When using public transport, we often need to change routes in the middle of the journey. These changes have costs – I can think of the following, but there may be more.

  1. If we're reading, working, etc. on board, we need to take a break, losing flow.
  2. We spend time moving from one route to the next.
  3. We spend time waiting for the next departure.
  4. There are lots of passengers moving between routes. They take up space and cause queues when on- and off-boarding. This also increases the risk of accidents.

As far as I can understand, we could decrease the necessity of route changes by having multiple routes to the terminals (final stations).

I've reviewed the subway maps of London, New York and Oslo, finding that none of them do this to any significant degree – the terminals usually have just one route.

As an example, let's look at the simplest of the three – Oslo:

enter image description here

Imagine that you're travelling from Østerås (orange, left) to Ellingsrudåsen (orange, right). No changes required – route 2 takes you all the way.

But if you're travelling from Østerås to Mortensrud (purple, bottom right), you would have to change trains from route 2 to route 3 at some point.

Let's imagine that we use some of the capacity used for routes 2 and 3 to serve routes 6 and 7. Route 6 (gray) serves Østerås-Mortensrud, and route 7 (brown) serves Kolsås-Ellingsrudåsen:

enter image description here

With this design, some route changes can be avoided. If we added enough routes, many more route changes could be avoided. Granted, we would have to wait longer for a route that went exactly to the station we want to go, but we would always have the option of taking the first train and then changing like before.

So, I've been asking myself, why don't public transport authorities do this? These are the reasons I can think of:

  1. Simplicity for passengers: When only one route serves a particular station, you don't have to think about which route you'll board. Also, the maps would be more chaotic.
  2. Simplicity for transport providers: More routes would mean more difficult (and therefore costly) planning and management.

From my (admittedly ignorant) perspective, the above reasons don't seem sufficient to outweigh the advantages of fewer changes. Have I overlooked some problems with adding more routes? Or am I underestimating the costs and/or overestimating the benefits of more routes?


The main reason is economics. Who is going to pay for all the additional lines? The other part to this is, will the additional lines have enough passengers to make them profitable and sustainable?

If the lines are on the Earth's surface how much land will they occupy and could the land be better used for something else? If the lines are underground, or above ground, using elevated tracks, all this adds to the capital cost of the system.

Also, how much extra disruption would the additional lines create in terms of noise, vibration, aesthetic degradation to the environment?

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    $\begingroup$ I'm not suggesting adding more physical lines. I'm suggesting using the existing ones differently. $\endgroup$ – Yngve Høiseth Mar 2 '18 at 22:21
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    $\begingroup$ 2 and 3 already use the same physical rail, and what OP wants can be accomplished in "software" as it were. $\endgroup$ – Harper - Reinstate Monica Mar 4 '18 at 6:23

Keep drawing combinations. You forgot Østerås to Vestli, Østerås to Bergkrystallen, and every other combination of possible origin and destination.

This breaks down in a hurry. By the time you split up all the trains to hit every destination, you end up with only a few trains a day going where you want to go. Since you don't want to travel then, you wind up taking a 33 Østerås-Vestli then transferring at Majorstuen to a 21 Frognersetern-Mortensrud run. You still don't avoid the transfer, only now everything's more complicated.

Transfers are the better way

Maybe you haven't tried this run, but when you have a binary pair of lines like the ones you are looking at -- the far-and-easist way to provide all the routes you want it the timed, across-the-platform transfer.

Line 2 and 3 trains pull up at the same time to an island platform - the kind with tracks on each side. They sit there, 30 feet apart, with their doors hanging open for 20-30 seconds. Then when all the shuffling is done, the trains depart.

That might happen at the first place they meet, Smestad, or it might happen at one of the downtown stations where there's platform space to do this. You just walk 30 feet and sit down in the other train and done.

After that designated transfer station, transfers are not guaranteed. They might roll into Hellerud abeam. You might be able to bolt across. I've done it. But it's not a guaranteed timed transfer - if the other train slams the door in your face, tough beans.

The only downside to this is when the routes are coincident for a good length, as in this diagram. This means people traveling within the overlapping section have twice the wait for two redundant trains. It makes sense for them if the two parallel lines (4 in your diagram actually) stagger themselves so the core zone gets very frequent service if you don't want to go past Brynseng.

