lines are generally better than one high capacity line in terms of offering more options to travelers.
It is much more expensive to build another line at that point due to the increase in density of the city (and sometimes new requirements of stations to meet building codes). Nearly every high volume transit system out there has choke points that are extremely expensive or impossible to fix by building another line. The tunnel between VA and DC on WMATA’s Orange, Silver, and Blue lines is a 20 year project. Tracks for LIRR to go to Grand Central took 60 years from proposal to opening. It is viewed as nearly impossible to build a line parallel to the MBTA underground green line, a system that has short two car trains and 4 branches above ground on the Boston side, so very easily could use a parallel line.
Singapore started building MRTs in 1982 and essentially never stopped. However "just build another line" is a bit glib when you're dealing with a city state of 6 million people on an island roughly 40km x 20km. There is a huge opportunity cost if land is misused or underused.
Singapore's MRT lines are some of the most expensive public transport projects ever. The Circle Line, fully automated and fully underground, cost S$10 billion[1]. The recent Thomson-East Coast Line, still partially under construction, is projected to cost S$25 billion[2]. It was not 'cheap' by any means.
> You can build another line
Singapore is building another line: the Cross-Island Line[3]. It has planned or is constructing at least three more lines[4][5] to achieve something like 460 km by 2040, thereby exceeding the length of the London Underground. About S$100 billion is earmarked for public transport expansion.
But the Circle Line was, as someone who has used it ever since it opened in 2009, ill-conceived as a 'small line'. It is heavily overcrowded. Because of the immense traffic and somewhat lacklustre maintenance, it has suffered several delays and breakdowns. The ideal thing for LTA to do would be to expand each station's capacity, because it links all of Singapore's radial lines at heartland residential areas.
A similar thing happened with SkyTrain's Canada Line, where it reached capacity very soon after it was built. They did plan a contingency to be able to extend the platforms for somewhat longer trains, however.
Canada Line is a bit weird since it wasn't built by Translink and doesn't use the same technology as the rest of SkyTrain. It was under built by the P3 out of caution for opening in time for the Olympics and extreme cost control, but they were really pessimistic in ridership projections. It was always going to burst at the seams pretty quickly, especially with all the transit oriented development along the route. It should have been built to the same ~80m platform as the rest of SkyTrain.
My ideal default rapid transit buildout for midsized urban areas would basically be SkyTrain with value engineering to extend the platforms to 100 or 120m with minimal cost in the future.
> and retrofitting all 30+ deep underground stations to be larger would be an insanely expensive and disruptive exercise.
But before this you had no idea that there was so much demand, right?
It's quite a lot easier to sell a huge monetary upgrade on something oversubscribed rather than a huge monetary outlay that may be a complete white elephant.
It's an order of magnitude easier and cheaper to dig out a 6-car platform the first time around than to expand from 3 to 6 when the system is already operational. And it's a one-off price too: if the platform is built but not used, it incurs essentially no operating costs to have it sit there waiting for the day it's needed.
But that’s not what history shows us. The subway with the second most ridership in the US is WMATA. How did they get there? By going big with their plans in the 1960s. All the systems that thought small in that era (MARTA, BART, LA Metro) have much lower ridership to this day.
There is a good basis to this. Every new mile and station you add to a system compounds on the size of the system. The 11th station connects you to 10 places. The 51st station connects you to 50 places. Build small and you never get the critical mass needed to see widespread adoption.
The worst thing is the small line creates induced demand for that route. As in, people will literally move house and get jobs etc that are dependent on the route. So after they build it, the societal cost of "pausing for upgrades" is massive.
probably safety issues are a factor, it would be hard to get every one off if something happened at a station. But also it probably wouldn't get you much benefit over having two trains. The main advantage would be the back half would theoretically be able to load unload a little faster then if it was a second train waiting to come into the station, but with the downside that now the front half of the train needs to wait for the back half to unload and load before it can go on it's way
The replies to this comment remind me that the supposed unavoidable law of induced demand evaporates pretty quickly amongst urbanists when talking about things they want to build. At the risk of sounding really snarky, “just one more line bro”.
> if we run a system for smaller trains, we can build smaller stations for these trains, saving a huge amount on station costs. This costs us in reduced total capacity, but this can easily be made up for by increasing train frequency.
There is a safe minimal distance between trains, in fact, a safe distance for a given speed. Shorter trains are not exempt from obeying it. You can make shorter trains more frequent at the expense of lowering traveling speed.
What is the cap of throughput is due to these speed limitations is an exercise left for the author of the article.
For capacity calculations, headway is what matters. E.g. trains spaced 2 mins apart means that 30 trains run in an hour.
It’s the same with cars. A 2s headway with cars holding 1 person each means that the maximum capacity of a highway lane is 1,800 people per hour, no matter how fast they go (the cars are further apart at higher speeds).
