The Difference Between Bus and Subway Alignments

Reading design guidelines for bus routes reminds me of how different surface transit is from rapid transit. Buses need to follow straight, wide, two-way roads. Subway trains do not: those roads make construction easier, but it’s normal for train lines to detour and turn, even in rigidly gridded cities like New York. The upshot is that sometimes the optimal route for a bus is different from that of a subway, and this limits the usefulness of preexisting bus routes for subway planning.

For a relatively simple example of this, consider the plans for a subway under Wilshire Boulevard in Los Angeles. The buses follow Wilshire all the way from Downtown to Santa Monica. The trains were never intended to: there’s a short stretch where Wilshire isn’t as important while somewhat off the street lies Century City, and all alignments studied for the Wilshire subway have involved some deviation. The chosen alignment is the one that deviates more than the other, to serve Century City more centrally.

This is relevant specifically to the example of Tel Aviv. When I criticized the Tel Aviv subway route choice for being politically motivated to avoid certain neighborhoods, Alan of Tel Aviv Bus Mappa said,

To minimise cost, the planners looked at what works today (the existing high-demand bus routes) and decided that connecting Petah Tikva and Bat Yam to Tel Aviv was the highest demand corridor. They also looked at what was wide (boulevards and arterials), as their aim was to maximise segregated on-street running. This is also the reason that the plan makes use of the ‘Turkish line’ alignment connecting Jaffa and Allenby rather than the more direct, but narrow, Derech Yafo and Eilat Street.

Central Bus Station would have been a huge diversion for the route and is not a particularly in-demand destination. However, the planned Green line will serve that location.

The problem with this line of thought is that subways are not buses. Subways can use the more direct but narrower alignments if they need to: it may be somewhat more expensive to construct, but there’s no disutility to passengers. A bus running on a narrow street is slowed down, especially if the street is twisty. A subway that can go under private property is not.

Even in New York there are some twists – for examples, the route of the L through Brooklyn, and the route of the 2/3 from the Upper West Side to Harlem. But those twists are not critical, and the city doesn’t really need them. The Wilshire deviation in Los Angeles is also in this category.

It’s ungridded cities where the ability of trains to cut under the street network becomes critical to providing service to major destinations, which may not be anywhere near the wide streets. A look at the inner network of the London Underground will confirm that the lines bear little relationship to the street network, which was built incrementally over the centuries and would not be good at serving the major destinations in the desired directions. In Paris the older lines were built subsurface and do follow streets (which at any case are more rationalized than in London due to heavyhanded central planning), but the newer ones were built deeper and do not.

In Tel Aviv, the problem is that many of the neighborhoods that need public transportation service the most do not have wide streets for buses, or have wide streets configured in the wrong directions. The oldest parts of the city, the Old City of Jaffa and Ajami, have very narrow streets since they predate modern boulevard design by a few centuries. The next oldest – the Jewish neighborhoods of Jaffa, South Tel Aviv, the western parts of Central Tel Aviv, and the Old North – do have wide streets, but often pointing in the wrong direction, for examples nothing serves the Port or the Basel Heights compound, and the east-west streets going through the Old North are very narrow. They have no reason to form a coherent rapid transit network, since they were built as interurban streets or as neighborhood main streets, not as subway alignments. They barely even form a coherent bus network, but the hacks made over the decades to create bus trunk lines are different from the optimal route a subway would follow.

In fact, the recently-reelected Huldai administration has plans to upzone around the central parts of the route to build a new CBD. The area in question, around Begin Road, is unwalkable and almost unfixable to be made pedestrian-friendly, the road is so wide and fast. This is not service to an existing destination that follows a linear corridor as in New York and other strongly gridded cities.

In a city like Tel Aviv – or any other city without a strong grid that influences development – subway planning should start from a list of major destinations and dense residential neighborhoods and their locations on a map. The subway routes should form somewhat straight lines connecting them, with the first line chosen in a way that connects to the most and the most important ones. It’s fine to have somewhat kinked routes – nobody likes riding a C-shaped route, but it’s okay to have small deviations such as the ones proposed for Wilshire or even larger ones such as the one Shanghai’s Line 1 takes to reach People’s Square. The junctions should be the most important destinations, or the ones with the most potential for CBD formation; in Tel Aviv those are generally to the west of the planned CBD, because of the potential for waterfront upzoning and the preexisting density in the neighborhoods south of the Yarkon and west of the Ayalon Freeway.