  • $\begingroup$ Thanks for introducing me to the idea of timed, across-the-platform transers – that's a great idea. However, its relevance depends on the infrastructure (the existence of island platforms). > […] You still don't avoid the transfer, only now everything's more complicated. I think some people would avoid the transfer. If so, the question becomes, is it worth the extra complication? It's an empirical question, and I don't think its answer is at all obvious. $\endgroup$ – Yngve Høiseth Mar 9 '18 at 14:25
  • $\begingroup$ @YngveHøiseth Timed transfers done right are a thing of beauty. Yes, Norway has superb rail transit, but if they have all split platforms in that central corridor (no islands) - that doesn't work for timed transfers, handling people with limited mobility being the ugliest problem. At that point they might as well interleave/stagger trains. Another design mistake is making things so complicated you need a timetable to figure it out. Ideally anyone just walks down to the station and there's a sane wait, or at least have a memorable schedule like :03 and :33 after the hour. $\endgroup$ – Harper - Reinstate Monica Mar 9 '18 at 15:59

Best guess to the problem of adding more: Logistics and economics. First of all, never underestimate the cost of public construction project such as tunnel buldinnstuff. The last sizeable expansion was the Løren-banen which was finished a couple of years ago. The short stretch between Sinsen and Økern ended up costing more than 1 billion NOK (Google, 2018). An aspect regarding the logistical side of this can arise when you cross lines. F.X. there will probably be complications that will result in longer queues in the tunnels between the stations when you have to change tracks, specially when a train is already running late which is something that is known to happen every now and then. But I completely agree that there are great benefits for doing this. An example would be the mentioned Løren-Line which made life a lot easier for those of us that live on the wrong side of the Akersriver

Litteraturliste: Google. (2018). Google search engine.

  • $\begingroup$ I'm not suggesting adding more physical lines. I'm suggesting using the existing ones differently. $\endgroup$ – Yngve Høiseth Mar 2 '18 at 22:22

Given that the six parallel lines in the centre of town actually consist of only two tracks (one eastbound and one westbound) running through "the tunnel" (Oslo T-bane or Oslo Tunnelbane) and that points or switches exist at the appropriate points (which they must to allow the existing route options) then your idea is possible.

enter image description here

Figure 1. Stortinget station, Oslo. Source: Wikipedia. Note that there are only two tracks.

The lines can handle 24 trains per hour in each direction giving a 2.5 minute headway (separation between trains). This is the system bottleneck.

The convenience of the multiple direct route options must be contrasted with the simplicity of the single-route system. "Take the red line to X and then take the blue line to Y" will always work. With a 2.5 minute headway the timetable could be designed around a repeating pattern so that the offset between trains is predictable. This may allow passengers to commit the pattern to memory and know that there is a train at 2, 17, 32 and 47 minutes past the hour, for example, and that the journey will always take the same time.

The rolling stock is all the same type so there should not be any physical reasons why trains are restricted to one route.


If I were working at the public transport authorities office, my main concern would be the added complexity for travellers that you already mention.

Your suggestion would require more from travellers in terms of planning and understanding and would (I suspect) increase the probablity of some personality types not getting to their desired destination on time.

I can see the benefit of more routes for travellers more inclined to plan and reason, but for others I'm not entirely sure that the reduced cost of less changes would outweigh the costs related to confusion, backtracking and/or delays in getting to the desired destination.

I am aware that this might just be me underestimating travellers. But then again, the same might the case for the transport authorities.


Imagine this simplified scenario:

  • You have 4 stations: A, B, C and D.
  • There are 2 trains, one is travelling only on line A-B and the other on line C-D.
  • There are 2 people at station A – one wants to go to B and the other wants to go to D.
  • There are 2 people at station C – one wants to go to B and the other wants to go to D.

enter image description here

The passengers at A both hop on train A-B and those at C hop on train C-D. When the trains meet at the central line, the passenger on train A-B wanting to go to D switches to train C-D and the passenger on train C-D wanting to go to B switches to train A-B. Then the trains continue to their respective stations and drops everyone off.

If each passenger is lazy and doesn’t want to switch trains, You’ll either need to invest in double the amount of trains, or each passenger will need to wait twice as long for his/her train because the trains need to switch routes between each cycle to satisfy the passengers.

Seeing that mandatory stops are made on the central line where people will hop on and off the trains in anyway, why not use this opportunity to optimise the rest of the system?


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