Freeway capacity is maximized around 35 MPH. Faster, and the greater distance between cars reduces capacity. Slower, and there are not enough cars per minute per lane. So the goal of ramp metering signals is to throttle input to keep the freeway speed around 35 MPH.
> What is the cap of throughput is due to these speed limitations is an exercise left for the author of the article.
They already did that exercise:
> 3-car trains running at 30-40 trains per hour (a normal peak frequency for automated or even some human-driven metro lines) reach a capacity of about 18,000 passengers per hour per direction, well above the expected demand of any American line that doesn’t go through Manhattan.
40 trains per hour is in fact not "normal", but extremely difficult. Only a few systems in the entire world operate more than 30 per hour.
The fundamental constraint is not technology, but people and physics: you need to decelerate and stop, let people disembark and get on, accelerate and clear the platform. This cycle requires a bare minimum of 90 seconds, although IIRC a few lines in a few places like Paris and Moscow do 85 secs.
Yes, they are assuming a best-case scenario. Driverless systems are very expensive for reasons that have little to do with the cost of the driverless trains, if you're not going to consider those variables this kind of armchair speculation is a waste of everyone's time.
I don’t think anybody has tapped into the forbidden magic trick of having CBTC broadcast position and velocity instead of position alone. For vehicle ACC at least, there is a safe region of velocity and follow distance where a following train can plan to enter the space where the lead train currently occupies.
I wonder if it's possible to run trains at higher speeds closer to each other using fixed brakes embedded near the tracks, similarly to how roller coasters often have mid-course brake runs that are only activated in emergencies when the train ahead unexpectedly slows or stops.
We're at the point where we could easily fit so large a fraction of the rail length covered/overshadowed by the train with https://en.wikipedia.org/wiki/Track_brake that we could pull around 4 G deceleration if we cover the bottom in that brake chains (chain strong; chain flexy enough to just wiggle over humps in the track).
> Wait times are the second-most underrated component in making metro systems effectively faster (right after street to platform time).
Street to platform time made using public transit annoying in several Asian capitals. Wait times are the main reason why I often hate traveling with public transit even in a city with one of the best public transit systems - if you aren't planning your life around the transit schedule, the wait time is essentially an unpredictable part of your travel time (and if you do plan around it, it's one more annoying thing to deal with).
If you leave your doctor's office, and you have a 10 minute train home that goes every 30 minutes, then you really have a 10-40 minute train home - so for practical purposes, you essentially have a 40 minute train. Once unreliability or delays become frequent enough to start being a factor to consider, this could easily turn it into a 70 minute train.
Another big factor is the time between the actual start/end of the trip and the nearest station. Even with near-zero street-to-platform time (e.g. busses/trams) and reliable, reasonably frequent public transit, once you add it all up, a bicycle often ends up being faster than even excellent public transit.
Munich is a counter example: It has many lines passing through (almost) 11 stations. They run at maximum speed of 40 trains per hour. It is a traditional block signal system with each block being shorter than a train - so they can run trains packed into tighter space. Each train opens left and right doors simultaneously so people can board and exit at the same time.
Boarding still takes time. It is overcrowded at rushhour and brakes down regularily (a train being at a station for too long blocks all proceeding trains).
And at Oktoberfest time, the stations are soo crowded that boarding takes longer.
Munich is planning on building a second subway route. It just does not have the money nor the space to build one. There has been discussion on building a second tunnel below the first, or on enabling the common train system for overflow by suburban trains -- by installing more signals to run more tightly packed.
The second route is currently being built in Munich [0], with work started in 2017. I recently watched a youtube video by The B1M about rail projects in Germany that included a long section about the currently ongoing works in Munich [1] that gives a good visual overview.
Something I've been thinking about lately is short trains but long platforms. Basically, you split the length of the trains in half and then split the platform into two boarding areas. In this way trains can be scheduled even closer together than the the 3-min physical limit of of signalling because the one coming in behind doesn't need to wait for the one ahead to leave the station first. Its therefore possible to schedule several different services on the same two-track system such that they all skip a large fraction of stops (and thus run faster), but every station is still reachable from every other without transferring.
A simple example would be 3 services on the same line that follow a repeating pattern every 3 stations. ==[A]==[B]==[C]==[A]==[B]==[C]==. The service (AB) stops on the stations labelled [A] and [B] (skipping C). The service (AC) stops on the stations labelled [A] and [C] (skipping B). The service labelled (BC) stops on the stations labelled [B] and [C] (skipping A). In this manner, all three services skip over 33% of the stops on the line, but no matter what your origin and destination, it is always possible to travel from an [A] station to a [B] or [C] station (or another [A] station), and likewise from a [B] or [C] station.
To the extent I've worked out the logistics of this, if you allow for trains to catch up but not pass each other at the platforms, you can push this idea as far as only stopping at 2-in-5 stations without sacrificing headways or capacity.
