Urban Freeways and Rapid Transit

A ride-hailing trip today reminded me of something about freeway travel in cities – namely, it is untethered from the surface street network. Oddly enough, for a different reason this is equally true of rapid transit. The commonality to these two ways of travel is that they change the geography of the city, rather than just extending the range of walking along the usual paths as surface arterial streets and surface transit do.

Rapid transit compression

Rapid transit networks compress distances along the lines, and by the same token magnify distances in orthogonal directions. Manhattan is a good example of how this works: north of Midtown the subway only runs north-south, not east-west, so there are separate East Side and West Side cultures. Moreover, as middle-class gentrifiers are displaced by rising rents coming from even richer gentrifiers, they tend to move along subway lines, and thus people from the Upper West Side and Columbia end up in Washington Heights and Inwood.

The contrast here is with surface transit. Bus networks are far too dense to have the same effect. A citywide bus grid would offer 15 km/h transit in all directions in New York, and a tramway grid like what parts of Berlin have (and what big Eastern European cities like Prague and Budapest have) offers 15-20 km/h transit in all directions. It extends walking, in the sense that the most important throughfares probably get their own routes, or if they don’t they are closely parallel with roads with surface transit.

This is not how rapid transit works. A handful of very strong orthogonal routes can and should get rapid transit, hence the Ringbahn, M2/M6 in Paris, and the under-construction M15 – and by the same token, 125th Street in New York should get a subway extension off of Second Avenue. But that still leaves the city with a wealth of major routes that have no reason to get rapid transit, ever. Most of these are crosstown routes, for example the east-west streets of Manhattan, but in less gridded cities they can just be major streets that don’t quite fit into a regionwide radial metro network.

Rapid transit spikiness

I get a lot of pushback when I talk about this, but rapid transit encourages spiky density. This does not mean that every transit city is spiky and every spiky city is a transit city. Density in Paris within the city is fairly uniform, aided by zoning rules that prohibit high-rises even though many could succeed commercially on top of Métro transfer points or RER stations. In the other direction, some American auto-oriented cities have spiky density near transit, like San Diego’s Mission Valley or Atlanta’s Buckhead, but it’s not big enough a development to permit people to comfortably walk and take transit to all destinations.

Nonetheless, for the most part, rapid transit tends to be associated with spiky development forms, especially if it’s been built more recently and if the interstation is long (as in Vancouver, Singapore, Hong Kong, or Stockholm). This isn’t really how a pedestrian city works: pedestrians have no need for spikiness because they don’t have particular distinguished stations – at most, the corner nodes are distinguished, but that includes all corners, which are placed at far shorter intervals than subway stops.

Freeways as street bypasses

Surface transit promotes urban forms that look like an extended pedestrian city. This is equally true of surface roads designed around car access. The car was originally not supposed to take over the entire city, but merely provide convenient intra-urban transportation at a faster speed than walking. It was originally just a faster, more private, more segregated streetcar. The effect on urbanism was to reduce overall density (as did the streetcars and rapid transit in New York, which used to have inhuman overcrowding levels on the Lower East Side), but not to change the urban form beyond that.

Freeways, like rapid transit, are completely different. This does not mean that they change the city in the same way as rapid transit, just that both operate independently of the usual street grid. Freeways, like rapid transit, compress travel distances along the freeway, and simultaneously lengthen them in all other directions because of the effect of traffic congestion.

Moreover, freeways are different from rapid transit in typical alignments. They are far more land-intensive, which is why they tend to be placed in formerly marginal parts of the city. This can include the waterfront if it is originally industrial and low-value, as it was in midcentury America, rather than a place of high-end residential consumption because of the views.

Interface with the street

How does a surface street transit network interface with either rapid transit or freeways?

With rapid transit, the answer is that surface transit is slow, so it should feed rapid transit using transfers, which may be timed if the trains are not so frequent (say, 15 minutes or worse, as is common on suburban rail branches). Rapid transit should then be constructed to connect with surface transit this way, that is the stations should be at intersections with arterial corridors for bus connections.