Buses are of course not planned like this. A city that wants a vigorous bus network needs to do what Los Angeles and Vancouver have done: put the buses on a grid as much as possible, and have them go straight along major roads, with as few deviations as possible. Vancouver’s north-south buses deviate a little bit to serve Downtown, and even those deviations are sometimes questionable since people transfer from the buses to SkyTrain before the buses reach Downtown. The grid allows for an efficient network of transfers, with the transfer penalty reduced by high frequency on the trunk lines. It’s nothing like subway lines, which form a tight bus-like mesh in about one city in the world (Mexico City) and everywhere else have a mesh-like core surrounded by what is an essentially hub-and-spoke system.

Even when the busiest bus routes do indicate something about subway demand, there are exceptions. In New York, the busiest bus lines today are the M15, on First and Second Avenues, and the B46, on Utica Avenue: they are almost even in ridership and have traded places for first place citywide recently. But nobody expects a Utica subway to get the ridership of Second Avenue Subway, even people like myself who believe such a subway is underrated and should be considered in medium-term transit planning. The third busiest route in New York is the Bx12, on Fordham, and I do not know a single transit activist who believes it should be railstituted, even ones who believe other routes with somewhat lower ridership should be railstituted (such as Nostrand, whose bus, the B44, ranks fifth). The issue here is that First and Second are in Manhattan, where bus speeds are so low that ridership is suppressed, as people walk longer distances to the parallel subway or don’t take the trip; if both Second and Utica get subways, the lower amount of congestion in outer Brooklyn is irrelevant and the trains will travel at the same speed, whereas today there are factors working against Second that make the rail bias there higher than on Utica.

Something similar is the case in Tel Aviv. The widest boulevards have the largest concentrations of bus trunk lines, but that’s because they are the only streets on which buses are even remotely feasible as modes of transportation. In Jaffa, Jerusalem Boulevard is wide enough for fast surface transit but Yefet Street is not. Based on Jerusalem’s width, the planners chose to keep trains at-grade on Jerusalem, which they could not do on Yefet. But if trains were underground, Jerusalem’s current advantage would evaporate, leaving Yefet with the advantages of proximity to the Old City and the Flea Market and of higher density.

It is wrong to plan buses as if they were subways or early-20th century streetcars, where frequent twists were not a problem since there were few cars on the road, and where the dominance of the traditional downtown favored a hub-and-spoke network. Recent bus successes in North America have involved discarding those ideas and planning buses based on modern travel needs and modern traffic levels. By the same token, it is wrong to plan subways as if they were buses when they are capable of following alignments that buses cannot.

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16 Responses to The Difference Between Bus and Subway Alignments

  1. Rob Durchola says:

    Question: Would building subways in Tel Aviv risk significant delays in construction (especially in older neighborhoods) because of historic artifacts and sites being uncovered/identified?

  2. Joseph E says:

    You are right that subway alignments have more freedom to pick the best routes and destinations. And since they can be fast and high-capacity corridors, it is important to plan for transfers to buses or other lines at either end, where in a bus-only system you can do best by limiting transfers to 1 or 2 per trip.

    But in an ideal system, the principles that lead to good bus routes often work for grade-separated rail:
    1) There are still benefits to following major public right-of-ways, like major streets or rail corridors, because there is no need to pay for right-of-way, and no risk of tunneling under existing or future buildings. If the right-of-way is wide enough, you can save money especially at stations by building as shallow as possible with cut-and cover, or by elevating the line instead of going under.

    2) It still makes sense to keep subway routes as straight as possible; straight lines get from point A to point B faster, they are cheaper to build, and cheaper to maintain than curves.

    3) A grid or network of routes is still ideal. Paris and Tokyo have a complete net of subway routes, which makes it possible to get almost anywhere in the core of the city with only 1 transfer (perhaps 2). If a city cannot afford a complete grid of subways, then the few subway lines will need to work with a grid or network of transit lines to bring people to the subway, and to serve the rest of the city. A simple grid with is the most efficient way to do this.

    I can’t speak about the planning in Tel Aviv. But from what you wrote, I wonder if the goal was to save construction costs by “maximizing segregated on-street running.” At-grade trains are certainly cheaper to build than subways.

    • snogglethorpe says:

      What’s important is that there be many points of potential transfer, good coverage, and not too much zig-zagging-about (some is fine of course). The difference in efficiency between a rigid grid and a “sufficiently grid-like network” is probably minor.

      Even if a grid pattern is used “in general” (e.g. for buses), it’s of course not necessary that all routes follow that grid, and it may be more important for (the relatively few) heavy trunk routes (like subways) to break the grid in favor of connecting major nodes and following development patterns (neither of which necessarily respect the grid) more directly. They’ll still intersect the general grid to roughly the same degree as if they followed the grid themselves.