Just a weird thing thats been taking my attention lately.
In a lot of train systems this exists in the form of fast / stop trains, the fast trains only do the bigger train stations, the stop trains stop at every station, servicing smaller stops.
As for short trains on long platforms, this is pretty common in NL where the bigger train stations can support both very long international trains and shorter local trains on the same platform; a train can switch to a center track halfway on the platform.
I don't think it would really work for a subway system; people expect it to be hop on, hop off. In some places the stops (or people's final destinations) are so close together they can choose to get on/off earlier/later, but this system makes that less viable. You'd have more people shuffling through train stations trying to figure out which train to get or whether they need to wait for the next one, also putting extra load on staff for confused not-locals. And finally, you'd need extra rails or tunnels so that a train can pass another.
It can work on a subway system because there are skip-stop service patterns on J/Z line in New York.
In terms of needing extra track, that's the brilliant part of it. Even though the different services all make different stops in my proposal, so long as they depart in a certain order they will never need to pass each other.
In the 2-in-3 stops example I gave, suppose that at the present moment there's an (AB) train at station [A], a (BC) train at station [B], and a (AC) train at station [C].
If they all depart at the same time then (AB) goes one stop to the next [B] at the same time as (BC) goes one stop to the next [C] and (AC) goes one stop to the next [A].
Then they should all depart again at roughly the same time (since they all presumably took the same amount of time to go one stop).
So (AB) goes two stops from [B] to the next [A] station at the same time as (BC) goes two stops from [C] to the next [B] station and (AC) goes two stops from [A] to the next [C] station.
Then the cycle repeats.
All three service run at the same time without ever catching up or passing each other.
If you use my two-boarding-area trick then the constraint can be loosened to allow different services to catch up (but not pass) each other, which then makes it possible to run 2-in-5 stops without adding a passing track.
To elaborate a bit, on the face of it the 2-in-5 system has 10 different services running on the line at the same time, because there's 10 possible unique combinations of 2 out of 5 things.
However, just like in the 2-in-3 example, many of these services can be run at the same time without passing or catching up because they are scheduled to move and stop in the same pattern (just offset from a different starting station.
Every single train in the 2-in-5 system can be categorized as either moving 1 stop then 4 stops, or moving 2 stops then 3 stops. Two services in the same category never catch up or pass each other. If you have two subsequent services in a different category then they simply take turns catching up and falling back behind (but ultimately never passing each other).
Here's a (rough) line diagram I calculated showing where each train is at every 3-min interval in the 2-in-5 system. Notice how they meet but never pass.
In terms of confusing people and knowing which train to get on, this is what I've come up with as a signage convention. All that's necessary to know what train to get on is the symbol on the map of your destination. If a train has the same symbol on it then it goes there.
I feel as if the time spent by each passenger walking to the right boarding area could easily surpass the dwell time of an extra stop or two.
Consider a metro system with trains 70 m long. With 10 m of space between the two boarding areas, that means the length between both sides of the station is 150 m. If the entrance to the platform is in the center, the walk to the middle of each boarding area is 45 m, taking about 30 seconds. If the entrance is at the end, that becomes 35 m or 115 m (taking about 20 to 90 seconds to walk). I think those figures are comparable to the dwell time of a typical metro system.
I do think it's a very interesting idea though! I think it'd work better for longer trains over longer distances, where the time spent accelerating and braking is often greater, but unfortunately few places are even considering anything shorter than 15 minute headways for such rail services.
Admittedly my calculations did not take walking-on-platform time into account, but what I have been assuming (based on figures I've looked up) is that each stop adds about 60 seconds to the journey time (30 seconds for dwell + 15 on either end for getting up to / down from cruise speed). I've also been assuming that the inter-station no-slowing-down time is 2 min.
So in a 2-of-5 stopping pattern you'd save 3 min every 5 stops, but depending on when arrive at the station you will sometimes get unlucky and just miss your train, in which case you'll have to wait an additional interval than you normally would for the next one (costing you 3 min). So for very short trips (under 3 stops) it actually makes travel time a bit worse since there's very few stops you can skip over in such cases. But for more median trips there is a saving, and for the longer trips it saves well into 2-digit minutes.
In your example I think in the case with the entrance at the middle of the platform there wouldn't be any real effect, because splitting the platform also in the middle doesn't marginally change how quickly you can get to the nearest open door on the train you want. There's no real need to get to the center of either boarding area. In the case of platform at the end of the station, I can accept that adds about 40 m of walking distance that wasn't there before (at least for some people), and that translates into an extra 20ish seconds. Less than that if you do the rational thing of walking briskly when you see you're about to miss your train.
