A few years ago, Sandy Johnston remarked that Jerusalem had the least gridded street network he ever saw, and this complicates any surface transit planning there. At the time he was familiar with New England already, but Jerusalem seemed different.
Here are street maps of West Jerusalem and Boston, at the same scale:
Boston has some gridded sub-areas, like Back Bay, but Downtown Boston is as messy as Jerusalem, and on the level of arterial streets, even the rest of the city isn’t too different. The real issue affecting Jerusalem is the hilly topography. Once one gets out of the core of West Jerusalem, the city turns into a mess of hills with internal street networks and poor connectivity between them. Boston maintains a coherent structure of arterial streets that host buses and tramways, with a cobweb structure that feeds the subway efficiently; in Jerusalem, there is little chance of that.
Surface vs. rapid transit
Rapid transit is mostly insensitive to hills. A subway can be built across hills, partly underground, partly elevated. This is the case in Upper Manhattan, where the 1 train runs in a mix of cut-and-cover subway, elevated structures, and mined deep-level tunnel.
Even if the hills slope down into the natural arterial, this is not such a problem. Train stations can incorporate escalator access and have exits at different elevations. New York manages this in the same neighborhood where the 1 runs, in Washington Heights, on the A train. Monaco, on a sloping hill, manages the same at its train station, which is located underground, using elevator access from multiple neighborhoods at different altitudes.
The deep mining required for such construction doesn’t even raise costs that much. If it’s possible to secure horizontal access to the station site, construction becomes easier. Moreover, running elevated through the valleys, as the 1 does in Manhattan Valley and Inwood, cuts costs rather than increasing them.
Evidently, the hilliness of Rome has not prevented the city from building a subway. Line C’s construction costs were very high, but not because of topography but because of millennia-old archeology, which is not really a question of the street network.
Since rapid transit is not affected as much by hills as surface transit, a city with hilly topography should be biased toward rapid transit and against surface transit. This does not mean every flat city should be content with surface transit and every steep city should build subways and els, but it does mean that the population and density thresholds for rapid transit are smaller in hillier cities.
Some cities are very hilly, but this does not affect their street networks. San Francisco is famous for this: north of Market, in neighborhoods like Telegraph Hill and Russian Hill, the street grid continues mostly uninterrupted, and the result is famously steep streets. In these cities, transit network planning need not pay much attention to the topography: the only concession that need be made is that agencies should preferentially electrify and run trolleybuses, which have better hill-climbing performance than diesel buses – as San Francisco Muni in fact has, retaining trolleybuses rather than replacing them with diesels as nearly all other American cities have.
The more interesting and difficult case is when the street network respects the hills. It can naturally turn the city’s street layout into that of multiple distinct pods, each surrounding a different hill. This is popular in Jerusalem, especially the settlements within East Jerusalem, but also in some of the newer parts of West Jerusalem. There is not much connectivity between these different pods: there may be a single arterial road with the rest of the city, as is the case for the settlements of Pisgat Ze’ev, Ramot, and Ramat Shlomo.
This kind of pod development is popular in a lot of auto-oriented suburbia. The cul-de-sac is a defining feature of many an American suburb. However, in Jerusalem we see it happen even in the context of a dense city: Jerusalem proper has a density of 7,200 people per square kilometer, and all the settlements in question are within the jurisdiction of the city. It comes out of a combination of modernist central planning (Israeli neighborhoods and cities are designed top-down, rather than expanding piecemeal as in North America or France) and the hilly terrain.
Transit planning for such a city is a chore. In theory, choke points are good for transit, because they have high intensity of travel, where dedicated lanes can make buses very efficient. In practice, choke points work for transit only when there are coherent corridors on both sides for the buses to feed. For example, on a wide river spanned by few bridges, buses can run on the bridges, and then continue on the arterials feeding them on either side. Pod development, in contrast, has no coherent arterials within each pod, just collector roads feeding the main drag. Buses can still run on these streets, but there is no structure to the density that encourages them to serve particular locations and not others.
One solution is a type of transit that is overused in flatter cities: the direct express bus, or open BRT. This bus runs local within each pod and then continues on the arterial, making few stops; it could run as open BRT if the arterial has enough development to justify such service, or as a nonstop express service if it is a full freeway. This form of transit developed for both low-density American suburbia and Israeli pod development towns (where this is buttressed by the tendency of the ultra-Orthodox to travel in large families, in which case transfer penalties are much higher, encouraging low-frequency direct service).
Another solution is to go in the air. Gondola lifts are seeing increasing use in extremely hilly cities, where surface transit must wend its way through switchbacks. Medellin’s Metrocable has a vertical rise of 400 meters. Even in cities that are less steep, gondolas could be a solution if arterial roads are simply not available. In the Arab neighborhoods of East Jerusalem, arterials are rarely available, and gondolas bridging ravines could be of use. Gondolas could also be useful for neighborhoods that are only connected by arterial in a radial rather than circumferential direction – they could again bridge ravines to connect peripheral neighborhoods to one another rather than just to the center.