Lagos is the second-largest city in the world without rail rapid transit (the largest is Karachi). Sources disagree on its population, but it looks like 21 million in the built-up area, consisting of most of Lagos State plus a few suburbs just outside it, such as Ota and Ijoko – in total, 1,000 km^2, someone more including the suburbs. All of the problems that rapid transit intends to fix – traffic jams, pollution, long commutes, overcrowding, unpopular jitneys – are present. I don’t want to repeat the case I made in this post in favor of aggressive investment in subway systems in Lagos and other big third-world cities. Instead, I want to talk about concrete features.

Here is the map – it’s slightly different from the version I circulated in previous posts. Note the following features:

1. Four of the lines – East-West (blue), Main Line (red), Ikorodu (brown), North-South (purple) – are four-track. This is because Lagos is so big that its outer margins require very wide stop spacing, which requires four tracks. The first three also run in wide enough rights-of-way for significant stretches, making four-track elevated structures easier to construct. Express stops are denoted with squares, local ones with circles. If two four-track lines intersect, the stop is denoted with a square, and is express for both lines. All four-track lines have two-track tails – the farthest-out square is the last station with four tracks, where locals turn, while expresses keep going to the end. Only one four-track line has an end without a tail: the Main Line terminates all trains at Leventis.

2. On the four-track stretches, the average interstation is a little less than 4 km. Average speed can approach 60 km/h, given that the rights-of-way are often quite straight. On the local tails of these lines the average looks like 2 km, or around 50 km/h. On the two-track radial lines, the average interstation is a little less than 1.5 km, or around 40 km/h; the difference with the local tails of the four-track lines is that the local tails are in suburban areas.

3. Every pair of radials intersects, usually in Lagos Island but sometimes elsewhere. Four circumferentials – Apapa (dark red), University (ochre), Ishaga (dark green), Idimu (magenta) – intersect all the radials. Whenever two lines intersect, there’s a station. Doing this requires a lot of lines to run in the same alignment in the center. This is not track sharing, but multi-track tunnels. The only eight-track tunnel, where the Main and Ikorodu Lines run together between Eko Bridge and Leventis, has a wide road to go under; the only ten-track el, where the East-West, Ota, and Ikorodu Lines parallel around the National Theatre, has an entire expressway to go over.

4. The southern ends of the Ota (yellow) and Ikeja (silver) Lines are in open water today. This is because the area is slated for land reclamation and intense development, called Eko Atlantic. The western margin of that area, around the station I call Eko Atlantic, is already reclaimed, but still undeveloped. That entire area (Victoria Island) is the favored quarter of Lagos, and is commercializing; farther east, in Lekki, there are grand plans for suburban redevelopment, and an immense amount of casual marketing in the media (“buy now and the land will triple its price in five years”).

The system I’m proposing differs from the current proposal. The current proposal only has five radials (with apparently just one crossing from the Mainland to Lagos Island), corresponding to my East-West Line, Main Line, Ota Line, and a hybrid of the Ikorodu Line and the two branches of the North-South Line; there is one circumferential, vaguely corresponding to my Idimu Line.

Some of the features of the current proposal are a good start. It’s not possible to build eighteen lines at once, and some prioritization is required. It’s even fine to start with shared tracks into Lagos Island and subsequently give lines their own way into Lagos Island. (On my map, everything paralleling the three existing road bridges is a bridge, the rest are tunnels).

However, the existing proposal suffers from several shortcomings, which will need to be fixed later:

• The stop spacing is too wide even in the center, intermediate between my local and express tracks.
• There is far too much branching. In any reasonable sequencing of the lines, the East-West Line will fill before the later ones (i.e. the ones going north-northeast) open, requiring new routes into Lagos Island.
• There isn’t enough service in Victoria Island, which is developing as a CBD, as is common for rich neighborhoods.

But the worst problem is that the under-construction route goes elevated along the Ring Road, skirting Lagos Island, with just two stops, Ebute Ero and Marina. This segment has little value and should be demolished once direct underground routes with more stops open. According to a paper that’s no longer online, one of the reasons third-world subway lines tend to underperform ridership expectations is that many of them use available rights-of-way and skirt the CBD, instead of building short tunnels to get to the center. This paper in turns is one of the references used by Bent Flyvbjerg in his paper arguing that in general urban rail has cost overruns and ridership shortfalls.

The big obstacle for constructing any subway system is cost. This is especially true in Lagos, where the construction cost of the current project (the Blue Line, corresponding to the inner part of the western half of my East-West Line) looks like $180 million per km, entirely elevated. I say “looks like” because while the cost is consistently $2-2.4 billion in exchange rate terms (around $5 billion in PPP terms), it’s not completely clear whether this is the Blue Line or also the Red Line.

My proposal is largely elevated, but the Lagos Island segments have to be tunneled. So do some other segments, for examples the inner parts of the North-South and Ikeja Lines, and most circumferentials. The system, totaling about 900 km, of which 200 is four-tracked, looks like it could be built only about one-quarter underground, or slightly more. Moreover, much of the underground construction could be cut-and-cover, including several segments in Lagos Island, and most of the circumferentials; only the underwater crossings and a few off-grid Lagos Island connections have to be bored.

The main analytic point here, carrying over to other cities, is the importance of prior planning. My map has 18 lines. This is useful because figuring out where stations should go, which stations on four-track lines get to be express stops, and how to sequence the lines should be based on long-term considerations. As I hinted in a post written right after I finished the first version of this map, about subway lines that intersect without a transfer, building the best lines 1-3 requires having a good idea where lines 4-12 will go. So even if Nigeria runs out of money after the first two lines are built, figuring out the built-out network is not useless – it informs the current network, and makes adding future lines less painful.

This is true for reducing construction costs, and not just for a good network. One of the positive features of the Paris Metro is that nearly all of it was planned as a whole, and as a result, difficult stations like Chatelet, Etoile, and Nation were built with the intention to have multiple Metro lines serve them. This meant that the stations could be built once, rather than multiple times, once for each line. Two lines, Metro 8 and 9, even run alongside each other for 1.7 km under the Grands Boulevards, which are wide enough for a four-track subway.

The planners of every system, regardless of whether it’s a metro for a city that doesn’t have any urban rail or an extension in a city with fifteen lines, should always think ahead. What are the future plans? What are the future needs? What is the expected future growth? In Lagos, the answer to the last question is “fast demographic and economic growth,” and this means the city should plan on a large system – hence my almost gridlike system of radials going north and northwest and circumferentials crossing the Mainland going southwest to northeast. But really, every city needs to ask itself how it wants its rail network to look, and plan the highest-priority segments accordingly.