So you're right that the platform split adds some time which isn't completely negligible, and depending on what fraction of the next n stops you want to skip it comes at a penalty of longer wait times for the correct train, but both of these are fixed upfront costs whereas the dividend accrues linearly the longer your on the train.
This is how it already works in Europe (at least in Austria and Germany, but I assume elsewhere in Europe as well).
You will also find long trains that split in half mid-journey, so you need to make sure you get in the right car or you'll go to the wrong place.
Edit: I guess it's not exactly what you're saying, in Europe you will find platforms split into several sections with multiple trains to board, but they'll be for different lines with different destinations.
How would that help? 3 minutes is the minimum separation distance, if the trains have different stopping patterns then that just means they'll be further apart for part of their journey. If you have to stay 3 minutes behind the train in front, you might as well stop at all the same stations that it does, you can only save time if you were further behind to start with, so you can't increase throughput by skipping stops.
Simplifying a bit, its because the train behind can be scheduled 3 min after the train ahead has pulled in rather than 3 min after the train ahead pulled out. Put another way, the safe stopping distance to maintain (while at speed) would be measured from the half way point of the platform rather than the start of the platform.
This lets you schedule them much closer together than the conventional 3 min while still being safe.
I feel like this is one of those articles that claims some clever idea on paper but without experience of how this would actually work IRL but IDK if the OP has more experience than me so I will assume the best.
Others have already pointed out some of the practical things that would limit what you can achieve with shorter trains like minimum headway between trains and the congestion that would occur after a delay where you would expect people to wait for maybe 10 short trains to arrive and depart before you could get on.
There are other problems. The cost of the smaller trains means if e.g. 2 carriages each, then every other car is a driving vehicle with motors and control equipment. On longer trains, this could be 1 in 3 or 1 in 4. Each of these not only requires regular maintenance (so that's doubled the maintenance requirements) but also creates massive congestion issues in maintenance yards. Commonly, 1 or 2 full trains fit in each siding so getting most trains out if e.g. one is broken down is usually easy enough. Imagine having to move 3 or 4 separate smaller trains out of the way, they are not automated in the yards.
Most people would be very unhappy knowing that they might be alone on a train, which is a main reason why operators are not quick to get rid of all staff. But currently, a single driver and conductor is close by for, maybe, 8 carriages. This would double if you needed a single attendent on each 2 carriage train.
The signalling is very heavily designed around traditional trains with its delay after passing a signal. 4 x 2 carriage trains would utilise more signalling capacity/time than 1 x 8 carriage train. If these were all coming from the same location and needed to return, that would also need a lot more platforms so that the following trains don't block the first trains in terminal platforms. This is already a major problem at most UK terminal stations so that is largely unsurmoutable.
I also heavily question the idea that station cost is largely dependent on platform length. On most surface stations, platforms are relatively easy to construct and whether they are 4 carriages or 12 carriages long still require a station building or 2, some ticket machines and CCTV etc. For elevated railways that is more likely to be true maybe.
So yeah, like someone else said, we are unlikely to come up with ideas that 1000 other engineers haven't already asked, the easier problems to solve are around planning, design, legal rights for infrastructure projects etc. since these tend to eat up sometimes decades and billions of dollars.
The author spends a lot of words talking about short trains and Jersey City, but didn't once mention the Hudson Bergen Light Rail which was at least built in recent memory? I mean other than driverless operation it seems to check all the boxes. And in that light, I really fail to see the novelty in this argument; it's basically the multi-decade-old argument that building light rails is cheaper and better than real metro or heavy rail.
there is nothing new about trains - we need to stop looking for innovation and just build them with small incremental improvements. The only useful innovation since 1920 is full automation (though I'm going to call high speed rail incremental since it is mostly a lot of small improvements on the way - this is debatable). Even full automation was a lot of incremental improvements.
That said, full automation is a major game changer because it enables short trains with high frequency which you would otherwise struggle to afford. Don't build light rail, build light metro which is a small cost more (build a metro with light rail) but now you can have full automation.
I also thought this omission was conspicuous. The author has some reasonable points, but the sections on NYC and NJ felt like political wish (spite?) casting: just about the only state in the US that struggles more to build mass transit than NY is NJ. The HBLR is a rare survivor in an otherwise very crowded graveyard of NJ mass transit projects.
I don't think there is any danger to running more frequent longer trains. Ultimately you are constrained by the signalling system; nobody is suggesting "just disable the tripcocks and plow through red signals". Modern systems use moving block cab signals, so are set up to succeed with high frequency. (But there are other problems, like terminal capacity, that can limit frequency. The MTA in NYC spent a ton of money giving the L CBTC to run 40+ tph... but the terminal at 8th Ave can't turn that many trains. Until that's fixed, the L will always be overcrowded.)
You can see whether the problem is being cheap or if it's actually a capacity issue. If weekend service sucks but peak hour service is good, then it's just being cheap. If rush hour can't handle passenger volumes, then you need a signal system / automation upgrade. (Or a parallel line!)