With freeways, the answer is that often interface is impossible. San Diego provides a convenient example: there is an arterial road that’s great for buses running northward from city center toward the beachfront neighborhood of Pacific Beach. But there’s also a parallel freeway inland, so drivers mostly use the freeway, and commerce on the north-south arterial is neglected. In contrast, the main east-west arterials feeding the freeway are bustling, and one of them has of the city’s strongest buses. Buses can make stops on these arterials and then express to city center on the freeway, but on the freeway itself the buses are not very efficient since there’s minimal turnover, and chaining a few neighborhoods together on one frequent route is usually not possible.

27 comments

  1. Ottawa

    How should freeways and rapid transit interface, for example, in cities of North America with a strong free way network that are just beginning to develop rapid transit?

    • Alon Levy

      They usually can’t… rapid transit should aim to serve the corridors it can serve, which are almost never in freeway medians. Rather, arterial streets and near-arterial ROWs (e.g. a closely parallel rail or power line ROW) are the name of the game; sometimes rail ROWs are good too, but in North America the nearby land use tends to be industrial rather than residential or commercial.

    • RossB

      For cities like that (which are common in the U. S.) the main interface should be at the edge of the transit system, at the edge of the density. Building a good “transit center” there, with connecting bus service could be very cost effective. Typically you won’t get many walk-up riders (because it is close to a freeway) but you maximize suburban bus integration. The buses can run as expresses — hopefully in bus or HOV lanes — and quickly connect to the more urban trips-from-everywhere-to-everywhere mass transit system.

      What you should avoid is continuing to follow the freeway, mimicking it. I think that is what Alon is getting it. Building a mass transit system in the freeway median is almost always a mistake.

    • Henry Miller

      The freeway can become your bus only lanes. That is about it, and obviously it won’t happen (political reasons) until your transit system has evolved a lot farther than any city in the US has even come close to.

      Transit needs to find new routes that are somewhat far from the freeway – to attract people who have a long detour to the freeway and more likely to find the negatives of transit (frequency and travel time tend to be lower, especially off peak) wroth the trade offs. Make them your early mass. Of course you need to cross those busy freeway feeder streets, you grab people off the bus who would have previously road the bus to the rapid system running on the freeway.

      You can also put transit on the freeway feeder roads. If people are transferring to the bus at the freeway try to get the to transfer a little farther away.

      • RossB

        The freeway can become your bus only lanes. That is about it, and obviously it won’t happen (political reasons) until your transit system has evolved a lot farther than any city in the US has even come close to.

        So far as I know, there are no bus-only freeways in the U. S. But there are HOV and bus lanes in various cities. Since there are no traffic lights or stops on the freeway, one lane is sufficient. The big issue for many is whether the lane is HOV-2 or HOV-3 (or more). At least in Seattle, HOV-2 lanes are often crowded. There are just too many 2 person carpools. HOV-3, in contrast, is often smooth sailing. One example of this is on State Route 520: https://goo.gl/maps/TJMQxNPPPhULJhuH7. There are freeway based bus stops (that have bus only lanes https://goo.gl/maps/vmL8uKS4rn8m7bgv5) and HOV-3 lanes. The light rail system goes under the ship canal, with the freeway a little bit above it. The city didn’t build a station there, despite the fact that about 25,000 or so riders a day take buses involving that freeway. If they had, then the bus could have connected there easily. Instead, connecting buses leave the freeway, and follow surface streets to the nearest station. It isn’t that far away, and they are in the process of building HOV-3 only ramps, along with bus-only lanes on the road (some of which exists now — https://goo.gl/maps/jVkP5hvGZ9Cms6jb8). But it still involves a movable bridge crossing, which can delay the buses.

        A more seamless interface will exist to the north. This will be the northern terminus of the light rail line in a few years: https://goo.gl/maps/ahcSCEZky5XHFPDo6. You can see that there are carpool lanes leading right to an existing transit center that will eventually lead to a light rail station. The biggest problem is that the carpool lanes are two person only. The biggest spending flaw is that the line simply went too far. Something similar — built farther south — would have been a much better value, and provided just about as much functionality. But instead they decided to extend the rail next to the freeway, instead of ending it where the population density and employment density take a sudden drop (at the city limits).