    • Eric says:

      4) A grid is much more comprehensible and easier to navigate.

  3. letsgola says:

    I think the shape of the network will depend on the land use patterns some as well. In Boston, for example, the buses are sort of a crude net based on the arterials between squares, sort of hub-and-spoke. The “beltway” lines like the 1, 47, and 66 have tortuous routes because the street grid wasn’t really set up for trips in those directions, but those routes still seem to have pretty high ridership.

    The Los Angeles HRT/LRT network is sort of hub-and-spoke now, with the Green Line as an oddball, but it’s going to change with Crenshaw and future proposals like a Valley-Westwood-LAX-Long Beach route that more or less parallels the 405. There are other candidates, like an Orange Line extension to Burbank and Pasadena. Of course, the LA region is pretty unusual in terms of land use patterns, and downtown LA is small as a job center in the regional scheme of things (it’s only something like 3% of employment), so most cities probalby would end up with a downtown mesh & hub-spoke like you say.

    • Alon Levy says:

      Yeah, LA should end up with a mesh, with the outer ends framed by the Green Line, a Sepulveda/405 line, an LRT-ified Orange Line extenstion to Pasadena, and maybe a north-south line to the east of Downtown. But note that the spokes are being built first.

      But note also how even the LA lines do have various zigzags – the Red Line doesn’t look like any competently-designed bus route. Zigzags add to route length, but don’t reduce average speed much, unlike the case for buses.

    • Matthew says:

      Pretty much all the bus routes in Boston are based on old trolley lines, and in many cases the arterials were built up around those trolleys. So in a way, it’s partially like they were subway transit in that the development followed the lines, instead of the lines being dictated purely by existing street network.

      Also I might add that these crosstown lines that you mention are all “franken-routes” in that they were patched together from pieces of older routes. The 1 was created from two separate streetcar routes which connected at what is now Hynes Convention Center. The 66 was formerly two bustituted lines which connected at Union Square (Allston). The previous 66 only went between Allston and Dudley Square. Then you had to connect to the old 86 to get to Harvard Square (and it went onto Union Square (Somerville) on a segment which is part of the oldest horsecar route in the region). So one of the reasons they’re so screwy is that they’re pieces of old routes patched together, and there’s sharp political resistance against rationalizing them.

      • Adirondacker12800 says:

        The same happened all over the Northeast and Midwest. And in places like Los Angeles, The trolley ( or even the horsecar ) was extended to the farmland outside of town and there was loud sucking sound as people moved out to the new suburbs. The bus lines in Newark have the same numbers as the trolley routes they bustituted. And some of them replaced the horsecar. They still turn around where the trolley loop had been…. The trolley company goes out as far as the road that’s been there since the colonists wore down a down road to bring things to market and development got that far until the trolley line extended farther out. So the first wave is a bit denser and even today the place where density – and riders – drops offs is where the trolley used to turn around when it first starting running.

      • Alon Levy says:

        Are the 1 and 66 actually screwy? They seem like solid crosstown routes on a map – the 1 follows a major arterial street, and the 66 connects Harvard with the busiest stop on each of the B, C, and D branches of the Green Line.

        Old streetcar routes weren’t anything like modern bus routes as far as optimal routing was concerned. They were a lot more CBD-centric, although I think Boston’s square-based system is an exception to that. (But in Vancouver, the CBD-centricity of the network lives in the current trolleywire network, which excludes the most important crosstown routes, the 25, 41, and 49.) They turned a lot, because when there are no cars, zigzags don’t or barely reduce your speed, but merely increase travel distance.

        • letsgola says:

          The 1 is a rational route, and so is the 66 except maybe Union Sq jog. Problem is that crosstown “arterials” in Boston often only have one lane, which doesn’t work wonders for reliability…

        • Matthew says:

          The 1 is fairly rational except for a jog at one end. The 47 takes a significant detour as well, to serve Longwood. The 66 makes an arc which hits up just about every busy spot possible. Good for ridership I guess, bad for reliability. It also makes it worse by winding around some weird detours for historical reasons, particularly in Allston. I think it could use some short turn variants.

          Number of lanes isn’t really helpful, as the wider arterials just get clogged with more cars. Mass ave in particular.

  4. Pingback: Streetcars vs. Light Rail vs. Buses - Urban, city, town planning, land use, zoning, transportation and transit, environmental issues, urban design, community development, subdivisions, revitalization - Page 2 - City-Data Forum

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