As a New Yorker, I'm very jealous of Vancouver's SkyTrain system. ("But NYC has the best metro in North America!!" Maybe...) The NYC subway has a lot of peak hour capacity. I hate traveling at peak hours. So that means I'm always standing in stations waiting 10 minutes for the next train. If I lived in Vancouver, then that would be 3 minutes. Sounds good to me!
I also agree with the author in that I'm not sure what elevated trains did to hurt people. I lived in Chicago next to the L for years. It never bothered me. It's nice to see out the window and look at something while you're in transit. And it's cheaper than building things underground. NYC apparently got rid of its elevated railways because of snow, so that's something to watch out for. But Chicago gets more snow and it does OK. (Having commuted on both systems in the snow, it's a mixed bag. Chicago doesn't shut down, but it's slow as people remember how to deal with snow. NYC can run on snow-free underground tracks, but sometimes the governor is like "fuck it, I'm cancelling all the trains anyway" and then you're just stuck.)
SkyTrain vs Seattle Link Light Rail is a fascinating contrast.
SkyTrain works because of a virtuous cycle of attributes:
Full grade separation enables automation. Automation enables many trains per hour. Many trains per hour with short trains still has tons of capacity. Short trains means lower costs for stations, which as the article notes is a huge portion of rapid transit costs. Lower cost means building more transit for the same budget, so more transit gets built. More transit with great headways results in transit being the mode of choice. Take any one of these elements out and you can still have a functioning transit system, but the magic is missing.
Link light rail is so close to full grade separation but not quite there, so headways are limited by the grade crossing. With longer headways, bigger trains are needed to serve the same capacity. Bigger trains mean big stations and beefier, more expensive viaducts. Big stations are expensive.
Link is gaining ridership and offering great service, but it's hard not to think if they had learned the full lessons from nearby Vancouver it would be even better (and cheaper).
> I also agree with the author in that I'm not sure what elevated trains did to hurt people.
They're horrifically ugly for pedestrians and city life generally. If you've been around the elevated subway tracks in Brooklyn, for example, they're not pleasant to be around. They block out the sun, they're incredibly noisy, they make the street claustrophobic, they definitely become streets to avoid unless necessary.
Yes, they have a nice view if you're a passenger. But they make the city much, much worse for everyone below them.
> I also agree with the author in that I'm not sure what elevated trains did to hurt people.
You need to either build them in right at the start of a new development or you gotta demolish a lot of housing - similarly to what was done in a lot of US cities when the highways were built [1].
> I also agree with the author in that I'm not sure what elevated trains did to hurt people.
I've only seen them in Hamburg. They are generally an eye-sore. And the area underneath them is somewhat unusable (like any area under a bridge): you can't really build anything there. So it's an eyesore above an eyesore.
There are plenty driverless trains in operations. Some have been running for decades. For example Toulouse in France has a metro without drivers since 1993. I was there a decade or so ago and sat in the front of the train on a bench in the front of the train staring out into the tunnel. Because there isn't a driver compartment. Really cool. They have some fences on the platform that align with the train doors for safety. The train lines up, people get in/out and it drives to the next station. Some airports have similar systems. This stuff has been possible for quite some time.
These days, you should be designing for autonomous operation for new infrastructure. Much easier when you design from the ground up. Not doing that could be an expensive mistake.
I mean this is talking about construction of brand new lines, and in the Western world if you are building a brand new, totally separated line then automated is the no-brainer solution given high Western labor costs.
Readit News
Singapore built the orbital Circle MRT line exactly as the author wants: small trains (3 carriages, vs 6-8 on other line), small stations to fit these trains, frequent fully automated operation.
However, the line turned out to be much more popular than planners anticipated, with the result that at rush hour, it's common to have to queue just to enter the platform where you need to wait for multiple trains to arrive before you can squeeze in.
And the tricky bit is that there is essentially nothing you can do now to fix it. There's a hard physical limit (around 90 secs) on how fast the cycle of a train arriving, people getting on and off, and departing can get, and retrofitting all 30+ deep underground stations to be larger would be an insanely expensive and disruptive exercise.
You can build another line. This one was cheap and the demand is clearly there. And two medium capacity lines are generally better than one high capacity line in terms of offering more options to travelers.
Singapore's MRT lines are some of the most expensive public transport projects ever. The Circle Line, fully automated and fully underground, cost S$10 billion[1]. The recent Thomson-East Coast Line, still partially under construction, is projected to cost S$25 billion[2]. It was not 'cheap' by any means.
> You can build another line
Singapore is building another line: the Cross-Island Line[3]. It has planned or is constructing at least three more lines[4][5] to achieve something like 460 km by 2040, thereby exceeding the length of the London Underground. About S$100 billion is earmarked for public transport expansion.