        • adirondacker12800

          Put the park-n-ride and the feeder buses beyond the density they aren’t clogging traffic where there is density. .

          • adirondacker12800

            The people who want to drive to the railroad don’t clog up “downtown”, they are out by the highway.

  2. Herbert

    Too small and disjointed a rapid transit network and you lose in forced transfers what you gain in in-vehicle speed.

    Too large a distance between stops and you lose in access time what you gain in in-vehicle speed.

    Cities of a certain size fare better with a Stadtbahn than a full subway…

    • Alon Levy

      Why not both?

      (I.e. Prague, Vienna, Budapest… but then Stockholm doesn’t even have the streetcar layer and is alright.)

        • Alon Levy

          It’s not really a network. Two lines are outer lines connecting a metro station to low-density areas, one is a slow circumferential, one is another outer line but connects to city center rather than an outlying T-bana station.

          • Herbert

            Why is Nuremberg an example of a terribly designed disjointed “network”? For one, any ride that starts on a tram in the west and ends on a tram in the east is a three seat ride…

      • lcpitkan

        I guess both, if you can afford it and have sufficient ridership potential. In theory you probably want 2-3 levels of urban public transport lines for different trip lengths, eg. https://www.slideshare.net/andrewbnash/2015-nashptlevels7jan154pptx . But this does cost a lot of money.
        Stockholm could do with higher capacity on the surface. Some of the trunk bus lines are severely crowded as is the metro in the city centre. But making it work would require radical changes to street layouts and a quite a bit of money. Extending the metro and regional rail to serve population growth continues to be a higher priority.

  3. adirondacker12800

    rapid transit tends to be associated with spiky development forms,

    If there aren’t any destinations ( spikes ) you don’t need the mass transit. And there were spikes before there was mass transit. Which is why people went out and invented mass transit.

    • Alon Levy

      No, there were no spikes back then. There was uniform high residential density and mixed-and-commercializing density in city center.

      • adirondacker12800

        Why did they need canals and railroads?
        ….Silly them moving the seat of government from the city of London all the way out to Westminster.

        • fjod

          Yes, London strikes me as the only European city I’m aware of that was definitely spiky before mass transit (and before rail in general), with the obvious spikes being the City, the West End and Westminster. Rome, Naples and Edinburgh might also be candidates but I’m less sure. Of course I suppose cities back then were too small to have more than three or four spikes.

    • RossB

      Spiky development has more to do with zoning than anything else. Often the municipality allows high-rise growth close to transit, encouraging it. But it is only one factor that can lead to such demand. Seattle, for example, has grown quite a bit over the last few years (as much as any city in the U. S.) and much of it was centered around particular neighborhoods. Inside Seattle there really isn’t a strong relationship between the growth and mass transit, though. It is more about where they allow growth (which is only in a handful of places) and where they don’t (about 2/3 of the city). The result is a fairly spiky city (although not as spiky as suburban Vancouver or Toronto).

      Speaking of which, these all or nothing policies often lead to a city with high housing costs. A city like Montreal, with more widespread density, is more affordable. This writer calls these policies “the grand bargain”: https://pricetags.ca/2019/10/17/the-grand-bargain-illustrated/?fbclid=IwAR1yAeWGDUzZjG8vLaBPhwJPYh9fxm0tIuVXUbfLVYFqbT1f7zJy5H7s7D0

  4. lcpitkan

    While surface lines should feed rapid transit, I would contend that this isn’t their only role ie. they serve local trips as well. Probably not really implied above either. But this does have an impact on network design: some feeder networks for heavy rail are geared almost completely towards the feeder role, others also serve local or circumferential/orbital trips at the same time.

  5. lcpitkan

    And a tangential though from something a friend has said: in many US cities the (arterial) street network is very high capacity. Thus urban freeways can be true bottlenecks. In most European cities the street network is much lower capacity and most urban motorway congestion arises from the exits to the street network. This might also explain why ramp metering is common in the US (limiting freeway congestion), but not in Europe. What we use instead is metering access from motorways to the street network to keep the latter functioning.

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