But the Circle Line was, as someone who has used it ever since it opened in 2009, ill-conceived as a 'small line'. It is heavily overcrowded. Because of the immense traffic and somewhat lacklustre maintenance, it has suffered several delays and breakdowns. The ideal thing for LTA to do would be to expand each station's capacity, because it links all of Singapore's radial lines at heartland residential areas.
[1]: https://medium.com/from-the-red-line/was-the-circle-line-bui...
[2]: https://www.mot.gov.sg/news/Details/speech-by-minister-khaw-...
[3]: https://www.lta.gov.sg/content/ltagov/en/upcoming_projects/r...
[4]: https://www.lta.gov.sg/content/dam/ltagov/who_we_are/our_wor...
[5]: https://en.wikipedia.org/wiki/Mass_Rapid_Transit_(Singapore)...
My ideal default rapid transit buildout for midsized urban areas would basically be SkyTrain with value engineering to extend the platforms to 100 or 120m with minimal cost in the future.
But before this you had no idea that there was so much demand, right?
It's quite a lot easier to sell a huge monetary upgrade on something oversubscribed rather than a huge monetary outlay that may be a complete white elephant.
There is a good basis to this. Every new mile and station you add to a system compounds on the size of the system. The 11th station connects you to 10 places. The 51st station connects you to 50 places. Build small and you never get the critical mass needed to see widespread adoption.
There is a safe minimal distance between trains, in fact, a safe distance for a given speed. Shorter trains are not exempt from obeying it. You can make shorter trains more frequent at the expense of lowering traveling speed.
What is the cap of throughput is due to these speed limitations is an exercise left for the author of the article.
It’s the same with cars. A 2s headway with cars holding 1 person each means that the maximum capacity of a highway lane is 1,800 people per hour, no matter how fast they go (the cars are further apart at higher speeds).
They already did that exercise:
> 3-car trains running at 30-40 trains per hour (a normal peak frequency for automated or even some human-driven metro lines) reach a capacity of about 18,000 passengers per hour per direction, well above the expected demand of any American line that doesn’t go through Manhattan.
The fundamental constraint is not technology, but people and physics: you need to decelerate and stop, let people disembark and get on, accelerate and clear the platform. This cycle requires a bare minimum of 90 seconds, although IIRC a few lines in a few places like Paris and Moscow do 85 secs.
They took "30-40 trains per hour" out of thin air and exercise was to calculate whether it is even possible to have more frequent shorter trains.
Signaling systems used on automated trains know the position, speed and capabilities of every train. Keeping a safe distance behind isn't a problem.
Trains have the capability to accelerate and decelerate faster, we mostly don’t do so for comfort and safety reasons.
> Wait times are the second-most underrated component in making metro systems effectively faster (right after street to platform time).
Street to platform time made using public transit annoying in several Asian capitals. Wait times are the main reason why I often hate traveling with public transit even in a city with one of the best public transit systems - if you aren't planning your life around the transit schedule, the wait time is essentially an unpredictable part of your travel time (and if you do plan around it, it's one more annoying thing to deal with).
If you leave your doctor's office, and you have a 10 minute train home that goes every 30 minutes, then you really have a 10-40 minute train home - so for practical purposes, you essentially have a 40 minute train. Once unreliability or delays become frequent enough to start being a factor to consider, this could easily turn it into a 70 minute train.
Another big factor is the time between the actual start/end of the trip and the nearest station. Even with near-zero street-to-platform time (e.g. busses/trams) and reliable, reasonably frequent public transit, once you add it all up, a bicycle often ends up being faster than even excellent public transit.
Munich is planning on building a second subway route. It just does not have the money nor the space to build one. There has been discussion on building a second tunnel below the first, or on enabling the common train system for overflow by suburban trains -- by installing more signals to run more tightly packed.
[0] https://db-engineering-consulting.com/en/projects/munichs-se...
[1] https://www.youtube.com/watch?v=bPDQdnT-RaY
A simple example would be 3 services on the same line that follow a repeating pattern every 3 stations. ==[A]==[B]==[C]==[A]==[B]==[C]==. The service (AB) stops on the stations labelled [A] and [B] (skipping C). The service (AC) stops on the stations labelled [A] and [C] (skipping B). The service labelled (BC) stops on the stations labelled [B] and [C] (skipping A). In this manner, all three services skip over 33% of the stops on the line, but no matter what your origin and destination, it is always possible to travel from an [A] station to a [B] or [C] station (or another [A] station), and likewise from a [B] or [C] station.
To the extent I've worked out the logistics of this, if you allow for trains to catch up but not pass each other at the platforms, you can push this idea as far as only stopping at 2-in-5 stations without sacrificing headways or capacity.
Just a weird thing thats been taking my attention lately.
As for short trains on long platforms, this is pretty common in NL where the bigger train stations can support both very long international trains and shorter local trains on the same platform; a train can switch to a center track halfway on the platform.
I don't think it would really work for a subway system; people expect it to be hop on, hop off. In some places the stops (or people's final destinations) are so close together they can choose to get on/off earlier/later, but this system makes that less viable. You'd have more people shuffling through train stations trying to figure out which train to get or whether they need to wait for the next one, also putting extra load on staff for confused not-locals. And finally, you'd need extra rails or tunnels so that a train can pass another.
In terms of needing extra track, that's the brilliant part of it. Even though the different services all make different stops in my proposal, so long as they depart in a certain order they will never need to pass each other.
In the 2-in-3 stops example I gave, suppose that at the present moment there's an (AB) train at station [A], a (BC) train at station [B], and a (AC) train at station [C].
If they all depart at the same time then (AB) goes one stop to the next [B] at the same time as (BC) goes one stop to the next [C] and (AC) goes one stop to the next [A].
Then they should all depart again at roughly the same time (since they all presumably took the same amount of time to go one stop).
So (AB) goes two stops from [B] to the next [A] station at the same time as (BC) goes two stops from [C] to the next [B] station and (AC) goes two stops from [A] to the next [C] station.
Then the cycle repeats.
All three service run at the same time without ever catching up or passing each other.
If you use my two-boarding-area trick then the constraint can be loosened to allow different services to catch up (but not pass) each other, which then makes it possible to run 2-in-5 stops without adding a passing track.
To elaborate a bit, on the face of it the 2-in-5 system has 10 different services running on the line at the same time, because there's 10 possible unique combinations of 2 out of 5 things.
However, just like in the 2-in-3 example, many of these services can be run at the same time without passing or catching up because they are scheduled to move and stop in the same pattern (just offset from a different starting station.
Every single train in the 2-in-5 system can be categorized as either moving 1 stop then 4 stops, or moving 2 stops then 3 stops. Two services in the same category never catch up or pass each other. If you have two subsequent services in a different category then they simply take turns catching up and falling back behind (but ultimately never passing each other).
Here's a (rough) line diagram I calculated showing where each train is at every 3-min interval in the 2-in-5 system. Notice how they meet but never pass.
https://ibb.co/4R9nQsQd
In terms of confusing people and knowing which train to get on, this is what I've come up with as a signage convention. All that's necessary to know what train to get on is the symbol on the map of your destination. If a train has the same symbol on it then it goes there.
https://ibb.co/tpjzJdyR
Consider a metro system with trains 70 m long. With 10 m of space between the two boarding areas, that means the length between both sides of the station is 150 m. If the entrance to the platform is in the center, the walk to the middle of each boarding area is 45 m, taking about 30 seconds. If the entrance is at the end, that becomes 35 m or 115 m (taking about 20 to 90 seconds to walk). I think those figures are comparable to the dwell time of a typical metro system.
I do think it's a very interesting idea though! I think it'd work better for longer trains over longer distances, where the time spent accelerating and braking is often greater, but unfortunately few places are even considering anything shorter than 15 minute headways for such rail services.
So in a 2-of-5 stopping pattern you'd save 3 min every 5 stops, but depending on when arrive at the station you will sometimes get unlucky and just miss your train, in which case you'll have to wait an additional interval than you normally would for the next one (costing you 3 min). So for very short trips (under 3 stops) it actually makes travel time a bit worse since there's very few stops you can skip over in such cases. But for more median trips there is a saving, and for the longer trips it saves well into 2-digit minutes.
In your example I think in the case with the entrance at the middle of the platform there wouldn't be any real effect, because splitting the platform also in the middle doesn't marginally change how quickly you can get to the nearest open door on the train you want. There's no real need to get to the center of either boarding area. In the case of platform at the end of the station, I can accept that adds about 40 m of walking distance that wasn't there before (at least for some people), and that translates into an extra 20ish seconds. Less than that if you do the rational thing of walking briskly when you see you're about to miss your train.
So you're right that the platform split adds some time which isn't completely negligible, and depending on what fraction of the next n stops you want to skip it comes at a penalty of longer wait times for the correct train, but both of these are fixed upfront costs whereas the dividend accrues linearly the longer your on the train.
You will also find long trains that split in half mid-journey, so you need to make sure you get in the right car or you'll go to the wrong place.
Edit: I guess it's not exactly what you're saying, in Europe you will find platforms split into several sections with multiple trains to board, but they'll be for different lines with different destinations.
https://en.wikipedia.org/wiki/Skip-stop
This lets you schedule them much closer together than the conventional 3 min while still being safe.
Others have already pointed out some of the practical things that would limit what you can achieve with shorter trains like minimum headway between trains and the congestion that would occur after a delay where you would expect people to wait for maybe 10 short trains to arrive and depart before you could get on.
There are other problems. The cost of the smaller trains means if e.g. 2 carriages each, then every other car is a driving vehicle with motors and control equipment. On longer trains, this could be 1 in 3 or 1 in 4. Each of these not only requires regular maintenance (so that's doubled the maintenance requirements) but also creates massive congestion issues in maintenance yards. Commonly, 1 or 2 full trains fit in each siding so getting most trains out if e.g. one is broken down is usually easy enough. Imagine having to move 3 or 4 separate smaller trains out of the way, they are not automated in the yards.
Most people would be very unhappy knowing that they might be alone on a train, which is a main reason why operators are not quick to get rid of all staff. But currently, a single driver and conductor is close by for, maybe, 8 carriages. This would double if you needed a single attendent on each 2 carriage train.
The signalling is very heavily designed around traditional trains with its delay after passing a signal. 4 x 2 carriage trains would utilise more signalling capacity/time than 1 x 8 carriage train. If these were all coming from the same location and needed to return, that would also need a lot more platforms so that the following trains don't block the first trains in terminal platforms. This is already a major problem at most UK terminal stations so that is largely unsurmoutable.
I also heavily question the idea that station cost is largely dependent on platform length. On most surface stations, platforms are relatively easy to construct and whether they are 4 carriages or 12 carriages long still require a station building or 2, some ticket machines and CCTV etc. For elevated railways that is more likely to be true maybe.
So yeah, like someone else said, we are unlikely to come up with ideas that 1000 other engineers haven't already asked, the easier problems to solve are around planning, design, legal rights for infrastructure projects etc. since these tend to eat up sometimes decades and billions of dollars.
That said, full automation is a major game changer because it enables short trains with high frequency which you would otherwise struggle to afford. Don't build light rail, build light metro which is a small cost more (build a metro with light rail) but now you can have full automation.
Depending on the system in questoin, this might be impractical or impossibly dangerous.
You can see whether the problem is being cheap or if it's actually a capacity issue. If weekend service sucks but peak hour service is good, then it's just being cheap. If rush hour can't handle passenger volumes, then you need a signal system / automation upgrade. (Or a parallel line!)
As a New Yorker, I'm very jealous of Vancouver's SkyTrain system. ("But NYC has the best metro in North America!!" Maybe...) The NYC subway has a lot of peak hour capacity. I hate traveling at peak hours. So that means I'm always standing in stations waiting 10 minutes for the next train. If I lived in Vancouver, then that would be 3 minutes. Sounds good to me!
I also agree with the author in that I'm not sure what elevated trains did to hurt people. I lived in Chicago next to the L for years. It never bothered me. It's nice to see out the window and look at something while you're in transit. And it's cheaper than building things underground. NYC apparently got rid of its elevated railways because of snow, so that's something to watch out for. But Chicago gets more snow and it does OK. (Having commuted on both systems in the snow, it's a mixed bag. Chicago doesn't shut down, but it's slow as people remember how to deal with snow. NYC can run on snow-free underground tracks, but sometimes the governor is like "fuck it, I'm cancelling all the trains anyway" and then you're just stuck.)
SkyTrain works because of a virtuous cycle of attributes: Full grade separation enables automation. Automation enables many trains per hour. Many trains per hour with short trains still has tons of capacity. Short trains means lower costs for stations, which as the article notes is a huge portion of rapid transit costs. Lower cost means building more transit for the same budget, so more transit gets built. More transit with great headways results in transit being the mode of choice. Take any one of these elements out and you can still have a functioning transit system, but the magic is missing.
Link light rail is so close to full grade separation but not quite there, so headways are limited by the grade crossing. With longer headways, bigger trains are needed to serve the same capacity. Bigger trains mean big stations and beefier, more expensive viaducts. Big stations are expensive.
Link is gaining ridership and offering great service, but it's hard not to think if they had learned the full lessons from nearby Vancouver it would be even better (and cheaper).
They're horrifically ugly for pedestrians and city life generally. If you've been around the elevated subway tracks in Brooklyn, for example, they're not pleasant to be around. They block out the sun, they're incredibly noisy, they make the street claustrophobic, they definitely become streets to avoid unless necessary.
Yes, they have a nice view if you're a passenger. But they make the city much, much worse for everyone below them.
You need to either build them in right at the start of a new development or you gotta demolish a lot of housing - similarly to what was done in a lot of US cities when the highways were built [1].
[1] https://www.reuters.com/world/us/us-freeways-flattened-black...
I've only seen them in Hamburg. They are generally an eye-sore. And the area underneath them is somewhat unusable (like any area under a bridge): you can't really build anything there. So it's an eyesore above an eyesore.
These days, you should be designing for autonomous operation for new infrastructure. Much easier when you design from the ground up. Not doing that could be an expensive mistake.